HTML 5

Draft Recommendation — 30 April 2009

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Multiple-page version:
http://whatwg.org/html5
One-page version:
http://www.whatwg.org/specs/web-apps/current-work/
PDF print versions:
A4: http://www.whatwg.org/specs/web-apps/current-work/html5-a4.pdf
Letter: http://www.whatwg.org/specs/web-apps/current-work/html5-letter.pdf
Version history:
Twitter messages (non-editorial changes only): http://twitter.com/WHATWG
Commit-Watchers mailing list: http://lists.whatwg.org/listinfo.cgi/commit-watchers-whatwg.org
Interactive Web interface: http://html5.org/tools/web-apps-tracker
Subversion interface: http://svn.whatwg.org/
HTML diff with the last version in Subversion: http://whatwg.org/specs/web-apps/current-work/index-diff
Issues:
To send feedback: whatwg@whatwg.org
To view and vote on feedback: http://www.whatwg.org/issues/
Editor:
Ian Hickson, Google, ian@hixie.ch

Abstract

This specification evolves HTML and its related APIs to ease the authoring of Web-based applications. Additions include context menus, a direct-mode graphics canvas, a full duplex client-server communication channel, more semantics, audio and video, various features for offline Web applications, sandboxed iframes, and scoped styling. Heavy emphasis is placed on keeping the language backwards compatible with existing legacy user agents and on keeping user agents backwards compatible with existing legacy documents.

Status of this document

This is a work in progress! This document is changing on a daily if not hourly basis in response to comments and as a general part of its development process. Comments are very welcome, please send them to whatwg@whatwg.org. Thank you.

The current focus is in responding to the outstanding feedback. (There is a chart showing current progress.)

Implementors should be aware that this specification is not stable. Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the call for implementations should join the WHATWG mailing list and take part in the discussions.

This specification is also being produced by the W3C HTML WG. The two specifications are identical from the table of contents onwards.

This specification is intended to replace (be the new version of) what was previously the HTML4, XHTML 1.x, and DOM2 HTML specifications.

Stability

Different parts of this specification are at different levels of maturity.

Some of the more major known issues are marked like this. There are many other issues that have been raised as well; the issues given in this document are not the only known issues! Also, firing of events needs to be unified (right now some bubble, some don't, they all use different text to fire events, etc).

Table of contents

  1. 1 Introduction
    1. 1.1 Background
    2. 1.2 Audience
    3. 1.3 Scope
    4. 1.4 History
    5. 1.5 Design notes
      1. 1.5.1 Serializability of script execution
      2. 1.5.2 Compliance with other specifications
    6. 1.6 Relationships to other specifications
      1. 1.6.1 Relationship to HTML 4.01 and DOM2 HTML
      2. 1.6.2 Relationship to XHTML 1.x
      3. 1.6.3 Relationship to XHTML2 and XForms
    7. 1.7 HTML vs XHTML
    8. 1.8 Structure of this specification
      1. 1.8.1 How to read this specification
      2. 1.8.2 Typographic conventions
  2. 2 Common infrastructure
    1. 2.1 Terminology
      1. 2.1.1 XML
      2. 2.1.2 DOM trees
      3. 2.1.3 Scripting
      4. 2.1.4 Plugins
      5. 2.1.5 Character encodings
    2. 2.2 Conformance requirements
      1. 2.2.1 Dependencies
      2. 2.2.2 Features defined in other specifications
      3. 2.2.3 Common conformance requirements for APIs exposed to JavaScript
    3. 2.3 Case-sensitivity and string comparison
    4. 2.4 Common microsyntaxes
      1. 2.4.1 Common parser idioms
      2. 2.4.2 Boolean attributes
      3. 2.4.3 Keywords and enumerated attributes
      4. 2.4.4 Numbers
        1. 2.4.4.1 Non-negative integers
        2. 2.4.4.2 Signed integers
        3. 2.4.4.3 Real numbers
        4. 2.4.4.4 Ratios
        5. 2.4.4.5 Percentages and lengths
        6. 2.4.4.6 Lists of integers
        7. 2.4.4.7 Lists of dimensions
      5. 2.4.5 Dates and times
        1. 2.4.5.1 Months
        2. 2.4.5.2 Dates
        3. 2.4.5.3 Times
        4. 2.4.5.4 Local dates and times
        5. 2.4.5.5 Global dates and times
        6. 2.4.5.6 Weeks
        7. 2.4.5.7 Vaguer moments in time
      6. 2.4.6 Colors
      7. 2.4.7 Space-separated tokens
      8. 2.4.8 Comma-separated tokens
      9. 2.4.9 References
    5. 2.5 URLs
      1. 2.5.1 Terminology
      2. 2.5.2 Parsing URLs
      3. 2.5.3 Resolving URLs
      4. 2.5.4 Dynamic changes to base URLs
      5. 2.5.5 Interfaces for URL manipulation
    6. 2.6 Fetching resources
      1. 2.6.1 Protocol concepts
      2. 2.6.2 Encrypted HTTP and related security concerns
    7. 2.7 Determining the type of a resource
      1. 2.7.1 Content-Type metadata
      2. 2.7.2 Content-Type sniffing: Web pages
      3. 2.7.3 Content-Type sniffing: text or binary
      4. 2.7.4 Content-Type sniffing: unknown type
      5. 2.7.5 Content-Type sniffing: image
      6. 2.7.6 Content-Type sniffing: feed or HTML
    8. 2.8 Character encodings
    9. 2.9 Common DOM interfaces
      1. 2.9.1 Reflecting content attributes in DOM attributes
      2. 2.9.2 Collections
        1. 2.9.2.1 HTMLCollection
        2. 2.9.2.2 HTMLFormControlsCollection
        3. 2.9.2.3 HTMLOptionsCollection
      3. 2.9.3 DOMTokenList
      4. 2.9.4 Safe passing of structured data
      5. 2.9.5 DOMStringMap
      6. 2.9.6 DOM feature strings
      7. 2.9.7 Exceptions
      8. 2.9.8 Garbage collection
  3. 3 Semantics and structure of HTML documents
    1. 3.1 Introduction
    2. 3.2 Documents
      1. 3.2.1 Documents in the DOM
      2. 3.2.2 Security
      3. 3.2.3 Resource metadata management
      4. 3.2.4 DOM tree accessors
    3. 3.3 Elements
      1. 3.3.1 Semantics
      2. 3.3.2 Elements in the DOM
      3. 3.3.3 Global attributes
        1. 3.3.3.1 The id attribute
        2. 3.3.3.2 The title attribute
        3. 3.3.3.3 The lang and xml:lang attributes
        4. 3.3.3.4 The xml:base attribute (XML only)
        5. 3.3.3.5 The dir attribute
        6. 3.3.3.6 The class attribute
        7. 3.3.3.7 The style attribute
        8. 3.3.3.8 Embedding custom non-visible data
    4. 3.4 Content models
      1. 3.4.1 Kinds of content
        1. 3.4.1.1 Metadata content
        2. 3.4.1.2 Flow content
        3. 3.4.1.3 Sectioning content
        4. 3.4.1.4 Heading content
        5. 3.4.1.5 Phrasing content
        6. 3.4.1.6 Embedded content
        7. 3.4.1.7 Interactive content
      2. 3.4.2 Transparent content models
    5. 3.5 Paragraphs
    6. 3.6 APIs in HTML documents
    7. 3.7 Dynamic markup insertion
      1. 3.7.1 Controlling the input stream
      2. 3.7.2 document.write()
      3. 3.7.3 document.writeln()
      4. 3.7.4 innerHTML
      5. 3.7.5 outerHTML
      6. 3.7.6 insertAdjacentHTML()
  4. 4 The elements of HTML
    1. 4.1 The root element
      1. 4.1.1 The html element
    2. 4.2 Document metadata
      1. 4.2.1 The head element
      2. 4.2.2 The title element
      3. 4.2.3 The base element
      4. 4.2.4 The link element
      5. 4.2.5 The meta element
        1. 4.2.5.1 Standard metadata names
        2. 4.2.5.2 Other metadata names
        3. 4.2.5.3 Pragma directives
        4. 4.2.5.4 Other pragma directives
        5. 4.2.5.5 Specifying the document's character encoding
      6. 4.2.6 The style element
      7. 4.2.7 Styling
    3. 4.3 Scripting
      1. 4.3.1 The script element
        1. 4.3.1.1 Scripting languages
        2. 4.3.1.2 Inline documentation for external scripts
      2. 4.3.2 The noscript element
    4. 4.4 Sections
      1. 4.4.1 The body element
      2. 4.4.2 The section element
      3. 4.4.3 The nav element
      4. 4.4.4 The article element
      5. 4.4.5 The aside element
      6. 4.4.6 The h1, h2, h3, h4, h5, and h6 elements
      7. 4.4.7 The hgroup element
      8. 4.4.8 The header element
      9. 4.4.9 The footer element
      10. 4.4.10 The address element
      11. 4.4.11 Headings and sections
        1. 4.4.11.1 Creating an outline
        2. 4.4.11.2 Distinguishing site-wide headings from page headings
    5. 4.5 Grouping content
      1. 4.5.1 The p element
      2. 4.5.2 The hr element
      3. 4.5.3 The br element
      4. 4.5.4 The pre element
      5. 4.5.5 The dialog element
      6. 4.5.6 The blockquote element
      7. 4.5.7 The ol element
      8. 4.5.8 The ul element
      9. 4.5.9 The li element
      10. 4.5.10 The dl element
      11. 4.5.11 The dt element
      12. 4.5.12 The dd element
      13. 4.5.13 Common grouping idioms
        1. 4.5.13.1 Tag clouds
    6. 4.6 Text-level semantics
      1. 4.6.1 The a element
      2. 4.6.2 The q element
      3. 4.6.3 The cite element
      4. 4.6.4 The em element
      5. 4.6.5 The strong element
      6. 4.6.6 The small element
      7. 4.6.7 The mark element
      8. 4.6.8 The dfn element
      9. 4.6.9 The abbr element
      10. 4.6.10 The time element
      11. 4.6.11 The progress element
      12. 4.6.12 The meter element
      13. 4.6.13 The code element
      14. 4.6.14 The var element
      15. 4.6.15 The samp element
      16. 4.6.16 The kbd element
      17. 4.6.17 The sub and sup elements
      18. 4.6.18 The span element
      19. 4.6.19 The i element
      20. 4.6.20 The b element
      21. 4.6.21 The bdo element
      22. 4.6.22 The ruby element
      23. 4.6.23 The rt element
      24. 4.6.24 The rp element
      25. 4.6.25 Usage summary
      26. 4.6.26 Footnotes
    7. 4.7 Edits
      1. 4.7.1 The ins element
      2. 4.7.2 The del element
      3. 4.7.3 Attributes common to ins and del elements
      4. 4.7.4 Edits and paragraphs
      5. 4.7.5 Edits and lists
    8. 4.8 Embedded content
      1. 4.8.1 The figure element
      2. 4.8.2 The img element
        1. 4.8.2.1 Requirements for providing text to act as an alternative for images
          1. 4.8.2.1.1 A link or button containing nothing but the image
          2. 4.8.2.1.2 A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations
          3. 4.8.2.1.3 A short phrase or label with an alternative graphical representation: icons, logos
          4. 4.8.2.1.4 Text that has been rendered to a graphic for typographical effect
          5. 4.8.2.1.5 A graphical representation of some of the surrounding text
          6. 4.8.2.1.6 A purely decorative image that doesn't add any information
          7. 4.8.2.1.7 A group of images that form a single larger picture with no links
          8. 4.8.2.1.8 A group of images that form a single larger picture with links
          9. 4.8.2.1.9 A key part of the content
          10. 4.8.2.1.10 An image not intended for the user
          11. 4.8.2.1.11 An image in an e-mail or private document intended for a specific person who is known to be able to view images
          12. 4.8.2.1.12 General guidelines
          13. 4.8.2.1.13 Guidance for markup generators
          14. 4.8.2.1.14 Guidance for conformance checkers
      3. 4.8.3 The iframe element
      4. 4.8.4 The embed element
      5. 4.8.5 The object element
      6. 4.8.6 The param element
      7. 4.8.7 The video element
        1. 4.8.7.1 Video and audio codecs for video elements
      8. 4.8.8 The audio element
        1. 4.8.8.1 Audio codecs for audio elements
      9. 4.8.9 The source element
      10. 4.8.10 Media elements
        1. 4.8.10.1 Error codes
        2. 4.8.10.2 Location of the media resource
        3. 4.8.10.3 Media types
        4. 4.8.10.4 Network states
        5. 4.8.10.5 Loading the media resource
        6. 4.8.10.6 Offsets into the media resource
        7. 4.8.10.7 The ready states
        8. 4.8.10.8 Cue ranges
        9. 4.8.10.9 Playing the media resource
        10. 4.8.10.10 Seeking
        11. 4.8.10.11 User interface
        12. 4.8.10.12 Time ranges
        13. 4.8.10.13 Event summary
        14. 4.8.10.14 Security and privacy considerations
      11. 4.8.11 The canvas element
        1. 4.8.11.1 The 2D context
          1. 4.8.11.1.1 The canvas state
          2. 4.8.11.1.2 Transformations
          3. 4.8.11.1.3 Compositing
          4. 4.8.11.1.4 Colors and styles
          5. 4.8.11.1.5 Line styles
          6. 4.8.11.1.6 Shadows
          7. 4.8.11.1.7 Simple shapes (rectangles)
          8. 4.8.11.1.8 Complex shapes (paths)
          9. 4.8.11.1.9 Text
          10. 4.8.11.1.10 Images
          11. 4.8.11.1.11 Pixel manipulation
          12. 4.8.11.1.12 Drawing model
        2. 4.8.11.2 Color spaces and color correction
        3. 4.8.11.3 Security with canvas elements
      12. 4.8.12 The map element
      13. 4.8.13 The area element
      14. 4.8.14 Image maps
        1. 4.8.14.1 Authoring
        2. 4.8.14.2 Processing model
      15. 4.8.15 MathML
      16. 4.8.16 SVG
      17. 4.8.17 Dimension attributes
    9. 4.9 Tabular data
      1. 4.9.1 Introduction
      2. 4.9.2 The table element
      3. 4.9.3 The caption element
      4. 4.9.4 The colgroup element
      5. 4.9.5 The col element
      6. 4.9.6 The tbody element
      7. 4.9.7 The thead element
      8. 4.9.8 The tfoot element
      9. 4.9.9 The tr element
      10. 4.9.10 The td element
      11. 4.9.11 The th element
      12. 4.9.12 Attributes common to td and th elements
      13. 4.9.13 Processing model
        1. 4.9.13.1 Forming a table
        2. 4.9.13.2 Forming relationships between data cells and header cells
    10. 4.10 Forms
      1. 4.10.1 The form element
      2. 4.10.2 The fieldset element
      3. 4.10.3 The label element
      4. 4.10.4 The input element
        1. 4.10.4.1 States of the type attribute
          1. 4.10.4.1.1 Hidden state
          2. 4.10.4.1.2 Text state and Search state
          3. 4.10.4.1.3 URL state
          4. 4.10.4.1.4 E-mail state
          5. 4.10.4.1.5 Password state
          6. 4.10.4.1.6 Date and Time state
          7. 4.10.4.1.7 Date state
          8. 4.10.4.1.8 Month state
          9. 4.10.4.1.9 Week state
          10. 4.10.4.1.10 Time state
          11. 4.10.4.1.11 Local Date and Time state
          12. 4.10.4.1.12 Number state
          13. 4.10.4.1.13 Range state
          14. 4.10.4.1.14 Color state
          15. 4.10.4.1.15 Checkbox state
          16. 4.10.4.1.16 Radio Button state
          17. 4.10.4.1.17 File Upload state
          18. 4.10.4.1.18 Submit Button state
          19. 4.10.4.1.19 Image Button state
          20. 4.10.4.1.20 Reset Button state
          21. 4.10.4.1.21 Button state
        2. 4.10.4.2 Common input element attributes
          1. 4.10.4.2.1 The autocomplete attribute
          2. 4.10.4.2.2 The list attribute
          3. 4.10.4.2.3 The readonly attribute
          4. 4.10.4.2.4 The size attribute
          5. 4.10.4.2.5 The required attribute
          6. 4.10.4.2.6 The multiple attribute
          7. 4.10.4.2.7 The maxlength attribute
          8. 4.10.4.2.8 The pattern attribute
          9. 4.10.4.2.9 The min and max attributes
          10. 4.10.4.2.10 The step attribute
          11. 4.10.4.2.11 The placeholder attribute
        3. 4.10.4.3 Common input element APIs
        4. 4.10.4.4 Common event behaviors
      5. 4.10.5 The button element
      6. 4.10.6 The select element
      7. 4.10.7 The datalist element
      8. 4.10.8 The optgroup element
      9. 4.10.9 The option element
      10. 4.10.10 The textarea element
      11. 4.10.11 The keygen element
      12. 4.10.12 The output element
      13. 4.10.13 Association of controls and forms
      14. 4.10.14 Attributes common to form controls
        1. 4.10.14.1 Naming form controls
        2. 4.10.14.2 Enabling and disabling form controls
        3. 4.10.14.3 A form control's value
        4. 4.10.14.4 Autofocusing a form control
        5. 4.10.14.5 Limiting user input length
        6. 4.10.14.6 Form submission
      15. 4.10.15 Constraints
        1. 4.10.15.1 Definitions
        2. 4.10.15.2 Constraint validation
        3. 4.10.15.3 The constraint validation API
        4. 4.10.15.4 Security
      16. 4.10.16 Form submission
        1. 4.10.16.1 Introduction
        2. 4.10.16.2 Implicit submission
        3. 4.10.16.3 Form submission algorithm
        4. 4.10.16.4 URL-encoded form data
        5. 4.10.16.5 Multipart form data
        6. 4.10.16.6 Plain text form data
      17. 4.10.17 Resetting a form
      18. 4.10.18 Event dispatch
    11. 4.11 Interactive elements
      1. 4.11.1 The details element
      2. 4.11.2 The datagrid element
        1. 4.11.2.1 Introduction
          1. 4.11.2.1.1 Example: a datagrid backed by a static table element
          2. 4.11.2.1.2 Example: a datagrid backed by nested ol elements
          3. 4.11.2.1.3 Example: a datagrid backed by a server
        2. 4.11.2.2 Populating the datagrid
          1. 4.11.2.2.1 The listener
          2. 4.11.2.2.2 The columns
          3. 4.11.2.2.3 The rows
          4. 4.11.2.2.4 The cells
        3. 4.11.2.3 Listening to notifications from the datagrid
      3. 4.11.3 The command element
      4. 4.11.4 The bb element
        1. 4.11.4.1 Browser button types
          1. 4.11.4.1.1 The make application state
      5. 4.11.5 The menu element
        1. 4.11.5.1 Introduction
        2. 4.11.5.2 Building menus and tool bars
        3. 4.11.5.3 Context menus
        4. 4.11.5.4 Tool bars
      6. 4.11.6 Commands
        1. 4.11.6.1 Using the a element to define a command
        2. 4.11.6.2 Using the button element to define a command
        3. 4.11.6.3 Using the input element to define a command
        4. 4.11.6.4 Using the option element to define a command
        5. 4.11.6.5 Using the command element to define a command
        6. 4.11.6.6 Using the bb element to define a command
    12. 4.12 Miscellaneous elements
      1. 4.12.1 The legend element
      2. 4.12.2 The div element
    13. 4.13 Matching HTML elements using selectors
  5. 5 Web browsers
    1. 5.1 Browsing contexts
      1. 5.1.1 Nested browsing contexts
        1. 5.1.1.1 Navigating nested browsing contexts in the DOM
      2. 5.1.2 Auxiliary browsing contexts
        1. 5.1.2.1 Navigating auxiliary browsing contexts in the DOM
      3. 5.1.3 Secondary browsing contexts
      4. 5.1.4 Security
      5. 5.1.5 Groupings of browsing contexts
      6. 5.1.6 Browsing context names
    2. 5.2 The WindowProxy object
    3. 5.3 The Window object
      1. 5.3.1 Security
      2. 5.3.2 APIs for creating and navigating browsing contexts by name
      3. 5.3.3 Accessing other browsing contexts
      4. 5.3.4 Named access on the Window object
      5. 5.3.5 Garbage collection and browsing contexts
      6. 5.3.6 Browser interface elements
    4. 5.4 Origin
      1. 5.4.1 Relaxing the same-origin restriction
    5. 5.5 Scripting
      1. 5.5.1 Introduction
      2. 5.5.2 Enabling and disabling scripting
      3. 5.5.3 Processing model
        1. 5.5.3.1 Definitions
        2. 5.5.3.2 Calling scripts
        3. 5.5.3.3 Creating scripts
        4. 5.5.3.4 Killing scripts
      4. 5.5.4 Event loops
        1. 5.5.4.1 Definitions
        2. 5.5.4.2 Processing model
        3. 5.5.4.3 Generic task sources
      5. 5.5.5 The javascript: protocol
      6. 5.5.6 Events
        1. 5.5.6.1 Event handler attributes
        2. 5.5.6.2 Event handler attributes on elements, Document objects, and Window objects
        3. 5.5.6.3 Event firing
        4. 5.5.6.4 Events and the Window object
        5. 5.5.6.5 Runtime script errors
    6. 5.6 User prompts
      1. 5.6.1 Simple dialogs
      2. 5.6.2 Printing
      3. 5.6.3 Dialogs implemented using separate documents
    7. 5.7 System state and capabilities
      1. 5.7.1 Client identification
      2. 5.7.2 Custom protocol and content handlers
        1. 5.7.2.1 Security and privacy
        2. 5.7.2.2 Sample user interface
      3. 5.7.3 Manually releasing the storage mutex
    8. 5.8 Offline Web applications
      1. 5.8.1 Introduction
      2. 5.8.2 Application caches
      3. 5.8.3 The cache manifest syntax
        1. 5.8.3.1 A sample manifest
        2. 5.8.3.2 Writing cache manifests
        3. 5.8.3.3 Parsing cache manifests
      4. 5.8.4 Updating an application cache
      5. 5.8.5 Matching a fallback namespace
      6. 5.8.6 The application cache selection algorithm
      7. 5.8.7 Changes to the networking model
      8. 5.8.8 Application cache API
      9. 5.8.9 Browser state
    9. 5.9 Session history and navigation
      1. 5.9.1 The session history of browsing contexts
      2. 5.9.2 The History interface
      3. 5.9.3 Activating state object entries
      4. 5.9.4 The Location interface
        1. 5.9.4.1 Security
      5. 5.9.5 Implementation notes for session history
    10. 5.10 Browsing the Web
      1. 5.10.1 Navigating across documents
      2. 5.10.2 Page load processing model for HTML files
      3. 5.10.3 Page load processing model for XML files
      4. 5.10.4 Page load processing model for text files
      5. 5.10.5 Page load processing model for images
      6. 5.10.6 Page load processing model for content that uses plugins
      7. 5.10.7 Page load processing model for inline content that doesn't have a DOM
      8. 5.10.8 Navigating to a fragment identifier
      9. 5.10.9 History traversal
      10. 5.10.10 Unloading documents
        1. 5.10.10.1 Event definition
    11. 5.11 Links
      1. 5.11.1 Hyperlink elements
      2. 5.11.2 Following hyperlinks
        1. 5.11.2.1 Hyperlink auditing
      3. 5.11.3 Link types
        1. 5.11.3.1 Link type "alternate"
        2. 5.11.3.2 Link type "archives"
        3. 5.11.3.3 Link type "author"
        4. 5.11.3.4 Link type "bookmark"
        5. 5.11.3.5 Link type "external"
        6. 5.11.3.6 Link type "feed"
        7. 5.11.3.7 Link type "help"
        8. 5.11.3.8 Link type "icon"
        9. 5.11.3.9 Link type "license"
        10. 5.11.3.10 Link type "nofollow"
        11. 5.11.3.11 Link type "noreferrer"
        12. 5.11.3.12 Link type "pingback"
        13. 5.11.3.13 Link type "prefetch"
        14. 5.11.3.14 Link type "search"
        15. 5.11.3.15 Link type "stylesheet"
        16. 5.11.3.16 Link type "sidebar"
        17. 5.11.3.17 Link type "tag"
        18. 5.11.3.18 Hierarchical link types
          1. 5.11.3.18.1 Link type "index"
          2. 5.11.3.18.2 Link type "up"
        19. 5.11.3.19 Sequential link types
          1. 5.11.3.19.1 Link type "first"
          2. 5.11.3.19.2 Link type "last"
          3. 5.11.3.19.3 Link type "next"
          4. 5.11.3.19.4 Link type "prev"
        20. 5.11.3.20 Other link types
  6. 6 User Interaction
    1. 6.1 Introduction
    2. 6.2 The hidden attribute
    3. 6.3 Activation
    4. 6.4 Scrolling elements into view
    5. 6.5 Focus
      1. 6.5.1 Sequential focus navigation
      2. 6.5.2 Focus management
      3. 6.5.3 Document-level focus APIs
      4. 6.5.4 Element-level focus APIs
    6. 6.6 The text selection APIs
      1. 6.6.1 APIs for the browsing context selection
      2. 6.6.2 APIs for the text field selections
    7. 6.7 The contenteditable attribute
      1. 6.7.1 User editing actions
      2. 6.7.2 Making entire documents editable
    8. 6.8 Spelling and grammar checking
    9. 6.9 Drag and drop
      1. 6.9.1 Introduction
      2. 6.9.2 The DragEvent and DataTransfer interfaces
      3. 6.9.3 Events fired during a drag-and-drop action
      4. 6.9.4 Drag-and-drop processing model
        1. 6.9.4.1 When the drag-and-drop operation starts or ends in another document
        2. 6.9.4.2 When the drag-and-drop operation starts or ends in another application
      5. 6.9.5 The draggable attribute
      6. 6.9.6 Copy and paste
        1. 6.9.6.1 Copy to clipboard
        2. 6.9.6.2 Cut to clipboard
        3. 6.9.6.3 Paste from clipboard
        4. 6.9.6.4 Paste from selection
      7. 6.9.7 Security risks in the drag-and-drop model
    10. 6.10 Undo history
      1. 6.10.1 Introduction
      2. 6.10.2 Definitions
      3. 6.10.3 The UndoManager interface
      4. 6.10.4 Undo: moving back in the undo transaction history
      5. 6.10.5 Redo: moving forward in the undo transaction history
      6. 6.10.6 The UndoManagerEvent interface and the undo and redo events
      7. 6.10.7 Implementation notes
    11. 6.11 Command APIs
  7. 7 Communication
    1. 7.1 Event definitions
    2. 7.2 Cross-document messaging
      1. 7.2.1 Introduction
      2. 7.2.2 Security
        1. 7.2.2.1 Authors
        2. 7.2.2.2 User agents
      3. 7.2.3 Posting messages
      4. 7.2.4 Posting messages with message ports
    3. 7.3 Channel messaging
      1. 7.3.1 Introduction
      2. 7.3.2 Message channels
      3. 7.3.3 Message ports
        1. 7.3.3.1 Ports and garbage collection
  8. 8 The HTML syntax
    1. 8.1 Writing HTML documents
      1. 8.1.1 The DOCTYPE
      2. 8.1.2 Elements
        1. 8.1.2.1 Start tags
        2. 8.1.2.2 End tags
        3. 8.1.2.3 Attributes
        4. 8.1.2.4 Optional tags
        5. 8.1.2.5 Restrictions on content models
        6. 8.1.2.6 Restrictions on the contents of CDATA and RCDATA elements
      3. 8.1.3 Text
        1. 8.1.3.1 Newlines
      4. 8.1.4 Character references
      5. 8.1.5 CDATA sections
      6. 8.1.6 Comments
    2. 8.2 Parsing HTML documents
      1. 8.2.1 Overview of the parsing model
      2. 8.2.2 The input stream
        1. 8.2.2.1 Determining the character encoding
        2. 8.2.2.2 Preprocessing the input stream
        3. 8.2.2.3 Changing the encoding while parsing
      3. 8.2.3 Parse state
        1. 8.2.3.1 The insertion mode
        2. 8.2.3.2 The stack of open elements
        3. 8.2.3.3 The list of active formatting elements
        4. 8.2.3.4 The element pointers
        5. 8.2.3.5 Other parsing state flags
      4. 8.2.4 Tokenization
        1. 8.2.4.1 Data state
        2. 8.2.4.2 Character reference data state
        3. 8.2.4.3 Tag open state
        4. 8.2.4.4 Close tag open state
        5. 8.2.4.5 Tag name state
        6. 8.2.4.6 Before attribute name state
        7. 8.2.4.7 Attribute name state
        8. 8.2.4.8 After attribute name state
        9. 8.2.4.9 Before attribute value state
        10. 8.2.4.10 Attribute value (double-quoted) state
        11. 8.2.4.11 Attribute value (single-quoted) state
        12. 8.2.4.12 Attribute value (unquoted) state
        13. 8.2.4.13 Character reference in attribute value state
        14. 8.2.4.14 After attribute value (quoted) state
        15. 8.2.4.15 Self-closing start tag state
        16. 8.2.4.16 Bogus comment state
        17. 8.2.4.17 Markup declaration open state
        18. 8.2.4.18 Comment start state
        19. 8.2.4.19 Comment start dash state
        20. 8.2.4.20 Comment state
        21. 8.2.4.21 Comment end dash state
        22. 8.2.4.22 Comment end state
        23. 8.2.4.23 DOCTYPE state
        24. 8.2.4.24 Before DOCTYPE name state
        25. 8.2.4.25 DOCTYPE name state
        26. 8.2.4.26 After DOCTYPE name state
        27. 8.2.4.27 Before DOCTYPE public identifier state
        28. 8.2.4.28 DOCTYPE public identifier (double-quoted) state
        29. 8.2.4.29 DOCTYPE public identifier (single-quoted) state
        30. 8.2.4.30 After DOCTYPE public identifier state
        31. 8.2.4.31 Before DOCTYPE system identifier state
        32. 8.2.4.32 DOCTYPE system identifier (double-quoted) state
        33. 8.2.4.33 DOCTYPE system identifier (single-quoted) state
        34. 8.2.4.34 After DOCTYPE system identifier state
        35. 8.2.4.35 Bogus DOCTYPE state
        36. 8.2.4.36 CDATA section state
        37. 8.2.4.37 Tokenizing character references
      5. 8.2.5 Tree construction
        1. 8.2.5.1 Creating and inserting elements
        2. 8.2.5.2 Closing elements that have implied end tags
        3. 8.2.5.3 Foster parenting
        4. 8.2.5.4 The "initial" insertion mode
        5. 8.2.5.5 The "before html" insertion mode
        6. 8.2.5.6 The "before head" insertion mode
        7. 8.2.5.7 The "in head" insertion mode
        8. 8.2.5.8 The "in head noscript" insertion mode
        9. 8.2.5.9 The "after head" insertion mode
        10. 8.2.5.10 The "in body" insertion mode
        11. 8.2.5.11 The "in CDATA/RCDATA" insertion mode
        12. 8.2.5.12 The "in table" insertion mode
        13. 8.2.5.13 The "in caption" insertion mode
        14. 8.2.5.14 The "in column group" insertion mode
        15. 8.2.5.15 The "in table body" insertion mode
        16. 8.2.5.16 The "in row" insertion mode
        17. 8.2.5.17 The "in cell" insertion mode
        18. 8.2.5.18 The "in select" insertion mode
        19. 8.2.5.19 The "in select in table" insertion mode
        20. 8.2.5.20 The "in foreign content" insertion mode
        21. 8.2.5.21 The "after body" insertion mode
        22. 8.2.5.22 The "in frameset" insertion mode
        23. 8.2.5.23 The "after frameset" insertion mode
        24. 8.2.5.24 The "after after body" insertion mode
        25. 8.2.5.25 The "after after frameset" insertion mode
      6. 8.2.6 The end
      7. 8.2.7 Coercing an HTML DOM into an infoset
    3. 8.3 Namespaces
    4. 8.4 Serializing HTML fragments
    5. 8.5 Parsing HTML fragments
    6. 8.6 Named character references
  9. 9 The XHTML syntax
    1. 9.1 Writing XHTML documents
    2. 9.2 Parsing XHTML documents
    3. 9.3 Serializing XHTML fragments
    4. 9.4 Parsing XHTML fragments
  10. 10 Rendering
    1. 10.1 Introduction
    2. 10.2 The CSS user agent style sheet and presentational hints
      1. 10.2.1 Introduction
      2. 10.2.2 Display types
      3. 10.2.3 Margins and padding
      4. 10.2.4 Alignment
      5. 10.2.5 Fonts and colors
      6. 10.2.6 Punctuation and decorations
      7. 10.2.7 Resetting rules for inherited properties
      8. 10.2.8 The hr element
      9. 10.2.9 The fieldset element
    3. 10.3 Replaced elements
      1. 10.3.1 Embedded content
      2. 10.3.2 Images
      3. 10.3.3 Attributes for embedded content and images
      4. 10.3.4 Image maps
      5. 10.3.5 Tool bars
    4. 10.4 Bindings
      1. 10.4.1 Introduction
      2. 10.4.2 The bb element
      3. 10.4.3 The button element
      4. 10.4.4 The datagrid element
      5. 10.4.5 The details element
      6. 10.4.6 The input element as a text entry widget
      7. 10.4.7 The input element as domain-specific widgets
      8. 10.4.8 The input element as a range control
      9. 10.4.9 The input element as a color well
      10. 10.4.10 The input element as a check box and radio button widgets
      11. 10.4.11 The input element as a file upload control
      12. 10.4.12 The input element as a button
      13. 10.4.13 The marquee element
      14. 10.4.14 The meter element
      15. 10.4.15 The progress element
      16. 10.4.16 The select element
      17. 10.4.17 The textarea element
      18. 10.4.18 The keygen element
      19. 10.4.19 The time element
    5. 10.5 Frames and framesets
    6. 10.6 Interactive media
      1. 10.6.1 Links, forms, and navigation
      2. 10.6.2 The mark element
      3. 10.6.3 The title attribute
    7. 10.7 Print media
    8. 10.8 Interaction with CSS
  11. 11 Obsolete features
    1. 11.1 Self-contained features
      1. 11.1.1 The applet element
      2. 11.1.2 The marquee element
    2. 11.2 Other elements and attributes
    3. 11.3 Other DOM APIs
    4. 11.4 Conformance checkers
  12. 12 Things that you can't do with this specification because they are better handled using other technologies that are further described herein
    1. 12.1 Localization
    2. 12.2 Declarative 3D scenes
    3. 12.3 Timers
    4. 12.4 Rendering and the DOM
  13. Index
  14. References
  15. Acknowledgements

1 Introduction

1.1 Background

This section is non-normative.

The World Wide Web's markup language has always been HTML. HTML was primarily designed as a language for semantically describing scientific documents, although its general design and adaptations over the years has enabled it to be used to describe a number of other types of documents.

The main area that has not been adequately addressed by HTML is a vague subject referred to as Web Applications. This specification attempts to rectify this, while at the same time updating the HTML specifications to address issues raised in the past few years.

1.2 Audience

This section is non-normative.

This specification is intended for authors of documents and scripts that use the features defined in this specification, and implementors of tools that are intended to conform to this specification, and individuals wishing to establish the correctness of documents or implementations with respect to the requirements of this specification.

This document is probably not suited to readers who do not already have at least a passing familiarity with Web technologies, as in places it sacrifices clarity for precision, and brevity for completeness. More approachable tutorials and authoring guides can provide a gentler introduction to the topic.

In particular, readers should be familiar with the basics of DOM Core and DOM Events before reading this specification. An understanding of WebIDL, HTTP, XML, Unicode, character encodings, JavaScript, and CSS will be helpful in places but is not essential.

1.3 Scope

This section is non-normative.

This specification is limited to providing a semantic-level markup language and associated semantic-level scripting APIs for authoring accessible pages on the Web ranging from static documents to dynamic applications.

The scope of this specification does not include providing mechanisms for media-specific customization of presentation (although default rendering rules for Web browsers are included at the end of this specification, and several mechanisms for hooking into CSS are provided as part of the language).

The scope of this specification does not include documenting every HTML or DOM feature supported by Web browsers. Browsers support many features that are considered to be very bad for accessibility or that are otherwise inappropriate. For example, the blink element is clearly presentational and authors wishing to cause text to blink should instead use CSS.

The scope of this specification is not to describe an entire operating system. In particular, hardware configuration software, image manipulation tools, and applications that users would be expected to use with high-end workstations on a daily basis are out of scope. In terms of applications, this specification is targeted specifically at applications that would be expected to be used by users on an occasional basis, or regularly but from disparate locations, with low CPU requirements. For instance online purchasing systems, searching systems, games (especially multiplayer online games), public telephone books or address books, communications software (e-mail clients, instant messaging clients, discussion software), document editing software, etc.

1.4 History

This section is non-normative.

Work on HTML5 originally started in late 2003, as a proof of concept to show that it was possible to extend HTML4's forms to provide many of the features that XForms 1.0 introduced, without requiring browsers to implement rendering engines that were incompatible with existing HTML Web pages. At this early stage, while the draft was already publicly available, and input was already being solicited from all sources, the specification was only under Opera Software's copyright.

In early 2004, some of the principles that underlie this effort, as well as an early draft proposal covering just forms-related features, were presented to the W3C jointly by Mozilla and Opera at a workshop discussing the future of Web Applications on the Web. The proposal was rejected on the grounds that the proposal conflicted with the previously chosen direction for the Web's evolution.

Shortly thereafter, Apple, Mozilla, and Opera jointly announced their intent to continue working on the effort. A public mailing list was created, and the drafts were moved to the WHATWG site. The copyright was subsequently amended to be jointly owned by all three vendors, and to allow reuse of the specifications.

In 2006, the W3C expressed interest in the specification, and created a working group chartered to work with the WHATWG on the development of the HTML5 specifications. The working group opened in 2007. Apple, Mozilla, and Opera allowed the W3C to publish the specifications under the W3C copyright, while keeping versions with the less restrictive license on the WHATWG site.

Since then, both groups have been working together.

1.5 Design notes

This section is non-normative.

It must be admitted that many aspects of HTML appear at first glance to be nonsensical and inconsistent.

HTML, its supporting DOM APIs, as well as many of its supporting technologies, have been developed over a period of several decades by a wide array of people with different priorities who, in many cases, did not know of each other's existence.

Features have thus arisen from many sources, and have not always been designed in especially consistent ways. Furthermore, because of the unique characteristics of the Web, implementation bugs have often become de-facto, and now de-jure, standards, as content is often unintentionally written in ways that rely on them before they can be fixed.

Despite all this, efforts have been made to adhere to certain design goals. These are described in the next few subsections.

1.5.1 Serializability of script execution

This section is non-normative.

To avoid exposing Web authors to the complexities of multithreading, the HTML and DOM APIs are designed such that no script can ever detect the simultaneous execution of other scripts. Even with workers, the intent is that the behavior of implementations can be thought of as completely serialising the execution of all scripts in all browsing contexts.

The navigator.getStorageUpdates() method, in this model, is equivalent to allowing other scripts to run while the calling script is blocked.

1.5.2 Compliance with other specifications

This section is non-normative.

HTML5 interacts with and relies on a wide variety of other specifications. In certain circumstances, unfortunately, the desire to be compatible with legacy content has led to HTML5 violating the requirements of these other specifications. Whenever this has occured, the transgressions have been noted as "willful violations".

1.6 Relationships to other specifications

1.6.1 Relationship to HTML 4.01 and DOM2 HTML

This section is non-normative.

This specification represents a new version of HTML4, along with a new version of the associated DOM2 HTML API. Migration from HTML4 to the format and APIs described in this specification should in most cases be straightforward, as care has been taken to ensure that backwards-compatibility is retained. [HTML4] [DOM2HTML]

1.6.2 Relationship to XHTML 1.x

This section is non-normative.

This specification is intended to replace XHTML 1.0 as the normative definition of the XML serialization of the HTML vocabulary. [XHTML10]

While this specification updates the semantics and requirements of the vocabulary defined by XHTML Modularization 1.1 and used by XHTML 1.1, it does not attempt to provide a replacement for the modularization scheme defined and used by those (and other) specifications, and therefore cannot be considered a complete replacement for them. [XHTMLMOD] [XHTML11]

Thus, authors and implementors who do not need such a modularization scheme can consider this specification a replacement for XHTML 1.x, but those who do need such a mechanism are encouraged to continue using the XHTML 1.1 line of specifications.

1.6.3 Relationship to XHTML2 and XForms

This section is non-normative.

XHTML2 defines a new vocabulary with features for hyperlinks, multimedia content, annotating document edits, rich metadata, declarative interactive forms, and describing the semantics of human literary works such as poems and scientific papers. [XHTML2]

XForms similarly defines a new vocabulary with features for complex data entry, such as tax forms or insurance forms.

However, XHTML2 and XForms lack features to express the semantics of many of the non-document types of content often seen on the Web. For instance, they are not well-suited for marking up forum sites, auction sites, search engines, online shops, mapping applications, e-mail applications, word processors, real-time strategy games, and the like.

This specification aims to extend HTML so that it is also suitable in these contexts.

XHTML2, XForms, and this specification all use different namespaces and therefore can all be implemented in the same XML processor.

1.7 HTML vs XHTML

This section is non-normative.

This specification defines an abstract language for describing documents and applications, and some APIs for interacting with in-memory representations of resources that use this language.

The in-memory representation is known as "DOM5 HTML", or "the DOM" for short.

There are various concrete syntaxes that can be used to transmit resources that use this abstract language, two of which are defined in this specification.

The first such concrete syntax is "HTML5". This is the format recommended for most authors. It is compatible with all legacy Web browsers. If a document is transmitted with the MIME type text/html, then it will be processed as an "HTML5" document by Web browsers.

The second concrete syntax uses XML, and is known as "XHTML5". When a document is transmitted with an XML MIME type, such as application/xhtml+xml, then it is processed by an XML processor by Web browsers, and treated as an "XHTML5" document. Authors are reminded that the processing for XML and HTML differs; in particular, even minor syntax errors will prevent an XML document from being rendered fully, whereas they would be ignored in the "HTML5" syntax.

The "DOM5 HTML", "HTML5", and "XHTML5" representations cannot all represent the same content. For example, namespaces cannot be represented using "HTML5", but they are supported in "DOM5 HTML" and "XHTML5". Similarly, documents that use the noscript feature can be represented using "HTML5", but cannot be represented with "XHTML5" and "DOM5 HTML". Comments that contain the string "-->" can be represented in "DOM5 HTML" but not in "HTML5" and "XHTML5". And so forth.

1.8 Structure of this specification

This section is non-normative.

This specification is divided into the following major sections:

Common Infrastructure
The conformance classes, algorithms, definitions, and the common underpinnings of the rest of the specification.
The DOM
Documents are built from elements. These elements form a tree using the DOM. This section defines the features of this DOM, as well as introducing the features common to all elements, and the concepts used in defining elements.
Elements
Each element has a predefined meaning, which is explained in this section. Rules for authors on how to use the element, along with user agent requirements for how to handle each element, are also given.
Web Browsers
HTML documents do not exist in a vacuum — this section defines many of the features that affect environments that deal with multiple pages, links between pages, and running scripts.
User Interaction
HTML documents can provide a number of mechanisms for users to interact with and modify content, which are described in this section.
The Communication APIs
Applications written in HTML often require mechanisms to communicate with remote servers, as well as communicating with other applications from different domains running on the same client.
The Language Syntax
All of these features would be for naught if they couldn't be represented in a serialized form and sent to other people, and so this section defines the syntax of HTML, along with rules for how to parse HTML.

There are also a couple of appendices, defining rendering rules for Web browsers and listing areas that are out of scope for this specification.

1.8.1 How to read this specification

This specification should be read like all other specifications. First, it should be read cover-to-cover, multiple times. Then, it should be read backwards at least once. Then it should be read by picking random sections from the contents list and following all the cross-references.

1.8.2 Typographic conventions

This is a definition, requirement, or explanation.

This is a note.

This is an example.

This is an open issue.

This is a warning.

interface Example {
  // this is an IDL definition
};
variable = object . method( [ optionalArgument ] )

This is a note to authors describing the usage of an interface.

/* this is a CSS fragment */

The defining instance of a term is marked up like this. Uses of that term are marked up like this or like this.

The defining instance of an element, attribute, or API is marked up like this. References to that element, attribute, or API are marked up like this.

Other code fragments are marked up like this.

Variables are marked up like this.

This is an implementation requirement.

2 Common infrastructure

2.1 Terminology

This specification refers to both HTML and XML attributes and DOM attributes, often in the same context. When it is not clear which is being referred to, they are referred to as content attributes for HTML and XML attributes, and DOM attributes for those from the DOM. Similarly, the term "properties" is used for both JavaScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.

The term HTML documents is sometimes used in contrast with XML documents to specifically mean documents that were parsed using an HTML parser (as opposed to using an XML parser or created purely through the DOM).

Generally, when the specification states that a feature applies to HTML or XHTML, it also includes the other. When a feature specifically only applies to one of the two languages, it is called out by explicitly stating that it does not apply to the other format, as in "for HTML, ... (this does not apply to XHTML)".

This specification uses the term document to refer to any use of HTML, ranging from short static documents to long essays or reports with rich multimedia, as well as to fully-fledged interactive applications.

For simplicity, terms such as shown, displayed, and visible might sometimes be used when referring to the way a document is rendered to the user. These terms are not meant to imply a visual medium; they must be considered to apply to other media in equivalent ways.

2.1.1 XML

To ease migration from HTML to XHTML, UAs conforming to this specification will place elements in HTML in the http://www.w3.org/1999/xhtml namespace, at least for the purposes of the DOM and CSS. The term "elements in the HTML namespace", or "HTML elements" for short, when used in this specification, thus refers to both HTML and XHTML elements.

Unless otherwise stated, all elements defined or mentioned in this specification are in the http://www.w3.org/1999/xhtml namespace, and all attributes defined or mentioned in this specification have no namespace (they are in the per-element partition).

When an XML name, such as an attribute or element name, is referred to in the form prefix:localName, as in xml:id or svg:rect, it refers to a name with the local name localName and the namespace given by the prefix, as defined by the following table:

xml
http://www.w3.org/XML/1998/namespace
html
http://www.w3.org/1999/xhtml
svg
http://www.w3.org/2000/svg

Attribute names are said to be XML-compatible if they match the Name production defined in XML, they contain no U+003A COLON (:) characters, and their first three characters are not an ASCII case-insensitive match for the string "xml". [XML]

2.1.2 DOM trees

The term root element, when not explicitly qualified as referring to the document's root element, means the furthest ancestor element node of whatever node is being discussed, or the node itself if it has no ancestors. When the node is a part of the document, then that is indeed the document's root element; however, if the node is not currently part of the document tree, the root element will be an orphaned node.

A node's home subtree is the subtree rooted at that node's root element.

The Document of a Node (such as an element) is the Document that the Node's ownerDocument DOM attribute returns.

An element is said to have been inserted into a document when its root element changes and is now the document's root element. If a Node is in a Document then that Document is always the Node's Document, and the Node's ownerDocument DOM attribute thus always returns that Document.

The term tree order means a pre-order, depth-first traversal of DOM nodes involved (through the parentNode/childNodes relationship).

When it is stated that some element or attribute is ignored, or treated as some other value, or handled as if it was something else, this refers only to the processing of the node after it is in the DOM. A user agent must not mutate the DOM in such situations.

The term text node refers to any Text node, including CDATASection nodes; specifically, any Node with node type TEXT_NODE (3) or CDATA_SECTION_NODE (4). [DOM3CORE]

2.1.3 Scripting

The construction "a Foo object", where Foo is actually an interface, is sometimes used instead of the more accurate "an object implementing the interface Foo".

A DOM attribute is said to be getting when its value is being retrieved (e.g. by author script), and is said to be setting when a new value is assigned to it.

If a DOM object is said to be live, then that means that any attributes returning that object must always return the same object (not a new object each time), and the attributes and methods on that object must operate on the actual underlying data, not a snapshot of the data.

The terms fire and dispatch are used interchangeably in the context of events, as in the DOM Events specifications. [DOM3EVENTS]

2.1.4 Plugins

The term plugin is used to mean any content handler, typically a third-party content handler, for Web content types that are not supported by the user agent natively, or for content types that do not expose a DOM, that supports rendering the content as part of the user agent's interface.

One example of a plugin would be a PDF viewer that is instantiated in a browsing context when the user navigates to a PDF file. This would count as a plugin regardless of whether the party that implemented the PDF viewer component was the same as that which implemented the user agent itself. However, a PDF viewer application that launches separate from the user agent (as opposed to using the same interface) is not a plugin by this definition.

This specification does not define a mechanism for interacting with plugins, as it is expected to be user-agent- and platform-specific. Some UAs might opt to support a plugin mechanism such as the Netscape Plugin API; others might use remote content converters or have built-in support for certain types. [NPAPI]

Browsers should take extreme care when interacting with external content intended for plugins. When third-party software is run with the same privileges as the user agent itself, vulnerabilities in the third-party software become as dangerous as those in the user agent.

2.1.5 Character encodings

An ASCII-compatible character encoding is one that is a superset of US-ASCII (specifically, ANSI_X3.4-1968) for bytes in the set 0x09, 0x0A, 0x0C, 0x0D, 0x20 - 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A, and 0x61 - 0x7A.

2.2 Conformance requirements

All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. For readability, these words do not appear in all uppercase letters in this specification. [RFC2119]

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

This specification describes the conformance criteria for user agents (relevant to implementors) and documents (relevant to authors and authoring tool implementors).

There is no implied relationship between document conformance requirements and implementation conformance requirements. User agents are not free to handle non-conformant documents as they please; the processing model described in this specification applies to implementations regardless of the conformity of the input documents.

User agents fall into several (overlapping) categories with different conformance requirements.

Web browsers and other interactive user agents

Web browsers that support XHTML must process elements and attributes from the HTML namespace found in XML documents as described in this specification, so that users can interact with them, unless the semantics of those elements have been overridden by other specifications.

A conforming XHTML processor would, upon finding an XHTML script element in an XML document, execute the script contained in that element. However, if the element is found within a transformation expressed in XSLT (assuming the user agent also supports XSLT), then the processor would instead treat the script element as an opaque element that forms part of the transform.

Web browsers that support HTML must process documents labeled as text/html as described in this specification, so that users can interact with them.

User agents that support scripting must also be conforming implementations of the IDL fragments in this specification, as described in the WebIDL specification. [WebIDL]

Non-interactive presentation user agents

User agents that process HTML and XHTML documents purely to render non-interactive versions of them must comply to the same conformance criteria as Web browsers, except that they are exempt from requirements regarding user interaction.

Typical examples of non-interactive presentation user agents are printers (static UAs) and overhead displays (dynamic UAs). It is expected that most static non-interactive presentation user agents will also opt to lack scripting support.

A non-interactive but dynamic presentation UA would still execute scripts, allowing forms to be dynamically submitted, and so forth. However, since the concept of "focus" is irrelevant when the user cannot interact with the document, the UA would not need to support any of the focus-related DOM APIs.

User agents with no scripting support

Implementations that do not support scripting (or which have their scripting features disabled entirely) are exempt from supporting the events and DOM interfaces mentioned in this specification. For the parts of this specification that are defined in terms of an events model or in terms of the DOM, such user agents must still act as if events and the DOM were supported.

Scripting can form an integral part of an application. Web browsers that do not support scripting, or that have scripting disabled, might be unable to fully convey the author's intent.

Conformance checkers

Conformance checkers must verify that a document conforms to the applicable conformance criteria described in this specification. Automated conformance checkers are exempt from detecting errors that require interpretation of the author's intent (for example, while a document is non-conforming if the content of a blockquote element is not a quote, conformance checkers running without the input of human judgement do not have to check that blockquote elements only contain quoted material).

Conformance checkers must check that the input document conforms when parsed without a browsing context (meaning that no scripts are run, and that the parser's scripting flag is disabled), and should also check that the input document conforms when parsed with a browsing context in which scripts execute, and that the scripts never cause non-conforming states to occur other than transiently during script execution itself. (This is only a "SHOULD" and not a "MUST" requirement because it has been proven to be impossible. [HALTINGPROBLEM])

The term "HTML5 validator" can be used to refer to a conformance checker that itself conforms to the applicable requirements of this specification.

XML DTDs cannot express all the conformance requirements of this specification. Therefore, a validating XML processor and a DTD cannot constitute a conformance checker. Also, since neither of the two authoring formats defined in this specification are applications of SGML, a validating SGML system cannot constitute a conformance checker either.

To put it another way, there are three types of conformance criteria:

  1. Criteria that can be expressed in a DTD.
  2. Criteria that cannot be expressed by a DTD, but can still be checked by a machine.
  3. Criteria that can only be checked by a human.

A conformance checker must check for the first two. A simple DTD-based validator only checks for the first class of errors and is therefore not a conforming conformance checker according to this specification.

Data mining tools

Applications and tools that process HTML and XHTML documents for reasons other than to either render the documents or check them for conformance should act in accordance to the semantics of the documents that they process.

A tool that generates document outlines but increases the nesting level for each paragraph and does not increase the nesting level for each section would not be conforming.

Authoring tools and markup generators

Authoring tools and markup generators must generate conforming documents. Conformance criteria that apply to authors also apply to authoring tools, where appropriate.

Authoring tools are exempt from the strict requirements of using elements only for their specified purpose, but only to the extent that authoring tools are not yet able to determine author intent.

For example, it is not conforming to use an address element for arbitrary contact information; that element can only be used for marking up contact information for the author of the document or section. However, since an authoring tool is likely unable to determine the difference, an authoring tool is exempt from that requirement.

In terms of conformance checking, an editor is therefore required to output documents that conform to the same extent that a conformance checker will verify.

When an authoring tool is used to edit a non-conforming document, it may preserve the conformance errors in sections of the document that were not edited during the editing session (i.e. an editing tool is allowed to round-trip erroneous content). However, an authoring tool must not claim that the output is conformant if errors have been so preserved.

Authoring tools are expected to come in two broad varieties: tools that work from structure or semantic data, and tools that work on a What-You-See-Is-What-You-Get media-specific editing basis (WYSIWYG).

The former is the preferred mechanism for tools that author HTML, since the structure in the source information can be used to make informed choices regarding which HTML elements and attributes are most appropriate.

However, WYSIWYG tools are legitimate. WYSIWYG tools should use elements they know are appropriate, and should not use elements that they do not know to be appropriate. This might in certain extreme cases mean limiting the use of flow elements to just a few elements, like div, b, i, and span and making liberal use of the style attribute.

All authoring tools, whether WYSIWYG or not, should make a best effort attempt at enabling users to create well-structured, semantically rich, media-independent content.

Some conformance requirements are phrased as requirements on elements, attributes, methods or objects. Such requirements fall into two categories: those describing content model restrictions, and those describing implementation behavior. Those in the former category are requirements on documents and authoring tools. Those in the second category are requirements on user agents.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.

For compatibility with existing content and prior specifications, this specification describes two authoring formats: one based on XML (referred to as XHTML5), and one using a custom format inspired by SGML (referred to as HTML5). Implementations may support only one of these two formats, although supporting both is encouraged.

XHTML documents (XML documents using elements from the HTML namespace) that use the new features described in this specification and that are served over the wire (e.g. by HTTP) must be sent using an XML MIME type such as application/xml or application/xhtml+xml and must not be served as text/html. [RFC3023]

HTML documents, if they are served over the wire (e.g. by HTTP) must be labeled with the text/html MIME type.

The language in this specification assumes that the user agent expands all entity references, and therefore does not include entity reference nodes in the DOM. If user agents do include entity reference nodes in the DOM, then user agents must handle them as if they were fully expanded when implementing this specification. For example, if a requirement talks about an element's child text nodes, then any text nodes that are children of an entity reference that is a child of that element would be used as well. Entity references to unknown entities must be treated as if they contained just an empty text node for the purposes of the algorithms defined in this specification.

2.2.1 Dependencies

This specification relies on several other underlying specifications.

XML

Implementations that support XHTML5 must support some version of XML, as well as its corresponding namespaces specification, because XHTML5 uses an XML serialization with namespaces. [XML] [XMLNAMES]

DOM

The Document Object Model (DOM) is a representation — a model — of a document and its content. The DOM is not just an API; the conformance criteria of HTML implementations are defined, in this specification, in terms of operations on the DOM. [DOM3CORE]

Implementations must support some version of DOM Core and DOM Events, because this specification is defined in terms of the DOM, and some of the features are defined as extensions to the DOM Core interfaces. [DOM3CORE] [DOM3EVENTS]

WebIDL

The IDL fragments in this specification must be interpreted as required for conforming IDL fragments, as described in the Web IDL specification. [WebIDL]

JavaScript

Some parts of the language described by this specification only support JavaScript as the underlying scripting language. [ECMA262]

The term "JavaScript" is used to refer to ECMA262, rather than the official term ECMAScript, since the term JavaScript is more widely known. Similarly, the MIME type used to refer to JavaScript in this specification is text/javascript, since that is the most commonly used type, despite it being an officially obsoleted type according to RFC 4329. [RFC4329]

Media Queries

Implementations must support some version of the Media Queries language. [MQ]

This specification does not require support of any particular network transport protocols, style sheet language, scripting language, or any of the DOM and WebAPI specifications beyond those described above. However, the language described by this specification is biased towards CSS as the styling language, JavaScript as the scripting language, and HTTP as the network protocol, and several features assume that those languages and protocols are in use.

This specification might have certain additional requirements on character encodings, image formats, audio formats, and video formats in the respective sections.

2.2.2 Features defined in other specifications

this section will be removed at some point

Some elements are defined in terms of their DOM textContent attribute. This is an attribute defined on the Node interface in DOM3 Core. [DOM3CORE]

The rules for handling alternative style sheets are defined in the CSS object model specification. [CSSOM]

See http://dev.w3.org/cvsweb/~checkout~/csswg/cssom/Overview.html?content-type=text/html;%20charset=utf-8

2.2.3 Common conformance requirements for APIs exposed to JavaScript

This section will eventually be removed in favor of WebIDL.

A lot of arrays/lists/collections in this spec assume zero-based indexes but use the term "indexth" liberally. We should define those to be zero-based and be clearer about this.

Unless otherwise specified, if a DOM attribute that is a floating point number type (float) is assigned an Infinity or Not-a-Number value, a NOT_SUPPORTED_ERR exception must be raised.

Unless otherwise specified, if a method with an argument that is a floating point number type (float) is passed an Infinity or Not-a-Number value, a NOT_SUPPORTED_ERR exception must be raised.

Unless otherwise specified, if a method is passed fewer arguments than is defined for that method in its IDL definition, a NOT_SUPPORTED_ERR exception must be raised.

Unless otherwise specified, if a method is passed more arguments than is defined for that method in its IDL definition, the excess arguments must be ignored.

2.3 Case-sensitivity and string comparison

This specification defines several comparison operators for strings.

Comparing two strings in a case-sensitive manner means comparing them exactly, code point for code point.

Comparing two strings in an ASCII case-insensitive manner means comparing them exactly, code point for code point, except that the characters in the range U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) and the corresponding characters in the range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z) are considered to also match.

Comparing two strings in a compatibility caseless manner means using the Unicode compatibility caseless match operation to compare the two strings. [UNICODECASE]

Converting a string to uppercase means replacing all characters in the range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z) with the corresponding characters in the range U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).

Converting a string to lowercase means replacing all characters in the range U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) with the corresponding characters in the range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z).

A string pattern is a prefix match for a string s when pattern is not longer than s and truncating s to pattern's length leaves the two strings as matches of each other.

2.4 Common microsyntaxes

There are various places in HTML that accept particular data types, such as dates or numbers. This section describes what the conformance criteria for content in those formats is, and how to parse them.

Need to go through the whole spec and make sure all the attribute values are clearly defined either in terms of microsyntaxes or in terms of other specs, or as "Text" or some such.

2.4.1 Common parser idioms

The space characters, for the purposes of this specification, are U+0020 SPACE, U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).

The White_Space characters are those that have the Unicode property "White_Space". [UNICODE]

Some of the micro-parsers described below follow the pattern of having an input variable that holds the string being parsed, and having a position variable pointing at the next character to parse in input.

For parsers based on this pattern, a step that requires the user agent to collect a sequence of characters means that the following algorithm must be run, with characters being the set of characters that can be collected:

  1. Let input and position be the same variables as those of the same name in the algorithm that invoked these steps.

  2. Let result be the empty string.

  3. While position doesn't point past the end of input and the character at position is one of the characters, append that character to the end of result and advance position to the next character in input.

  4. Return result.

The step skip whitespace means that the user agent must collect a sequence of characters that are space characters. The step skip White_Space characters means that the user agent must collect a sequence of characters that are White_Space characters. In both cases, the collected characters are not used. [UNICODE]

When a user agent is to strip line breaks from a string, the user agent must remove any U+000A LINE FEED (LF) and U+000D CARRIAGE RETURN (CR) characters from that string.

The code-point length of a string is the number of Unicode code points in that string.

2.4.2 Boolean attributes

A number of attributes in HTML5 are boolean attributes. The presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value.

If the attribute is present, its value must either be the empty string or a value that is an ASCII case-insensitive match for the attribute's canonical name, with no leading or trailing whitespace.

The values "true" and "false" are not allowed on boolean attributes. To represent a false value, the attribute has to be omitted altogether.

2.4.3 Keywords and enumerated attributes

Some attributes are defined as taking one of a finite set of keywords. Such attributes are called enumerated attributes. The keywords are each defined to map to a particular state (several keywords might map to the same state, in which case some of the keywords are synonyms of each other; additionally, some of the keywords can be said to be non-conforming, and are only in the specification for historical reasons). In addition, two default states can be given. The first is the invalid value default, the second is the missing value default.

If an enumerated attribute is specified, the attribute's value must be an ASCII case-insensitive match for one of the given keywords that are not said to be non-conforming, with no leading or trailing whitespace.

When the attribute is specified, if its value is an ASCII case-insensitive match for one of the given keywords then that keyword's state is the state that the attribute represents. If the attribute value matches none of the given keywords, but the attribute has an invalid value default, then the attribute represents that state. Otherwise, if the attribute value matches none of the keywords but there is a missing value default state defined, then that is the state represented by the attribute. Otherwise, there is no default, and invalid values must be ignored.

When the attribute is not specified, if there is a missing value default state defined, then that is the state represented by the (missing) attribute. Otherwise, the absence of the attribute means that there is no state represented.

The empty string can be one of the keywords in some cases. For example the contenteditable attribute has two states: true, matching the true keyword and the empty string, false, matching false and all other keywords (it's the invalid value default). It could further be thought of as having a third state inherit, which would be the default when the attribute is not specified at all (the missing value default), but for various reasons that isn't the way this specification actually defines it.

2.4.4 Numbers

2.4.4.1 Non-negative integers

A string is a valid non-negative integer if it consists of one or more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).

A valid non-negative integer represents the number that is represented in base ten by that string of digits.

The rules for parsing non-negative integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return zero, a positive integer, or an error. Leading spaces are ignored. Trailing spaces and any trailing garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 0.

  4. Skip whitespace.

  5. If position is past the end of input, return an error.

  6. If the next character is a U+002B PLUS SIGN character (+), advance position to the next character.

  7. If position is past the end of input, return an error.

  8. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  9. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is not past the end of input, return to the top of step 7 in the overall algorithm (that's the step within which these substeps find themselves).
  10. Return value.

2.4.4.2 Signed integers

A string is a valid integer if it consists of one or more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally prefixed with a U+002D HYPHEN-MINUS ("-") character.

A valid integer without a U+002D HYPHEN-MINUS ("-") prefix represents the number that is represented in base ten by that string of digits. A valid integer with a U+002D HYPHEN-MINUS ("-") prefix represents the number represented in base ten by the string of digits that follows the U+002D HYPHEN-MINUS, subtracted from zero.

The rules for parsing integers are similar to the rules for non-negative integers, and are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return an integer or an error. Leading spaces are ignored. Trailing spaces and trailing garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 0.

  4. Let sign have the value "positive".

  5. Skip whitespace.

  6. If position is past the end of input, return an error.

  7. If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS ("-") character:

    1. Let sign be "negative".
    2. Advance position to the next character.
    3. If position is past the end of input, return an error.
  8. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  9. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is not past the end of input, return to the top of step 9 in the overall algorithm (that's the step within which these substeps find themselves).
  10. If sign is "positive", return value, otherwise return 0-value.

2.4.4.3 Real numbers

A string is a valid floating point number if it consists of:

  1. Optionally, a U+002D HYPHEN-MINUS ("-") character.
  2. A series of one or more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).
  3. Optionally:
    1. A single U+002E FULL STOP (".") character.
    2. A series of one or more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).
  4. Optionally:
    1. Either a U+0065 LATIN SMALL LETTER E character or a U+0045 LATIN CAPITAL LETTER E character.
    2. Optionally, a U+002D HYPHEN-MINUS ("-") character or U+002B PLUS SIGN ("+") character.
    3. A series of one or more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).

A valid floating point number represents the number obtained by multiplying the significand by ten raised to the power of the exponent, where the significand is the first number, interpreted as base ten (including the decimal point and the number after the decimal point, if any, and interpreting the significand as a negative number if the whole string starts with a U+002D HYPHEN-MINUS ("-") character and the number is not zero), and where the exponent is the number after the E, if any (interpreted as a negative number if there is a U+002D HYPHEN-MINUS ("-") character between the E and the number and the number is not zero, or else ignoring a U+002B PLUS SIGN ("+") character between the E and the number if there is one). If there is no E, then the exponent is treated as zero.

The values ±Infinity and NaN are not valid floating point numbers.

The best representation of the floating point number n is the string obtained from applying the JavaScript operator ToString to n.

The rules for parsing floating point number values are as given in the following algorithm. As with the previous algorithms, when this one is invoked, the steps must be followed in the order given, aborting at the first step that returns something. This algorithm will either return a number or an error. Leading spaces are ignored. Trailing spaces and garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 1.

  4. Let divisor have the value 1.

  5. Let exponent have the value 1.

  6. Skip whitespace.

  7. If position is past the end of input, return an error.

  8. If the character indicated by position is a U+002D HYPHEN-MINUS ("-") character:

    1. Change value and divisor to −1.
    2. Advance position to the next character.
    3. If position is past the end of input, return an error.
  9. If the character indicated by position is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  10. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and interpret the resulting sequence as a base-ten integer. Multiply value by that integer.

  11. If position is past the end of input, return value.
  12. If the character indicated by position is a U+002E FULL STOP ("."), run these substeps:

    1. Advance position to the next character.

    2. If position is past the end of input, or if the character indicated by position is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return value.

    3. Fraction loop: Multiply divisor by ten.

    4. Add the value of the current character interpreted as a base-ten digit (0..9) divided by divisor, to value.
    5. Advance position to the next character.

    6. If position is past the end of input, then return value.

    7. If the character indicated by position is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), return to the step labeled fraction loop in these substeps.

  13. If the character indicated by position is a U+0065 LATIN SMALL LETTER E character or a U+0045 LATIN CAPITAL LETTER E character, run these substeps:

    1. Advance position to the next character.

    2. If position is past the end of input, then return value.

    3. If the character indicated by position is a U+002D HYPHEN-MINUS ("-") character:

      1. Change exponent to −1.
      2. Advance position to the next character.
      3. If position is past the end of input, then return value.

      Otherwise, if the character indicated by position is a U+002B PLUS SIGN ("+") character:

      1. Advance position to the next character.
      2. If position is past the end of input, then return value.

    4. If the character indicated by position is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return value.

    5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and interpret the resulting sequence as a base-ten integer. Multiply exponent by that integer.

    6. Multiply value by ten raised to the exponentth power.

  14. Return value.

2.4.4.4 Ratios

The algorithms described in this section are used by the progress and meter elements.

A valid denominator punctuation character is one of the characters from the table below. There is a value associated with each denominator punctuation character, as shown in the table below.

Denominator Punctuation Character Value
U+0025 PERCENT SIGN % 100
U+066A ARABIC PERCENT SIGN ٪ 100
U+FE6A SMALL PERCENT SIGN 100
U+FF05 FULLWIDTH PERCENT SIGN 100
U+2030 PER MILLE SIGN 1000
U+2031 PER TEN THOUSAND SIGN 10000

The steps for finding one or two numbers of a ratio in a string are as follows:

  1. If the string is empty, then return nothing and abort these steps.
  2. Find a number in the string according to the algorithm below, starting at the start of the string.
  3. If the sub-algorithm in step 2 returned nothing or returned an error condition, return nothing and abort these steps.
  4. Set number1 to the number returned by the sub-algorithm in step 2.
  5. Starting with the character immediately after the last one examined by the sub-algorithm in step 2, skip all White_Space characters in the string (this might match zero characters).
  6. If there are still further characters in the string, and the next character in the string is a valid denominator punctuation character, set denominator to that character.
  7. If the string contains any other characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, but denominator was given a value in the step 6, return nothing and abort these steps.
  8. Otherwise, if denominator was given a value in step 6, return number1 and denominator and abort these steps.
  9. Find a number in the string again, starting immediately after the last character that was examined by the sub-algorithm in step 2.
  10. If the sub-algorithm in step 9 returned nothing or an error condition, return number1 and abort these steps.
  11. Set number2 to the number returned by the sub-algorithm in step 9.
  12. Starting with the character immediately after the last one examined by the sub-algorithm in step 9, skip all White_Space characters in the string (this might match zero characters).
  13. If there are still further characters in the string, and the next character in the string is a valid denominator punctuation character, return nothing and abort these steps.
  14. If the string contains any other characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, return nothing and abort these steps.
  15. Otherwise, return number1 and number2.

The algorithm to find a number is as follows. It is given a string and a starting position, and returns either nothing, a number, or an error condition.

  1. Starting at the given starting position, ignore all characters in the given string until the first character that is either a U+002E FULL STOP or one of the ten characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE.
  2. If there are no such characters, return nothing and abort these steps.
  3. Starting with the character matched in step 1, collect all the consecutive characters that are either a U+002E FULL STOP or one of the ten characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, and assign this string of one or more characters to string.
  4. If string consists of just a single U+002E FULL STOP character or if it contains more than one U+002E FULL STOP character then return an error condition and abort these steps.
  5. Parse string according to the rules for parsing floating point number values, to obtain number. This step cannot fail (string is guaranteed to be a valid floating point number).
  6. Return number.
2.4.4.5 Percentages and lengths

The rules for parsing dimension values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return a number greater than or equal to 1.0, or an error; if a number is returned, then it is further categorized as either a percentage or a length.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Skip whitespace.

  4. If position is past the end of input, return an error.

  5. If the next character is a U+002B PLUS SIGN character (+), advance position to the next character.

  6. Collect a sequence of characters that are U+0030 DIGIT ZERO (0) characters, and discard them.

  7. If position is past the end of input, return an error.

  8. If the next character is not one of U+0031 DIGIT ONE (1) .. U+0039 DIGIT NINE (9), then return an error.

  9. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and interpret the resulting sequence as a base-ten integer. Let value be that number.

  10. If position is past the end of input, return value as an integer.

  11. If the next character is a U+002E FULL STOP character (.):

    1. Advance position to the next character.

    2. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return value as an integer.

    3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). Let length be the number of characters collected. Let fraction be the result of interpreting the collected characters as a base-ten integer, and then dividing that number by 10length.

    4. Increment value by fraction.

  12. If position is past the end of input, return value as a length.

  13. If the next character is a U+0025 PERCENT SIGN character (%), return value as a percentage.

  14. Return value as a length.

2.4.4.6 Lists of integers

A valid list of integers is a number of valid integers separated by U+002C COMMA characters, with no other characters (e.g. no space characters). In addition, there might be restrictions on the number of integers that can be given, or on the range of values allowed.

The rules for parsing a list of integers are as follows:

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let numbers be an initially empty list of integers. This list will be the result of this algorithm.

  4. If there is a character in the string input at position position, and it is either a U+0020 SPACE, U+002C COMMA, or U+003B SEMICOLON character, then advance position to the next character in input, or to beyond the end of the string if there are no more characters.

  5. If position points to beyond the end of input, return numbers and abort.

  6. If the character in the string input at position position is a U+0020 SPACE, U+002C COMMA, or U+003B SEMICOLON character, then return to step 4.

  7. Let negated be false.

  8. Let value be 0.

  9. Let started be false. This variable is set to true when the parser sees a number or a U+002D HYPHEN-MINUS ("-") character.

  10. Let got number be false. This variable is set to true when the parser sees a number.

  11. Let finished be false. This variable is set to true to switch parser into a mode where it ignores characters until the next separator.

  12. Let bogus be false.

  13. Parser: If the character in the string input at position position is:

    A U+002D HYPHEN-MINUS character

    Follow these substeps:

    1. If got number is true, let finished be true.
    2. If finished is true, skip to the next step in the overall set of steps.
    3. If started is true, let negated be false.
    4. Otherwise, if started is false and if bogus is false, let negated be true.
    5. Let started be true.
    A character in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. Multiply value by ten.
    3. Add the value of the digit, interpreted in base ten, to value.
    4. Let started be true.
    5. Let got number be true.
    A U+0020 SPACE character
    A U+002C COMMA character
    A U+003B SEMICOLON character

    Follow these substeps:

    1. If got number is false, return the numbers list and abort. This happens if an entry in the list has no digits, as in "1,2,x,4".
    2. If negated is true, then negate value.
    3. Append value to the numbers list.
    4. Jump to step 4 in the overall set of steps.
    A character in the range U+0001 .. U+001F, U+0021 .. U+002B, U+002D .. U+002F, U+003A, U+003C .. U+0040, U+005B .. U+0060, U+007b .. U+007F (i.e. any other non-alphabetic ASCII character)

    Follow these substeps:

    1. If got number is true, let finished be true.
    2. If finished is true, skip to the next step in the overall set of steps.
    3. Let negated be false.
    Any other character

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. Let negated be false.
    3. Let bogus be true.
    4. If started is true, then return the numbers list, and abort. (The value in value is not appended to the list first; it is dropped.)
  14. Advance position to the next character in input, or to beyond the end of the string if there are no more characters.

  15. If position points to a character (and not to beyond the end of input), jump to the big Parser step above.

  16. If negated is true, then negate value.

  17. If got number is true, then append value to the numbers list.

  18. Return the numbers list and abort.

2.4.4.7 Lists of dimensions

The rules for parsing a list of dimensions are as follows. These rules return a list of zero or more pairs consisting of a number and a unit, the unit being one of percentage, relative, and absolute.

  1. Let raw input be the string being parsed.

  2. If the last character in raw input is a U+002C COMMA character (","), then remove that character from raw input.

  3. Split the string raw input on commas. Let raw tokens be the resulting list of tokens.

  4. Let result be an empty list of number/unit pairs.

  5. For each token in raw tokens, run the following substeps:

    1. Let input be the token.

    2. Let position be a pointer into input, initially pointing at the start of the string.

    3. Let value be the number 0.

    4. Let unit be absolute.

    5. If position is past the end of input, set unit to relative and jump to the last substep.

    6. If the character at position is a character in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), interpret the resulting sequence as an integer in base ten, and increment value by that integer.

    7. If the character at position is a U+002E FULL STOP character (.), run these substeps:

      1. Collect a sequence of characters consisting of space characters and characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). Let s be the resulting sequence.

      2. Remove all space characters in s.

      3. If s is not the empty string, run these subsubsteps:

        1. Let length be the number of characters in s (after the spaces were removed).

        2. Let fraction be the result of interpreting s as a base-ten integer, and then dividing that number by 10length.

        3. Increment value by fraction.

    8. Skip whitespace.

    9. If the character at position is a U+0025 PERCENT SIGN (%) character, then set unit to percentage.

      Otherwise, if the character at position is a U+002A ASTERISK character (*), then set unit to relative.

    10. Add an entry to result consisting of the number given by value and the unit given by unit.

  6. Return the list result.

2.4.5 Dates and times

In the algorithms below, the number of days in month month of year year is: 31 if month is 1, 3, 5, 7, 8, 10, or 12; 30 if month is 4, 6, 9, or 11; 29 if month is 2 and year is a number divisible by 400, or if year is a number divisible by 4 but not by 100; and 28 otherwise. This takes into account leap years in the Gregorian calendar. [GREGORIAN]

The digits in the date and time syntaxes defined in this section must be characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, used to express numbers in base ten.

2.4.5.1 Months

A month consists of a specific proleptic Gregorian date with no time-zone information and no date information beyond a year and a month. [GREGORIAN]

A string is a valid month string representing a year year and month month if it consists of the following components in the given order:

  1. Four or more digits, representing year, where year > 0
  2. A U+002D HYPHEN-MINUS character (-)
  3. Two digits, representing the month month, in the range 1 ≤ month ≤ 12

The rules to parse a month string are as follows. This will either return a year and month, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Parse a month component to obtain year and month. If this returns nothing, then fail.

  4. If position is not beyond the end of input, then fail.

  5. Return year and month.

The rules to parse a month component, given an input string and a position, are as follows. This will either return a year and a month, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.

  2. If year is not a number greater than zero, then fail.

  3. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

  4. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the month.

  5. If month is not a number in the range 1 ≤ month ≤ 12, then fail.

  6. Return year and month.

2.4.5.2 Dates

A date consists of a specific proleptic Gregorian date with no time-zone information, consisting of a year, a month, and a day. [GREGORIAN]

A string is a valid date string representing a year year, month month, and day day if it consists of the following components in the given order:

  1. A valid month string, representing year and month
  2. A U+002D HYPHEN-MINUS character (-)
  3. Two digits, representing day, in the range 1 ≤ day ≤ maxday where maxday is the number of days in the month month and year year

The rules to parse a date string are as follows. This will either return a date, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Parse a date component to obtain year, month, and day. If this returns nothing, then fail.

  4. If position is not beyond the end of input, then fail.

  5. Let date be the date with year year, month month, and day day.

  6. Return date.

The rules to parse a date component, given an input string and a position, are as follows. This will either return a year, a month, and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Parse a month component to obtain year and month. If this returns nothing, then fail.

  2. Let maxday be the number of days in month month of year year.

  3. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

  4. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the day.

  5. If day is not a number in the range 1 ≤ month ≤ maxday, then fail.

  6. Return year, month, and day.

2.4.5.3 Times

A time consists of a specific time with no time-zone information, consisting of an hour, a minute, a second, and a fraction of a second.

A string is a valid time string representing an hour hour, a minute minute, and a second second if it consists of the following components in the given order:

  1. Two digits, representing hour, in the range 0 ≤ hour ≤ 23
  2. A U+003A COLON character (:)
  3. Two digits, representing minute, in the range 0 ≤ minute ≤ 59
  4. Optionally (required if second is non-zero):
    1. A U+003A COLON character (:)
    2. Two digits, representing the integer part of second, in the range 0 ≤ s ≤ 59
    3. Optionally (required if second is not an integer):
      1. A 002E FULL STOP character (.)
      2. One or more digits, representing the fractional part of second

The second component cannot be 60 or 61; leap seconds cannot be represented.

The rules to parse a time string are as follows. This will either return a time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.

  4. If position is not beyond the end of input, then fail.

  5. Let time be the time with hour hour, minute minute, and second second.

  6. Return time.

The rules to parse a time component, given an input string and a position, are as follows. This will either return an hour, a minute, and a second, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the hour.

  2. If hour is not a number in the range 0 ≤ hour ≤ 23, then fail.
  3. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.

  4. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the minute.

  5. If minute is not a number in the range 0 ≤ minute ≤ 59, then fail.
  6. Let second be a string with the value "0".

  7. If position is not beyond the end of input and the character at position is a U+003A COLON, then run these substeps:

    1. Advance position to the next character in input.

    2. If position is beyond the end of input, or at the last character in input, or if the next two characters in input starting at position are not two characters both in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then fail.

    3. Collect a sequence of characters that are either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) or U+002E FULL STOP characters. If the collected sequence has more than one U+002E FULL STOP characters, or if the last character in the sequence is a U+002E FULL STOP character, then fail. Otherwise, let the collected string be second instead of its previous value.

  8. Interpret second as a base-ten number (possibly with a fractional part). Let second be that number instead of the string version.

  9. If second is not a number in the range 0 ≤ second < 60, then fail.

  10. Return hour, minute, and second.

2.4.5.4 Local dates and times

A local date and time consists of a specific proleptic Gregorian date, consisting of a year, a month, and a day, and a time, consisting of an hour, a minute, a second, and a fraction of a second, but expressed without a time zone. [GREGORIAN]

A string is a valid local date and time string representing a date and time if it consists of the following components in the given order:

  1. A valid date string representing the date.
  2. A U+0054 LATIN CAPITAL LETTER T character.
  3. A valid time string representing the time.

The rules to parse a local date and time string are as follows. This will either return a date and time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Parse a date component to obtain year, month, and day. If this returns nothing, then fail.

  4. If position is beyond the end of input or if the character at position is not a U+0054 LATIN CAPITAL LETTER T character then fail. Otherwise, move position forwards one character.

  5. Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.

  6. If position is not beyond the end of input, then fail.

  7. Let date be the date with year year, month month, and day day.

  8. Let time be the time with hour hour, minute minute, and second second.

  9. Return date and time.

2.4.5.5 Global dates and times

A global date and time consists of a specific proleptic Gregorian date, consisting of a year, a month, and a day, and a time, consisting of an hour, a minute, a second, and a fraction of a second, expressed with a time zone, consisting of a number of hours and minutes. [GREGORIAN]

A string is a valid global date and time string representing a date, time, and a time-zone offset if it consists of the following components in the given order:

  1. A valid date string representing the date
  2. A U+0054 LATIN CAPITAL LETTER T character
  3. A valid time string representing the time
  4. Either:

This format allows for time zone offsets from -23:59 to +23:59. In practice, however, the range of actual time zones is -12:00 to +14:00, and the minutes component of actual time zones is always either 00, 30, or 45.

The following are some examples of dates written as valid global date and time strings.

"0037-12-13T00:00Z"
Midnight UTC on the birthday of Nero (the Roman Emperor).
"1979-10-14T12:00:00.001-04:00"
One millisecond after noon on October 14th 1979, in the time zone in use on the east coast of North America during daylight saving time.
"8592-01-01T02:09+02:09"
Midnight UTC on the 1st of January, 8592. The time zone associated with that time is two hours and nine minutes ahead of UTC, which is not a real time zone currently, but is nonetheless allowed.

Several things are notable about these dates:

The rules to parse a global date and time string are as follows. This will either return a time in UTC, with associated time-zone information for round tripping or display purposes, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Parse a date component to obtain year, month, and day. If this returns nothing, then fail.

  4. If position is beyond the end of input or if the character at position is not a U+0054 LATIN CAPITAL LETTER T character then fail. Otherwise, move position forwards one character.

  5. Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.

  6. If position is beyond the end of input, then fail.

  7. Parse a time-zone component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.

  8. If position is not beyond the end of input, then fail.

  9. Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes. That moment in time is a moment in the UTC time zone.

  10. Let timezone be timezonehours hours and timezoneminutes minutes from UTC.

  11. Return time and timezone.

The rules to parse a time-zone component, given an input string and a position, are as follows. This will either return time-zone hours and time-zone minutes, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. If the character at position is a U+005A LATIN CAPITAL LETTER Z, then:

    1. Let timezonehours be 0.

    2. Let timezoneminutes be 0.

    3. Advance position to the next character in input.

    Otherwise, if the character at position is either a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:

    1. If the character at position is a U+002B PLUS SIGN ("+"), let sign be "positive". Otherwise, it's a U+002D HYPHEN-MINUS ("-"); let sign be "negative".

    2. Advance position to the next character in input.

    3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the timezonehours.

    4. If timezonehours is not a number in the range 0 ≤ timezonehours ≤ 23, then fail.
    5. If sign is "negative", then negate timezonehours.
    6. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.

    7. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the timezoneminutes.

    8. If timezoneminutes is not a number in the range 0 ≤ timezoneminutes ≤ 59, then fail.
    9. If sign is "negative", then negate timezoneminutes.
  2. Return timezonehours and timezoneminutes.

2.4.5.6 Weeks

A week consists of a week-year number and a week number representing a seven day period. Each week-year in this calendaring system has either 52 weeks or 53 weeks, as defined below. A week is a seven-day period. The week starting on the Gregorian date Monday December 29th 1969 (1969-12-29) is defined as week number 1 in week-year 1970. Consecutive weeks are numbered sequentially. The week before the number 1 week in a week-year is the last week in the previous week-year, and vice versa. [GREGORIAN]

A week-year with a number year that corresponds to a year year in the proleptic Gregorian calendar that has a Thursday as its first day (January 1st), and a week-year year where year is a number divisible by 400, or a number divisible by 4 but not by 100, has 53 weeks. All other week-years have 52 weeks.

The week number of the last day of a week-year with 53 weeks is 53; the week number of the last day of a week-year with 52 weeks is 52.

The week-year number of a particular day can be different than the number of the year that contains that day in the proleptic Gregorian calendar. The first week in a week-year year is the week that contains the first Thursday of the Gregorian year year.

A string is a valid week string representing a week-year year and week week if it consists of the following components in the given order:

  1. Four or more digits, representing year, where year > 0
  2. A U+002D HYPHEN-MINUS character (-)
  3. A U+0057 LATIN CAPITAL LETTER W character
  4. Two digits, representing the week week, in the range 1 ≤ week ≤ maxweek, where maxweek is the week number of the last day of week-year year

The rules to parse a week string are as follows. This will either return a week-year number and week number, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.

  4. If year is not a number greater than zero, then fail.

  5. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

  6. If position is beyond the end of input or if the character at position is not a U+0057 LATIN CAPITAL LETTER W character, then fail. Otherwise, move position forwards one character.

  7. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the week.

  8. Let maxweek be the week number of the last day of year year.

  9. If week is not a number in the range 1 ≤ week ≤ maxweek, then fail.

  10. If position is not beyond the end of input, then fail.

  11. Return the week-year number year and the week number week.

2.4.5.7 Vaguer moments in time

A date or time string consists of either a date, a time, or a global date and time.

A string is a valid date or time string if it is also one of the following:

A string is a valid date or time string in content if it consists of zero or more White_Space characters, followed by a valid date or time string, followed by zero or more further White_Space characters.

The rules to parse a date or time string are as follows. The algorithm is invoked with a flag indicating if the in attribute variant or the in content variant is to be used. The algorithm will either return a date, a time, a global date and time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. For the in content variant: skip White_Space characters.

  4. Set start position to the same position as position.

  5. Set the date present and time present flags to true.

  6. Parse a date component to obtain year, month, and day. If this fails, then set the date present flag to false.

  7. If date present is true, and position is not beyond the end of input, and the character at position is a U+0054 LATIN CAPITAL LETTER T character, then advance position to the next character in input.

    Otherwise, if date present is true, and either position is beyond the end of input or the character at position is not a U+0054 LATIN CAPITAL LETTER T character, then set time present to false.

    Otherwise, if date present is false, set position back to the same position as start position.

  8. If the time present flag is true, then parse a time component to obtain hour, minute, and second. If this returns nothing, then set the time present flag to false.

  9. If both the date present and time present flags are false, then fail.

  10. If the time present flag is true, but position is beyond the end of input, then fail.

  11. If the date present and time present flags are both true, parse a time-zone component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.

  12. For the in content variant: skip White_Space characters.

  13. If position is not beyond the end of input, then fail.

  14. If the date present flag is true and the time present flag is false, then let date be the date with year year, month month, and day day, and return date.

    Otherwise, if the time present flag is true and the date present flag is false, then let time be the time with hour hour, minute minute, and second second, and return time.

    Otherwise, let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes, that moment in time being a moment in the UTC time zone; let timezone be timezonehours hours and timezoneminutes minutes from UTC; and return time and timezone.

2.4.6 Colors

A simple color consists of three 8-bit numbers in the range 0..255, representing the red, green, and blue components of the color respectively, in the sRGB color space. [SRGB]

A string is a valid simple color if it is exactly seven characters long, and the first character is a U+0023 NUMBER SIGN (#) character, and the remaining six characters are all in the range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, with the first two digits representing the red component, the middle two digits representing the green component, and the last two digits representing the blue component, in hexadecimal.

A string is a valid lowercase simple color if it is a valid simple color and doesn't use any characters in the range U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F.

The rules for parsing simple color values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return a simple color or an error.

  1. Let input be the string being parsed.

  2. If input is not exactly seven characters long, then return an error.

  3. If the first character in input is not a U+0023 NUMBER SIGN (#) character, then return an error.

  4. If the last six characters of input are not all in the range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, then return an error.

  5. Let result be a simple color.

  6. Interpret the second and third characters as a hexadecimal number and let the result be the red component of result.

  7. Interpret the fourth and fifth characters as a hexadecimal number and let the result be the green component of result.

  8. Interpret the sixth and seventh characters as a hexadecimal number and let the result be the blue component of result.

  9. Return result.

The rules for serializing simple color values given a simple color are as given in the following algorithm:

  1. Let result be a string consisting of a single U+0023 NUMBER SIGN (#) character.

  2. Convert the red, green, and blue components in turn to two-digit hexadecimal numbers using the digits U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9) and U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, zero-padding if necessary, and append these numbers to result, in the order red, green, blue.

  3. Return result, which will be a valid lowercase simple color.


Some obsolete legacy attributes parse colors in a more complicated manner, using the rules for parsing a legacy color value, which are given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return a simple color or an error.

  1. Let input be the string being parsed.

  2. If input is the empty string, then return an error.

  3. If input is an ASCII case-insensitive match for the string "transparent", then return an error.

  4. If input is an ASCII case-insensitive match for one of the keywords listed in the SVG color keywords or CSS2 System Colors sections of the CSS3 Color specification, then return the simple color corresponding to that keyword. [CSS3COLOR]

  5. If input is four characters long, and the first character in input is a U+0023 NUMBER SIGN (#) character, and the last three characters of input are all in the range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, and U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, then run these substeps:

    1. Let result be a simple color.

    2. Interpret the second character of input as a hexadecimal digit; let the red component of result be the resulting number multiplied by 17.

    3. Interpret the third character of input as a hexadecimal digit; let the green component of result be the resulting number multiplied by 17.

    4. Interpret the fourth character of input as a hexadecimal digit; let the blue component of result be the resulting number multiplied by 17.

    5. Return result.

  6. Replace any characters in input that have a Unicode code point greater than U+FFFF (i.e. any characters that are not in the basic multilingual plane) with the two-character string "00".

  7. If input is longer than 128 characters, truncate input, leaving only the first 128 characters.

  8. If the first character in input is a U+0023 NUMBER SIGN character (#), remove it.

  9. Replace any character in input that is not in the range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, and U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F with the character U+0030 DIGIT ZERO (0).

  10. While input's length is zero or not a multiple of three, append a U+0030 DIGIT ZERO (0) character to input.

  11. Split input into three strings of equal length, to obtain three components. Let length be the length of those components (one third the length of input).

  12. If length is greater than 8, then remove the leading length-8 characters in each component, and let length be 8.

  13. While length is greater than two and the first character in each component is a U+0030 DIGIT ZERO (0) character, remove that character and reduce length by one.

  14. If length is still greater than two, truncate each component, leaving only the first two characters in each.

  15. Let result be a simple color.

  16. Interpret the first component as a hexadecimal number; let the red component of result be the resulting number.

  17. Interpret the second component as a hexadecimal number; let the green component of result be the resulting number.

  18. Interpret the third component as a hexadecimal number; let the blue component of result be the resulting number.

  19. Return result.


The 2D graphics context has a separate color syntax that also handles opacity.

2.4.7 Space-separated tokens

A set of space-separated tokens is a set of zero or more words separated by one or more space characters, where words consist of any string of one or more characters, none of which are space characters.

A string containing a set of space-separated tokens may have leading or trailing space characters.

An unordered set of unique space-separated tokens is a set of space-separated tokens where none of the words are duplicated.

An ordered set of unique space-separated tokens is a set of space-separated tokens where none of the words are duplicated but where the order of the tokens is meaningful.

Sets of space-separated tokens sometimes have a defined set of allowed values. When a set of allowed values is defined, the tokens must all be from that list of allowed values; other values are non-conforming. If no such set of allowed values is provided, then all values are conforming.

When a user agent has to split a string on spaces, it must use the following algorithm:

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let tokens be a list of tokens, initially empty.

  4. Skip whitespace

  5. While position is not past the end of input:

    1. Collect a sequence of characters that are not space characters.

    2. Add the string collected in the previous step to tokens.

    3. Skip whitespace

  6. Return tokens.

When a user agent has to remove a token from a string, it must use the following algorithm:

  1. Let input be the string being modified.

  2. Let token be the token being removed. It will not contain any space characters.

  3. Let output be the output string, initially empty.

  4. Let position be a pointer into input, initially pointing at the start of the string.

  5. If position is beyond the end of input, set the string being modified to output, and abort these steps.

  6. If the character at position is a space character:

    1. Append the character at position to the end of output.

    2. Increment position so it points at the next character in input.

    3. Return to step 5 in the overall set of steps.

  7. Otherwise, the character at position is the first character of a token. Collect a sequence of characters that are not space characters, and let that be s.

  8. If s is exactly equal to token, then:

    1. Skip whitespace (in input).

    2. Remove any space characters currently at the end of output.

    3. If position is not past the end of input, and output is not the empty string, append a single U+0020 SPACE character at the end of output.

  9. Otherwise, append s to the end of output.

  10. Return to step 6 in the overall set of steps.

This causes any occurrences of the token to be removed from the string, and any spaces that were surrounding the token to be collapsed to a single space, except at the start and end of the string, where such spaces are removed.

2.4.8 Comma-separated tokens

A set of comma-separated tokens is a set of zero or more tokens each separated from the next by a single U+002C COMMA character (,), where tokens consist of any string of zero or more characters, neither beginning nor ending with space characters, nor containing any U+002C COMMA characters (,), and optionally surrounded by space characters.

For instance, the string " a ,b,,d d " consists of four tokens: "a", "b", the empty string, and "d d". Leading and trailing whitespace around each token doesn't count as part of the token, and the empty string can be a token.

Sets of comma-separated tokens sometimes have further restrictions on what consists a valid token. When such restrictions are defined, the tokens must all fit within those restrictions; other values are non-conforming. If no such restrictions are specified, then all values are conforming.

When a user agent has to split a string on commas, it must use the following algorithm:

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let tokens be a list of tokens, initially empty.

  4. Token: If position is past the end of input, jump to the last step.

  5. Collect a sequence of characters that are not U+002C COMMA characters (,). Let s be the resulting sequence (which might be the empty string).

  6. Remove any leading or trailing sequence of space characters from s.

  7. Add s to tokens.

  8. If position is not past the end of input, then the character at position is a U+002C COMMA character (,); advance position past that character.

  9. Jump back to the step labeled token.

  10. Return tokens.

2.4.9 References

A valid hash-name reference to an element of type type is a string consisting of a U+0023 NUMBER SIGN (#) character followed by a string which exactly matches the value of the name attribute of an element in the document with type type.

The rules for parsing a hash-name reference to an element of type type are as follows:

  1. If the string being parsed does not contain a U+0023 NUMBER SIGN character, or if the first such character in the string is the last character in the string, then return null and abort these steps.

  2. Let s be the string from the character immediately after the first U+0023 NUMBER SIGN character in the string being parsed up to the end of that string.

  3. Return the first element of type type that has an id attribute whose value is a case-sensitive match for s or a name attribute whose value is a compatibility caseless match for s.

2.5 URLs

This specification defines the term URL, and defines various algorithms for dealing with URLs, because for historical reasons the rules defined by the URI and IRI specifications are not a complete description of what HTML user agents need to implement to be compatible with Web content.

2.5.1 Terminology

A URL is a string used to identify a resource.

A URL is a valid URL if at least one of the following conditions holds:

A URL has an associated URL character encoding, determined as follows:

If the URL came from a script (e.g. as an argument to a method)
The URL character encoding is the script's URL character encoding.
If the URL came from a DOM node (e.g. from an element)
The node has a Document, and the URL character encoding is the document's character encoding.
If the URL had a character encoding defined when the URL was created or defined
The URL character encoding is as defined.

The term "URL" in this specification is used in a manner distinct from the precise technical meaning it is given in RFC 3986. Readers familiar with that RFC will find it easier to read this specification if they pretend the term "URL" as used herein is really called something else altogether. This is a willful violation of RFC 3986. RFC3986

2.5.2 Parsing URLs

To parse a URL url into its component parts, the user agent must use the following steps:

  1. Strip leading and trailing space characters from url.

  2. Parse url in the manner defined by RFC 3986, with the following exceptions:

    • Add all characters with code points less than or equal to U+0020 or greater than or equal to U+007F to the <unreserved> production.
    • Add the characters U+0022, U+003C, U+003E, U+005B .. U+005E, U+0060, and U+007B .. U+007D to the <unreserved> production.
    • Add a single U+0025 PERCENT SIGN character as a second alternative way of matching the <pct-encoded> production, except when the <pct-encoded> is used in the <reg-name> production.
    • Add the U+0023 NUMBER SIGN character to the characters allowed in the <fragment> production.
  3. If url doesn't match the <URI-reference> production, even after the above changes are made to the ABNF definitions, then parsing the URL fails with an error. [RFC3986]

    Otherwise, parsing url was successful; the components of the URL are substrings of url defined as follows:

    <scheme>

    The substring matched by the <scheme> production, if any.

    <host>

    The substring matched by the <host> production, if any.

    <port>

    The substring matched by the <port> production, if any.

    <hostport>

    If there is a <scheme> component and a <port> component and the port given by the <port> component is different than the default port defined for the protocol given by the <scheme> component, then <hostport> is the substring that starts with the substring matched by the <host> production and ends with the substring matched by the <port> production, and includes the colon in between the two. Otherwise, it is the same as the <host> component.

    <path>

    The substring matched by one of the following productions, if one of them was matched:

    • <path-abempty>
    • <path-absolute>
    • <path-noscheme>
    • <path-rootless>
    • <path-empty>
    <query>

    The substring matched by the <query> production, if any.

    <fragment>

    The substring matched by the <fragment> production, if any.

    <host-specific>

    The substring that follows the substring matched by the <authority> production, or the whole string if the <authority> production wasn't matched.

These parsing rules are a willful violation of RFC 3986 and RFC 3987 to handle legacy content. RFC3986 RFC3987

2.5.3 Resolving URLs

To resolve a URL to an absolute URL relative to either another absolute URL or an element, the user agent must use the following steps. Resolving a URL can result in an error, in which case the URL is not resolvable.

  1. Let url be the URL being resolved.

  2. Let encoding be the URL character encoding.

  3. If encoding is UTF-16, then change it to UTF-8.

  4. If the algorithm was invoked with an absolute URL to use as the base URL, let base be that absolute URL.

    Otherwise, let base be the base URI of the element, as defined by the XML Base specification, with the base URI of the document entity being defined as the document base URL of the Document that owns the element. [XMLBASE]

    For the purposes of the XML Base specification, user agents must act as if all Document objects represented XML documents.

    It is possible for xml:base attributes to be present even in HTML fragments, as such attributes can be added dynamically using script. (Such scripts would not be conforming, however, as xml:base attributes are not allowed in HTML documents.)

    The document base URL of a Document is the absolute URL obtained by running these substeps:

    1. Let fallback base url be the document's address.

    2. If fallback base url is about:blank, and the Document's browsing context has a creator browsing context, then let fallback base url be the document base URL of the creator Document instead.

    3. If there is no base element that is both a child of the head element and has an href attribute, then the document base URL is fallback base url.

    4. Otherwise, let url be the value of the href attribute of the first such element.

    5. Resolve url relative to fallback base url (thus, the base href attribute isn't affected by xml:base attributes).

    6. The document base URL is the result of the previous step if it was successful; otherwise it is fallback base url.

  5. Parse url into its component parts.

  6. If parsing url resulted in a <host> component, then replace the matching substring of url with the string that results from expanding any sequences of percent-encoded octets in that component that are valid UTF-8 sequences into Unicode characters as defined by UTF-8.

    If any percent-encoded octets in that component are not valid UTF-8 sequences, then return an error and abort these steps.

    Apply the IDNA ToASCII algorithm to the matching substring, with both the AllowUnassigned and UseSTD3ASCIIRules flags set. Replace the matching substring with the result of the ToASCII algorithm.

    If ToASCII fails to convert one of the components of the string, e.g. because it is too long or because it contains invalid characters, then return an error and abort these steps. [RFC3490]

  7. If parsing url resulted in a <path> component, then replace the matching substring of url with the string that results from applying the following steps to each character other than U+0025 PERCENT SIGN (%) that doesn't match the original <path> production defined in RFC 3986:

    1. Encode the character into a sequence of octets as defined by UTF-8.
    2. Replace the character with the percent-encoded form of those octets. [RFC3986]

    For instance if url was "//example.com/a^b☺c%FFd%z/?e", then the <path> component's substring would be "/a^b☺c%FFd%z/" and the two characters that would have to be escaped would be "^" and "". The result after this step was applied would therefore be that url now had the value "//example.com/a%5Eb%E2%98%BAc%FFd%z/?e".

  8. If parsing url resulted in a <query> component, then replace the matching substring of url with the string that results from applying the following steps to each character other than U+0025 PERCENT SIGN (%) that doesn't match the original <query> production defined in RFC 3986:

    1. If the character in question cannot be expressed in the encoding encoding, then replace it with a single 0x3F octet (an ASCII question mark) and skip the remaining substeps for this character.
    2. Encode the character into a sequence of octets as defined by the encoding encoding.
    3. Replace the character with the percent-encoded form of those octets. [RFC3986]
  9. Apply the algorithm described in RFC 3986 section 5.2 Relative Resolution, using url as the potentially relative URI reference (R), and base as the base URI (Base). [RFC3986]

  10. Apply any relevant conformance criteria of RFC 3986 and RFC 3987, returning an error and aborting these steps if appropriate. [RFC3986] [RFC3987]

    For instance, if an absolute URI that would be returned by the above algorithm violates the restrictions specific to its scheme, e.g. a data: URI using the "//" server-based naming authority syntax, then user agents are to treat this as an error instead.

  11. Let result be the target URI (T) returned by the Relative Resolution algorithm.

  12. If result uses a scheme with a server-based naming authority, replace all U+005C REVERSE SOLIDUS (\) characters in result with U+002F SOLIDUS (/) characters.

  13. Return result.

A URL is an absolute URL if resolving it results in the same URL without an error.

2.5.4 Dynamic changes to base URLs

When an xml:base attribute changes, the attribute's element, and all descendant elements, are affected by a base URL change.

When a document's document base URL changes, all elements in that document are affected by a base URL change.

When an element is moved from one document to another, if the two documents have different base URLs, then that element and all its descendants are affected by a base URL change.

When an element is affected by a base URL change, it must act as described in the following list:

If the element is a hyperlink element

If the absolute URL identified by the hyperlink is being shown to the user, or if any data derived from that URL is affecting the display, then the href attribute should be re-resolved relative to the element and the UI updated appropriately.

For example, the CSS :link/:visited pseudo-classes might have been affected.

If the hyperlink has a ping attribute and its absolute URL(s) are being shown to the user, then the ping attribute's tokens should be re-resolved relative to the element and the UI updated appropriately.

If the element is a blockquote, q, ins, or del element with a cite attribute

If the absolute URL identified by the cite attribute is being shown to the user, or if any data derived from that URL is affecting the display, then the URL should be re-resolved relative to the element and the UI updated appropriately.

Otherwise

The element is not directly affected.

Changing the base URL doesn't affect the image displayed by img elements, although subsequent accesses of the src DOM attribute from script will return a new absolute URL that might no longer correspond to the image being shown.

2.5.5 Interfaces for URL manipulation

An interface that has a complement of URL decomposition attributes will have seven attributes with the following definitions:

           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;
o . protocol [ = value ]

Returns the current scheme of the underlying URL.

Can be set, to change the underlying URL's scheme.

o . host [ = value ]

Returns the current host and port (if it's not the default port) in the underlying URL.

Can be set, to change the underlying URL's host and port.

The host and the port are separated by a colon. The port part, if omitted, will be assumed to be the current scheme's default port.

o . hostname [ = value ]

Returns the current host in the underlying URL.

Can be set, to change the underlying URL's host.

o . port [ = value ]

Returns the current port in the underlying URL.

Can be set, to change the underlying URL's port.

o . pathname [ = value ]

Returns the current path in the underlying URL.

Can be set, to change the underlying URL's path.

o . search [ = value ]

Returns the current query component in the underlying URL.

Can be set, to change the underlying URL's query component.

o . hash [ = value ]

Returns the current fragment identifier in the underlying URL.

Can be set, to change the underlying URL's fragment identifier.


The attributes defined to be URL decomposition attributes must act as described for the attributes with the same corresponding names in this section.

In addition, an interface with a complement of URL decomposition attributes will define an input, which is a URL that the attributes act on, and a common setter action, which is a set of steps invoked when any of the attributes' setters are invoked.

The seven URL decomposition attributes have similar requirements.

On getting, if the input is an absolute URL that fulfills the condition given in the "getter condition" column corresponding to the attribute in the table below, the user agent must return the part of the input URL given in the "component" column, with any prefixes specified in the "prefix" column appropriately added to the start of the string and any suffixes specified in the "suffix" column appropriately added to the end of the string. Otherwise, the attribute must return the empty string.

On setting, the new value must first be mutated as described by the "setter preprocessor" column, then mutated by %-escaping any characters in the new value that are not valid in the relevant component as given by the "component" column. Then, if the input is an absolute URL and the resulting new value fulfills the condition given in the "setter condition" column, the user agent must make a new string output by replacing the component of the URL given by the "component" column in the input URL with the new value; otherwise, the user agent must let output be equal to the input. Finally, the user agent must invoke the common setter action with the value of output.

When replacing a component in the URL, if the component is part of an optional group in the URL syntax consisting of a character followed by the component, the component (including its prefix character) must be included even if the new value is the empty string.

The previous paragraph applies in particular to the ":" before a <port> component, the "?" before a <query> component, and the "#" before a <fragment> component.

For the purposes of the above definitions, URLs must be parsed using the URL parsing rules defined in this specification.

Attribute Component Getter Condition Prefix Suffix Setter Preprocessor Setter Condition
protocol <scheme> U+003A COLON (":") Remove all trailing U+003A COLON (":") characters The new value is not the empty string
host <hostport> input is hierarchical and uses a server-based naming authority The new value is not the empty string and input is hierarchical and uses a server-based naming authority
hostname <host> input is hierarchical and uses a server-based naming authority Remove all leading U+002F SOLIDUS ("/") characters The new value is not the empty string and input is hierarchical and uses a server-based naming authority
port <port> input is hierarchical, uses a server-based naming authority, and contained a <port> component (possibly an empty one) Remove any characters in the new value that are not in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE. If the resulting string is empty, set it to a single U+0030 DIGIT ZERO character ('0'). input is hierarchical and uses a server-based naming authority
pathname <path> input is hierarchical If it has no leading U+002F SOLIDUS ("/") character, prepend a U+002F SOLIDUS ("/") character to the new value
search <query> input is hierarchical, and contained a <query> component (possibly an empty one) U+003F QUESTION MARK ("?") Remove one leading U+003F QUESTION MARK ("?") character, if any
hash <fragment> input contained a <fragment> component (possibly an empty one) U+0023 NUMBER SIGN ("#") Remove one leading U+0023 NUMBER SIGN ("#") character, if any

The table below demonstrates how the getter condition for search results in different results depending on the exact original syntax of the URL:

Input URL search value Explanation
http://example.com/ empty string No <query> component in input URL.
http://example.com/? ? There is a <query> component, but it is empty. The question mark in the resulting value is the prefix.
http://example.com/?test ?test The <query> component has the value "test".
http://example.com/?test# ?test The (empty) <fragment> component is not part of the <query> component.

2.6 Fetching resources

When a user agent is to fetch a resource, the following steps must be run:

  1. If the resource is identified by the URL about:blank, then return the empty string and abort these steps.

  2. Perform the remaining steps asynchronously.

  3. If the resource is identified by an absolute URL, and the resource is to be obtained using a idempotent action (such as an HTTP GET or equivalent), and it is already being downloaded for other reasons (e.g. another invocation of this algorithm), and the user agent is configured such that it is to reuse the data from the existing download instead of initiating a new one, then use the results of the existing download instead of starting a new one.

    Otherwise, at a time convenient to the user and the user agent, download (or otherwise obtain) the resource, applying the semantics of the relevant specifications (e.g. performing an HTTP GET or POST operation, or reading the file from disk, following redirects, dereferencing javascript: URLs, etc).

  4. If there are cookies to be set, then the user agent must run the following substeps:

    1. Wait until ownership of the storage mutex can be taken by this instance of the fetching algorithm.

    2. Take ownership of the storage mutex.

    3. Update the cookies. [COOKIES]

    4. Release the storage mutex so that it is once again free.

  5. When the resource is available, or if there is an error of some description, queue a task that uses the resource as appropriate. If the resource can be processed incrementally, as, for instance, with a progressively interlaced JPEG or an HTML file, additional tasks may be queued to process the data as it is downloaded. The task source for these tasks is the networking task source.

The application cache processing model introduces some changes to the networking model to handle the returning of cached resources.

The navigation processing model handles redirects itself, overriding the redirection handling that would be done by the fetching algorithm.

Whether the type sniffing rules apply to the fetched resource depends on the algorithm that invokes the rules — they are not always applicable.

2.6.1 Protocol concepts

User agents can implement a variety of transfer protocols, but this specification mostly defines behavior in terms of HTTP. [HTTP]

The HTTP GET method is equivalent to the default retrieval action of the protocol. For example, RETR in FTP. Such actions are idempotent and safe, in HTTP terms.

The HTTP response codes are equivalent to statuses in other protocols that have the same basic meanings. For example, a "file not found" error is equivalent to a 404 code, a server error is equivalent to a 5xx code, and so on.

The HTTP headers are equivalent to fields in other protocols that have the same basic meaning. For example, the HTTP authentication headers are equivalent to the authentication aspects of the FTP protocol.

If there are any specific questions with what should be considered equivalent to what, let me know, and I'll make it more explicit for those cases.

Anything in this specification that refers to HTTP also applies to HTTP-over-TLS, as represented by URLs representing the https scheme.

User agents should report certificate errors to the user and must either refuse to download resources sent with erroneous certificates or must act as if such resources were in fact served with no encryption.

Not doing so can result in users not noticing man-in-the-middle attacks.

If a user connects to a server with a self-signed certificate, the user agent could allow the connection but just act as if there had been no encryption. If the user agent instead allowed the user to override the problem and then displayed the page as if it was fully and safely encrypted, the user could be easily tricked into accepting man-in-the-middle connections.

If a user connects to a server with full encryption, but the page then refers to an external resource that has an expired certificate, then the user agent will act as if the resource was unavailable, possibly also reporting the problem to the user. If the user agent instead allowed the resource to be used, then an attacker could just look for "secure" sites that used resources from a different host and only apply man-in-the-middle attacks to that host, for example taking over scripts in the page.

2.7 Determining the type of a resource

It is imperative that the rules in this section be followed exactly. When a user agent uses different heuristics for content type detection than the server expects, security problems can occur. For example, if a server believes that the client will treat a contributed file as an image (and thus treat it as benign), but a Web browser believes the content to be HTML (and thus execute any scripts contained therein), the end user can be exposed to malicious content, making the user vulnerable to cookie theft attacks and other cross-site scripting attacks.

2.7.1 Content-Type metadata

What explicit Content-Type metadata is associated with the resource (the resource's type information) depends on the protocol that was used to fetch the resource.

For HTTP resources, only the first Content-Type HTTP header, if any, contributes any type information; the explicit type of the resource is then the value of that header, interpreted as described by the HTTP specifications. If the Content-Type HTTP header is present but the value of the first such header cannot be interpreted as described by the HTTP specifications (e.g. because its value doesn't contain a U+002F SOLIDUS ('/') character), then the resource has no type information (even if there are multiple Content-Type HTTP headers and one of the other ones is syntactically correct). [HTTP]

For resources fetched from the file system, user agents should use platform-specific conventions, e.g. operating system extension/type mappings.

Extensions must not be used for determining resource types for resources fetched over HTTP.

For resources fetched over most other protocols, e.g. FTP, there is no type information.

The algorithm for extracting an encoding from a Content-Type, given a string s, is as follows. It either returns an encoding or nothing.

  1. Find the first seven characters in s that are an ASCII case-insensitive match for the word "charset". If no such match is found, return nothing.

  2. Skip any U+0009, U+000A, U+000C, U+000D, or U+0020 characters that immediately follow the word 'charset' (there might not be any).

  3. If the next character is not a U+003D EQUALS SIGN ('='), return nothing.

  4. Skip any U+0009, U+000A, U+000C, U+000D, or U+0020 characters that immediately follow the equals sign (there might not be any).

  5. Process the next character as follows:

    If it is a U+0022 QUOTATION MARK ('"') and there is a later U+0022 QUOTATION MARK ('"') in s
    If it is a U+0027 APOSTROPHE ("'") and there is a later U+0027 APOSTROPHE ("'") in s

    Return the string between this character and the next earliest occurrence of this character.

    If it is an unmatched U+0022 QUOTATION MARK ('"')
    If it is an unmatched U+0027 APOSTROPHE ("'")
    If there is no next character

    Return nothing.

    Otherwise

    Return the string from this character to the first U+0009, U+000A, U+000C, U+000D, U+0020, or U+003B character or the end of s, whichever comes first.

The above algorithm is a willful violation of the HTTP specification. [HTTP]

2.7.2 Content-Type sniffing: Web pages

The sniffed type of a resource must be found as follows:

  1. If the user agent is configured to strictly obey Content-Type headers for this resource, then jump to the last step in this set of steps.

  2. If the resource was fetched over an HTTP protocol and there is an HTTP Content-Type header and the value of the first such header has bytes that exactly match one of the following lines:

    Bytes in Hexadecimal Textual representation
    74 65 78 74 2f 70 6c 61 69 6e text/plain
    74 65 78 74 2f 70 6c 61 69 6e 3b 20 63 68 61 72 73 65 74 3d 49 53 4f 2d 38 38 35 39 2d 31 text/plain; charset=ISO-8859-1
    74 65 78 74 2f 70 6c 61 69 6e 3b 20 63 68 61 72 73 65 74 3d 69 73 6f 2d 38 38 35 39 2d 31 text/plain; charset=iso-8859-1
    74 65 78 74 2f 70 6c 61 69 6e 3b 20 63 68 61 72 73 65 74 3d 55 54 46 2d 38 text/plain; charset=UTF-8

    ...then jump to the text or binary section below.

  3. Let official type be the type given by the Content-Type metadata for the resource, ignoring parameters. If there is no such type, jump to the unknown type step below. Comparisons with this type, as defined by MIME specifications, are done in an ASCII case-insensitive manner. [RFC2046]

  4. If official type is "unknown/unknown" or "application/unknown", jump to the unknown type step below.

  5. If official type ends in "+xml", or if it is either "text/xml" or "application/xml", then the sniffed type of the resource is official type; return that and abort these steps.

  6. If official type is an image type supported by the user agent (e.g. "image/png", "image/gif", "image/jpeg", etc), then jump to the images section below, passing it the official type.

  7. If official type is "text/html", then jump to the feed or HTML section below.

  8. The sniffed type of the resource is official type.

2.7.3 Content-Type sniffing: text or binary

  1. The user agent may wait for 512 or more bytes of the resource to be available.

  2. Let n be the smaller of either 512 or the number of bytes already available.

  3. If n is 4 or more, and the first bytes of the resource match one of the following byte sets:

    Bytes in Hexadecimal Description
    FE FF UTF-16BE BOM
    FF FE UTF-16LE BOM
    EF BB BF UTF-8 BOM

    ...then the sniffed type of the resource is "text/plain". Abort these steps.

  4. If none of the first n bytes of the resource are binary data bytes then the sniffed type of the resource is "text/plain". Abort these steps.

  5. If the first bytes of the resource match one of the byte sequences in the "pattern" column of the table in the unknown type section below, ignoring any rows whose cell in the "security" column says "scriptable" (or "n/a"), then the sniffed type of the resource is the type given in the corresponding cell in the "sniffed type" column on that row; abort these steps.

    It is critical that this step not ever return a scriptable type (e.g. text/html), as otherwise that would allow a privilege escalation attack.

  6. Otherwise, the sniffed type of the resource is "application/octet-stream".

Bytes covered by the following ranges are binary data bytes:

2.7.4 Content-Type sniffing: unknown type

  1. The user agent may wait for 512 or more bytes of the resource to be available.

  2. Let stream length be the smaller of either 512 or the number of bytes already available.

  3. For each row in the table below:

    If the row has no "WS" bytes:
    1. Let pattern length be the length of the pattern (number of bytes described by the cell in the second column of the row).
    2. If stream length is smaller than pattern length then skip this row.
    3. Apply the "and" operator to the first pattern length bytes of the resource and the given mask (the bytes in the cell of first column of that row), and let the result be the data.
    4. If the bytes of the data matches the given pattern bytes exactly, then the sniffed type of the resource is the type given in the cell of the third column in that row; abort these steps.
    If the row has a "WS" byte:
    1. Let indexpattern be an index into the mask and pattern byte strings of the row.

    2. Let indexstream be an index into the byte stream being examined.

    3. Loop: If indexstream points beyond the end of the byte stream, then this row doesn't match, skip this row.

    4. Examine the indexstreamth byte of the byte stream as follows:

      If the indexpatternth byte of the pattern is a normal hexadecimal byte and not a "WS" byte:

      If the "and" operator, applied to the indexstreamth byte of the stream and the indexpatternth byte of the mask, yield a value different that the indexpatternth byte of the pattern, then skip this row.

      Otherwise, increment indexpattern to the next byte in the mask and pattern and indexstream to the next byte in the byte stream.

      Otherwise, if the indexpatternth byte of the pattern is a "WS" byte:

      "WS" means "whitespace", and allows insignificant whitespace to be skipped when sniffing for a type signature.

      If the indexstreamth byte of the stream is one of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0C (ASCII FF), 0x0D (ASCII CR), or 0x20 (ASCII space), then increment only the indexstream to the next byte in the byte stream.

      Otherwise, increment only the indexpattern to the next byte in the mask and pattern.

    5. If indexpattern does not point beyond the end of the mask and pattern byte strings, then jump back to the loop step in this algorithm.

    6. Otherwise, the sniffed type of the resource is the type given in the cell of the third column in that row; abort these steps.

  4. If none of the first n bytes of the resource are binary data bytes then the sniffed type of the resource is "text/plain". Abort these steps.

  5. Otherwise, the sniffed type of the resource is "application/octet-stream".

The table used by the above algorithm is:

Bytes in Hexadecimal Sniffed type Security Comment
Mask Pattern
FF FF DF DF DF DF DF DF DF FF DF DF DF DF 3C 21 44 4F 43 54 59 50 45 20 48 54 4D 4C text/html Scriptable The string "<!DOCTYPE HTML" in US-ASCII or compatible encodings, case-insensitively.
FF FF DF DF DF DF WS 3C 48 54 4D 4C text/html Scriptable The string "<HTML" in US-ASCII or compatible encodings, case-insensitively, possibly with leading spaces.
FF FF DF DF DF DF WS 3C 48 45 41 44 text/html Scriptable The string "<HEAD" in US-ASCII or compatible encodings, case-insensitively, possibly with leading spaces.
FF FF DF DF DF DF DF DF WS 3C 53 43 52 49 50 54 text/html Scriptable The string "<SCRIPT" in US-ASCII or compatible encodings, case-insensitively, possibly with leading spaces.
FF FF FF FF FF 25 50 44 46 2D application/pdf Scriptable The string "%PDF-", the PDF signature.
FF FF FF FF FF FF FF FF FF FF FF 25 21 50 53 2D 41 64 6F 62 65 2D application/postscript Safe The string "%!PS-Adobe-", the PostScript signature.
FF FF 00 00 FE FF 00 00 text/plain n/a UTF-16BE BOM
FF FF 00 00 FF FF 00 00 text/plain n/a UTF-16LE BOM
FF FF FF 00 EF BB BF 00 text/plain n/a UTF-8 BOM
FF FF FF FF FF FF 47 49 46 38 37 61 image/gif Safe The string "GIF87a", a GIF signature.
FF FF FF FF FF FF 47 49 46 38 39 61 image/gif Safe The string "GIF89a", a GIF signature.
FF FF FF FF FF FF FF FF 89 50 4E 47 0D 0A 1A 0A image/png Safe The PNG signature.
FF FF FF FF D8 FF image/jpeg Safe A JPEG SOI marker followed by the first byte of another marker.
FF FF 42 4D image/bmp Safe The string "BM", a BMP signature.
FF FF FF FF 00 00 01 00 image/vnd.microsoft.icon Safe A 0 word following by a 1 word, a Windows Icon file format signature.

I'd like to add types like MPEG, AVI, Flash, Java, etc, to the above table.

User agents may support further types if desired, by implicitly adding to the above table. However, user agents should not use any other patterns for types already mentioned in the table above, as this could then be used for privilege escalation (where, e.g., a server uses the above table to determine that content is not HTML and thus safe from XSS attacks, but then a user agent detects it as HTML anyway and allows script to execute).

The column marked "security" is used by the algorithm in the "text or binary" section, to avoid sniffing text/plain content as a type that can be used for a privilege escalation attack.

2.7.5 Content-Type sniffing: image

If the resource's official type is "image/svg+xml", then the sniffed type of the resource is its official type (an XML type).

Otherwise, if the first bytes of the resource match one of the byte sequences in the first column of the following table, then the sniffed type of the resource is the type given in the corresponding cell in the second column on the same row:

Bytes in Hexadecimal Sniffed type Comment
47 49 46 38 37 61 image/gif The string "GIF87a", a GIF signature.
47 49 46 38 39 61 image/gif The string "GIF89a", a GIF signature.
89 50 4E 47 0D 0A 1A 0A image/png The PNG signature.
FF D8 FF image/jpeg A JPEG SOI marker followed by the first byte of another marker.
42 4D image/bmp The string "BM", a BMP signature.
00 00 01 00 image/vnd.microsoft.icon A 0 word following by a 1 word, a Windows Icon file format signature.

Otherwise, the sniffed type of the resource is the same as its official type.

2.7.6 Content-Type sniffing: feed or HTML

  1. The user agent may wait for 512 or more bytes of the resource to be available.

  2. Let s be the stream of bytes, and let s[i] represent the byte in s with position i, treating s as zero-indexed (so the first byte is at i=0).

  3. If at any point this algorithm requires the user agent to determine the value of a byte in s which is not yet available, or which is past the first 512 bytes of the resource, or which is beyond the end of the resource, the user agent must stop this algorithm, and assume that the sniffed type of the resource is "text/html".

    User agents are allowed, by the first step of this algorithm, to wait until the first 512 bytes of the resource are available.

  4. Initialize pos to 0.

  5. If s[0] is 0xEF, s[1] is 0xBB, and s[2] is 0xBF, then set pos to 3. (This skips over a leading UTF-8 BOM, if any.)

  6. Loop start: Examine s[pos].

    If it is 0x09 (ASCII tab), 0x20 (ASCII space), 0x0A (ASCII LF), or 0x0D (ASCII CR)
    Increase pos by 1 and repeat this step.
    If it is 0x3C (ASCII "<")
    Increase pos by 1 and go to the next step.
    If it is anything else
    The sniffed type of the resource is "text/html". Abort these steps.
  7. If the bytes with positions pos to pos+2 in s are exactly equal to 0x21, 0x2D, 0x2D respectively (ASCII for "!--"), then:

    1. Increase pos by 3.
    2. If the bytes with positions pos to pos+2 in s are exactly equal to 0x2D, 0x2D, 0x3E respectively (ASCII for "-->"), then increase pos by 3 and jump back to the previous step (the step labeled loop start) in the overall algorithm in this section.
    3. Otherwise, increase pos by 1.
    4. Return to step 2 in these substeps.
  8. If s[pos] is 0x21 (ASCII "!"):

    1. Increase pos by 1.
    2. If s[pos] equal 0x3E, then increase pos by 1 and jump back to the step labeled loop start in the overall algorithm in this section.
    3. Otherwise, return to step 1 in these substeps.
  9. If s[pos] is 0x3F (ASCII "?"):

    1. Increase pos by 1.
    2. If s[pos] and s[pos+1] equal 0x3F and 0x3E respectively, then increase pos by 1 and jump back to the step labeled loop start in the overall algorithm in this section.
    3. Otherwise, return to step 1 in these substeps.
  10. Otherwise, if the bytes in s starting at pos match any of the sequences of bytes in the first column of the following table, then the user agent must follow the steps given in the corresponding cell in the second column of the same row.

    Bytes in Hexadecimal Requirement Comment
    72 73 73 The sniffed type of the resource is "application/rss+xml"; abort these steps The three ASCII characters "rss"
    66 65 65 64 The sniffed type of the resource is "application/atom+xml"; abort these steps The four ASCII characters "feed"
    72 64 66 3A 52 44 46 Continue to the next step in this algorithm The ASCII characters "rdf:RDF"

    If none of the byte sequences above match the bytes in s starting at pos, then the sniffed type of the resource is "text/html". Abort these steps.

  11. If, before the next ">", you find two xmlns* attributes with http://www.w3.org/1999/02/22-rdf-syntax-ns# and http://purl.org/rss/1.0/ as the namespaces, then the sniffed type of the resource is "application/rss+xml", abort these steps. (maybe we only need to check for http://purl.org/rss/1.0/ actually)

  12. Otherwise, the sniffed type of the resource is "text/html".

For efficiency reasons, implementations may wish to implement this algorithm and the algorithm for detecting the character encoding of HTML documents in parallel.

2.8 Character encodings

User agents must at a minimum support the UTF-8 and Windows-1252 encodings, but may support more.

It is not unusual for Web browsers to support dozens if not upwards of a hundred distinct character encodings.

User agents must support the preferred MIME name of every character encoding they support that has a preferred MIME name, and should support all the IANA-registered aliases. [IANACHARSET]

When comparing a string specifying a character encoding with the name or alias of a character encoding to determine if they are equal, user agents must use the Charset Alias Matching rules defined in Unicode Technical Standard #22. [UTS22]

For instance, "GB_2312-80" and "g.b.2312(80)" are considered equivalent names.


When a user agent would otherwise use an encoding given in the first column of the following table to either convert content to Unicode characters or convert Unicode characters to bytes, it must instead use the encoding given in the cell in the second column of the same row. When a byte or sequence of bytes is treated differently due to this encoding aliasing, it is said to have been misinterpreted for compatibility.

Character encoding overrides
Input encoding Replacement encoding References
EUC-KR Windows-949 [EUCKR] [WIN949]
GB2312 GBK [GB2312] [GBK]
GB_2312-80 GBK [RFC1345] [GBK]
ISO-8859-1 Windows-1252 [RFC1345] [WIN1252]
ISO-8859-9 Windows-1254 [RFC1345] [WIN1254]
ISO-8859-11 Windows-874 [ISO885911] [WIN874]
KS_C_5601-1987 Windows-949 [RFC1345] [WIN949]
TIS-620 Windows-874 [TIS620] [WIN874]
US-ASCII Windows-1252 [RFC1345] [WIN1252]
x-x-big5 Big5 [BIG5]

The requirement to treat certain encodings as other encodings according to the table above is a willful violation of the W3C Character Model specification. [CHARMOD]


User agents must not support the CESU-8, UTF-7, BOCU-1 and SCSU encodings. [CESU8] [UTF7] [BOCU1] [SCSU]

Support for encodings based on EBCDIC is not recommended. This encoding is rarely used for publicly-facing Web content.

Support for UTF-32 is not recommended. This encoding is rarely used, and frequently implemented incorrectly.

This specification does not make any attempt to support EBCDIC-based encodings and UTF-32 in its algorithms; support and use of these encodings can thus lead to unexpected behavior in implementations of this specification.

2.9 Common DOM interfaces

2.9.1 Reflecting content attributes in DOM attributes

Some DOM attributes are defined to reflect a particular content attribute. This means that on getting, the DOM attribute returns the current value of the content attribute, and on setting, the DOM attribute changes the value of the content attribute to the given value.

A list of reflecting DOM attributes and their corresponding content attributes is given in the index.

If a reflecting DOM attribute is a DOMString attribute whose content attribute is defined to contain a URL, then on getting, the DOM attribute must resolve the value of the content attribute relative to the element and return the resulting absolute URL if that was successful, or the empty string otherwise; and on setting, must set the content attribute to the specified literal value. If the content attribute is absent, the DOM attribute must return the default value, if the content attribute has one, or else the empty string.

If a reflecting DOM attribute is a DOMString attribute whose content attribute is defined to contain one or more URLs, then on getting, the DOM attribute must split the content attribute on spaces and return the concatenation of resolving each token URL to an absolute URL relative to the element, with a single U+0020 SPACE character between each URL, ignoring any tokens that did not resolve successfully. If the content attribute is absent, the DOM attribute must return the default value, if the content attribute has one, or else the empty string. On setting, the DOM attribute must set the content attribute to the specified literal value.

If a reflecting DOM attribute is a DOMString whose content attribute is an enumerated attribute, and the DOM attribute is limited to only known values, then, on getting, the DOM attribute must return the conforming value associated with the state the attribute is in (in its canonical case), or the empty string if the attribute is in a state that has no associated keyword value; and on setting, if the new value is an ASCII case-insensitive match for one of the keywords given for that attribute, then the content attribute must be set to the conforming value associated with the state that the attribute would be in if set to the given new value, otherwise, if the new value is the empty string, then the content attribute must be removed, otherwise, the setter must raise a SYNTAX_ERR exception.

If a reflecting DOM attribute is a DOMString but doesn't fall into any of the above categories, then the getting and setting must be done in a transparent, case-preserving manner.

If a reflecting DOM attribute is a boolean attribute, then on getting the DOM attribute must return true if the attribute is set, and false if it is absent. On setting, the content attribute must be removed if the DOM attribute is set to false, and must be set to have the same value as its name if the DOM attribute is set to true. (This corresponds to the rules for boolean content attributes.)

If a reflecting DOM attribute is a signed integer type (long) then, on getting, the content attribute must be parsed according to the rules for parsing signed integers, and if that is successful, and the value is in the range of the DOM attribute's type, the resulting value must be returned. If, on the other hand, it fails or returns an out of range value, or if the attribute is absent, then the default value must be returned instead, or 0 if there is no default value. On setting, the given value must be converted to the shortest possible string representing the number as a valid integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is an unsigned integer type (unsigned long) then, on getting, the content attribute must be parsed according to the rules for parsing non-negative integers, and if that is successful, and the value is in the range of the DOM attribute's type, the resulting value must be returned. If, on the other hand, it fails or returns an out of range value, or if the attribute is absent, the default value must be returned instead, or 0 if there is no default value. On setting, the given value must be converted to the shortest possible string representing the number as a valid non-negative integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is an unsigned integer type (unsigned long) that is limited to only positive non-zero numbers, then the behavior is similar to the previous case, but zero is not allowed. On getting, the content attribute must first be parsed according to the rules for parsing non-negative integers, and if that is successful, and the value is in the range of the DOM attribute's type, the resulting value must be returned. If, on the other hand, it fails or returns an out of range value, or if the attribute is absent, the default value must be returned instead, or 1 if there is no default value. On setting, if the value is zero, the user agent must fire an INDEX_SIZE_ERR exception. Otherwise, the given value must be converted to the shortest possible string representing the number as a valid non-negative integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is a floating point number type (float) and it doesn't fall into one of the earlier categories, then, on getting, the content attribute must be parsed according to the rules for parsing floating point number values, and if that is successful, and the value is in the range of the DOM attribute's type, the resulting value must be returned. If, on the other hand, it fails or returns an out of range value, or if the attribute is absent, the default value must be returned instead, or 0.0 if there is no default value. On setting, the given value must be converted to the best representation of the floating point number and then that string must be used as the new content attribute value.

The values ±Infinity and NaN throw an exception on setting, as defined by WebIDL. [WEBIDL]

If a reflecting DOM attribute is of the type DOMTokenList, then on getting it must return a DOMTokenList object whose underlying string is the element's corresponding content attribute. When the DOMTokenList object mutates its underlying string, the content attribute must itself be immediately mutated. When the attribute is absent, then the string represented by the DOMTokenList object is the empty string; when the object mutates this empty string, the user agent must first add the corresponding content attribute, and then mutate that attribute instead. DOMTokenList attributes are always read-only. The same DOMTokenList object must be returned every time for each attribute.

If a reflecting DOM attribute has the type HTMLElement, or an interface that descends from HTMLElement, then, on getting, it must run the following algorithm (stopping at the first point where a value is returned):

  1. If the corresponding content attribute is absent, then the DOM attribute must return null.
  2. Let candidate be the element that the document.getElementById() method would find if it was passed as its argument the current value of the corresponding content attribute.
  3. If candidate is null, or if it is not type-compatible with the DOM attribute, then the DOM attribute must return null.
  4. Otherwise, it must return candidate.

On setting, if the given element has an id attribute, then the content attribute must be set to the value of that id attribute. Otherwise, the DOM attribute must be set to the empty string.

2.9.2 Collections

The HTMLCollection, HTMLFormControlsCollection, and HTMLOptionsCollection interfaces represent various lists of DOM nodes. Collectively, objects implementing these interfaces are called collections.

When a collection is created, a filter and a root are associated with the collection.

For example, when the HTMLCollection object for the document.images attribute is created, it is associated with a filter that selects only img elements, and rooted at the root of the document.

The collection then represents a live view of the subtree rooted at the collection's root, containing only nodes that match the given filter. The view is linear. In the absence of specific requirements to the contrary, the nodes within the collection must be sorted in tree order.

The rows list is not in tree order.

An attribute that returns a collection must return the same object every time it is retrieved.

2.9.2.1 HTMLCollection

The HTMLCollection interface represents a generic collection of elements.

[Callable=namedItem]
interface HTMLCollection {
  readonly attribute unsigned long length;
  [IndexGetter] Element item(in unsigned long index);
  [NameGetter] Element namedItem(in DOMString name);
};
collection . length

Returns the number of elements in the collection.

element = collection . item(index)
collection[index]

Returns the item with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

element = collection . namedItem(name)
collection[name]

Returns the first item with ID or name name from the collection.

Returns null if no element with that ID or name could be found.

Only a, applet, area, embed, form, frame, frameset, iframe, img, and object elements can have a name for the purpose of this method; their name is given by the value of their name attribute.


The object's indices of the supported indexed properties are the numbers in the range zero to one less than the number of nodes represented by the collection. If there are no such elements, then there are no supported indexed properties.

The length attribute must return the number of nodes represented by the collection.

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The names of the supported named properties consist of the values of the name attributes of each a, applet, area, embed, form, frame, frameset, iframe, img, and object element represented by the collection with a name attribute, plus the list of IDs that the elements represented by the collection have.

The namedItem(key) method must return the first node in the collection that matches the following requirements:

If no such elements are found, then the method must return null.

2.9.2.2 HTMLFormControlsCollection

The HTMLFormControlsCollection interface represents a collection of listed elements in form and fieldset elements.

[Callable=namedItem]
interface HTMLFormControlsCollection {
  readonly attribute unsigned long length;
  [IndexGetter] HTMLElement item(in unsigned long index);
  [NameGetter] Object namedItem(in DOMString name);
};

interface RadioNodeList : NodeList {
          attribute DOMString value;
};
collection . length

Returns the number of elements in the collection.

element = collection . item(index)
collection[index]

Returns the item with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

element = collection . namedItem(name)
radioNodeList = collection . namedItem(name)
collection[name]

Returns the item with ID or name name from the collection.

If there are multiple matching items, then a RadioNodeList object containing all those elements is returned.

Returns null if no element with that ID or name could be found.

radioNodeList . value [ = value ]

Returns the value of the first checked radio button represented by the object.

Can be set, to check the first radio button with the given value represented by the object.


The object's indices of the supported indexed properties are the numbers in the range zero to one less than the number of nodes represented by the collection. If there are no such elements, then there are no supported indexed properties.

The length attribute must return the number of nodes represented by the collection.

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The names of the supported named properties consist of the values of all the id and name attributes of all the elements represented by the collection.

The namedItem(name) method must act according to the following algorithm:

  1. If, at the time the method is called, there is exactly one node in the collection that has either an id attribute or a name attribute equal to name, then return that node and stop the algorithm.
  2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to name, then return null and stop the algorithm.
  3. Otherwise, create a RadioNodeList object representing a live view of the HTMLFormControlsCollection object, further filtered so that the only nodes in the RadioNodeList object are those that have either an id attribute or a name attribute equal to name. The nodes in the RadioNodeList object must be sorted in tree order.
  4. Return that RadioNodeList object.

A members of the RadioNodeList interface inherited from the NodeList interface must behave as they would on a NodeList object.

The value DOM attribute on the RadioNodeList object, on getting, must return the value returned by running the following steps:

  1. Let element be the first element in tree order represented by the RadioNodeList object that is an input element whose type attribute is in the Radio Button state and whose checkedness is true. Otherwise, let it be null.

  2. If element is null, or if it is an element with no value attribute, return the empty string.

  3. Otherwise, return the value of element's value attribute.

On setting, the value DOM attribute must run the following steps:

  1. Let element be the first element in tree order represented by the RadioNodeList object that is an input element whose type attribute is in the Radio Button state and whose value content attribute is present and equal to the new value, if any. Otherwise, let it be null.

  2. If element is not null, then set its checkedness to true.

2.9.2.3 HTMLOptionsCollection

The HTMLOptionsCollection interface represents a list of option elements. It is always rooted on a select element and has attributes and methods that manipulate that element's descendants.

[Callable=namedItem]
interface HTMLOptionsCollection {
           attribute unsigned long length;
  [IndexGetter] HTMLOptionElement item(in unsigned long index);
  [NameGetter] Object namedItem(in DOMString name);
  void add(in HTMLElement element, [Optional] in HTMLElement before);
  void add(in HTMLElement element, in long before);
  void remove(in long index);
};
collection . length [ = value ]

Returns the number of elements in the collection.

When set to a smaller number, truncates the number of option elements in the corresponding container.

When set to a greater number, adds new blank option elements to that container.

element = collection . item(index)
collection[index]

Returns the item with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

element = collection . namedItem(name)
collection[name]

Returns the item with ID or name name from the collection.

If there are multiple matching items, then a NodeList object containing all those elements is returned.

Returns null if no element with that ID could be found.

collection . add(element [, before ] )

Inserts element before the node given by before.

The before argument can be a number, in which case element is inserted before the item with that number, or an element from the collection, in which case element is inserted before that element.

If before is omitted, null, or a number out of range, then element will be added at the end of the list.

This method will throw a HIERARCHY_REQUEST_ERR exception if element is an ancestor of the element into which it is to be inserted. If element is not an option or optgroup element, then the method does nothing.

The object's indices of the supported indexed properties are the numbers in the range zero to one less than the number of nodes represented by the collection. If there are no such elements, then there are no supported indexed properties.

On getting, the length attribute must return the number of nodes represented by the collection.

On setting, the behavior depends on whether the new value is equal to, greater than, or less than the number of nodes represented by the collection at that time. If the number is the same, then setting the attribute must do nothing. If the new value is greater, then n new option elements with no attributes and no child nodes must be appended to the select element on which the HTMLOptionsCollection is rooted, where n is the difference between the two numbers (new value minus old value). If the new value is lower, then the last n nodes in the collection must be removed from their parent nodes, where n is the difference between the two numbers (old value minus new value).

Setting length never removes or adds any optgroup elements, and never adds new children to existing optgroup elements (though it can remove children from them).

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The names of the supported named properties consist of the values of all the id and name attributes of all the elements represented by the collection.

The namedItem(name) method must act according to the following algorithm:

  1. If, at the time the method is called, there is exactly one node in the collection that has either an id attribute or a name attribute equal to name, then return that node and stop the algorithm.
  2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to name, then return null and stop the algorithm.
  3. Otherwise, create a NodeList object representing a live view of the HTMLOptionsCollection object, further filtered so that the only nodes in the NodeList object are those that have either an id attribute or a name attribute equal to name. The nodes in the NodeList object must be sorted in tree order.
  4. Return that NodeList object.

The add(element, before) method must act according to the following algorithm:

  1. If element is not an option or optgroup element, then return and abort these steps.

  2. If element is an ancestor of the select element element on which the HTMLOptionsCollection is rooted, then throw a HIERARCHY_REQUEST_ERR exception.

  3. If before is an element, but that element isn't a descendant of the select element element on which the HTMLOptionsCollection is rooted, then throw a NOT_FOUND_ERR exception.

  4. If element and before are the same element, then return and abort these steps.

  5. If before is a node, then let reference be that node. Otherwise, if before is an integer, and there is a beforeth node in the collection, let reference be that node. Otherwise, let reference be null.

  6. If reference is not null, let parent be the parent node of reference. Otherwise, let parent be the select element element on which the HTMLOptionsCollection is rooted.

  7. Act as if the DOM Core insertBefore() method was invoked on the parent node, with element as the first argument and reference as the second argument.

The remove(index) method must act according to the following algorithm:

  1. If the number of nodes represented by the collection is zero, abort these steps.

  2. If index is not a number greater than or equal to 0 and less than the number of nodes represented by the collection, let element be the first element in the collection. Otherwise, let element be the indexth element in the collection.

  3. Remove element from its parent node.

2.9.3 DOMTokenList

The DOMTokenList interface represents an interface to an underlying string that consists of an unordered set of unique space-separated tokens.

[Stringifies] interface DOMTokenList {
  readonly attribute unsigned long length;
  [IndexGetter] DOMString item(in unsigned long index);
  boolean has(in DOMString token);
  void add(in DOMString token);
  void remove(in DOMString token);
  boolean toggle(in DOMString token);
};
tokenlist . length

Returns the number of tokens in the string.

element = tokenlist . item(index)
tokenlist[index]

Returns the token with index index. The tokens are sorted alphabetically.

Returns null if index is out of range.

has-p = tokenlist . has(token)

Returns true if the token is present; false otherwise.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

tokenlist . add(token)

Adds token, unless it is already present.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

tokenlist . remove(token)

Removes token if it is present.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

has-p = tokenlist . toggle(token)

Adds token if it is not present, or removes it if it is.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

The length attribute must return the number of unique tokens that result from splitting the underlying string on spaces. This is the length.

The object's indices of the supported indexed properties are the numbers in the range zero to length-1, unless the length is zero, in which case there are no supported indexed properties.

The item(index) method must split the underlying string on spaces, sort the resulting list of tokens by Unicode code point, remove exact duplicates, and then return the indexth item in this list. If index is equal to or greater than the number of tokens, then the method must return null.

The has(token) method must run the following algorithm:

  1. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the token indicated by token is one of the tokens in the object's underlying string then return true and stop this algorithm.
  4. Otherwise, return false.

The add(token) method must run the following algorithm:

  1. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the given token is already one of the tokens in the DOMTokenList object's underlying string then stop the algorithm.
  4. Otherwise, if the DOMTokenList object's underlying string is not the empty string and the last character of that string is not a space character, then append a U+0020 SPACE character to the end of that string.
  5. Append the value of token to the end of the DOMTokenList object's underlying string.

The remove(token) method must run the following algorithm:

  1. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, remove the given token from the underlying string.

The toggle(token) method must run the following algorithm:

  1. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the given token is already one of the tokens in the DOMTokenList object's underlying string then remove the given token from the underlying string, and stop the algorithm, returning false.
  4. Otherwise, if the DOMTokenList object's underlying string is not the empty string and the last character of that string is not a space character, then append a U+0020 SPACE character to the end of that string.
  5. Append the value of token to the end of the DOMTokenList object's underlying string.
  6. Return true.

Objects implementing the DOMTokenList interface must stringify to the object's underlying string representation.

2.9.4 Safe passing of structured data

When a user agent is required to obtain a structured clone of an object, it must run the following algorithm, which either returns a separate object, or throws an exception.

  1. Let input be the object being cloned.

  2. Let memory be a list of objects, initially empty. (This is used to catch cycles.)

  3. Let output be the object resulting from calling the internal structured cloning algorithm with input and memory.

  4. Return output.

The internal structured cloning algorithm is always called with two arguments, input and memory, and its behavior depends on the type of input, as follows:

If input is the undefined value

Return the undefined value.

If input is the null value

Return the null value.

If input is the false value

Return the false value.

If input is the true value

Return the true value.

If input is a Number object

Return a newly constructed Number object with the same value as input.

If input is a String object

Return a newly constructed String object with the same value as input.

If input is a Date object

Return a newly constructed Date object with the same value as input.

If input is a RegExp object

Return a newly constructed RegExp object with the same pattern and flags as input.

The value of the lastIndex property is not copied.

If input is a ImageData object

Return a newly constructed ImageData object with the same width and height as input, and with a newly constructed CanvasPixelArray for its data attribute, with the same length and pixel values as the input's.

If input is a host object (e.g. a DOM node)

Return the null value.

If input is an Array object
If input is an Object object
  1. If input is in memory, then throw a NOT_SUPPORTED_ERR exception and abort the overall structured clone algorithm.

  2. Otherwise, let new memory be a list consisting of the items in memory with the addition of input.

  3. Create a new object, output, of the same type as input: either an Array or an Object.

  4. For each enumerable property in input, add a corresponding property to output having the same name, and having a value created from invoking the internal structured cloning algorithm recursively with the value of the property as the "input" argument and new memory as the "memory" argument. The order of the properties in the input and output objects must be the same.

    This does not walk the prototype chain.

  5. Return output.

If input is another native object type (e.g. Error)

Return the null value.

2.9.5 DOMStringMap

The DOMStringMap interface represents a set of name-value pairs. It exposes these using the scripting language's native mechanisms for property access.

When a DOMStringMap object is instantiated, it is associated with three algorithms, one for getting the list of name-value pairs, one for setting names to certain values, and one for deleting names.

[NameCreator, NameDeleter, NameGetter, NameSetter]
interface DOMStringMap {};

The names of the supported named properties on a DOMStringMap object at any instant are the names of each pair returned from the algorithm for getting the list of name-value pairs at that instant.

When a DOMStringMap object is indexed to retrieve a named property name, the value returned must be the value component of the name-value pair whose name component is name in the list returned by the algorithm for getting the list of name-value pairs.

When a DOMStringMap object is indexed to create or modify a named property name with value value, the algorithm for setting names to certain values must be run, passing name as the name and the result of converting value to a DOMString as the value.

When a DOMStringMap object is indexed to delete a named property named name, the algorithm for deleting names must be run, passing name as the name.

The DOMStringMap interface definition here is only intended for JavaScript environments. Other language bindings will need to define how DOMStringMap is to be implemented for those languages.

The dataset attribute on elements exposes the data-* attributes on the element.

Given the following fragment and elements with similar constructions:

<img class="tower" id="tower5" data-x="12" data-y="5"
     data-ai="robotarget" data-hp="46" data-ability="flames"
     src="towers/rocket.png alt="Rocket Tower">

...one could imagine a function splashDamage() that takes some arguments, the first of which is the element to process:

function splashDamage(node, x, y, damage) {
  if (node.classList.has('tower') && // checking the 'class' attribute
      node.dataset.x == x && // reading the 'data-x' attribute
      node.dataset.y == y) { // reading the 'data-y' attribute
    var hp = parseInt(node.dataset.hp); // reading the 'data-hp' attribute
    hp = hp - damage;
    if (hp < 0) {
      hp = 0;
      node.dataset.ai = 'dead'; // setting the 'data-ai' attribute
      delete node.dataset.ability; // removing the 'data-ability' attribute
    }
    node.dataset.hp = hp; // setting the 'data-hp' attribute
  }
}

2.9.6 DOM feature strings

DOM3 Core defines mechanisms for checking for interface support, and for obtaining implementations of interfaces, using feature strings. [DOM3CORE]

A DOM application can use the hasFeature(feature, version) method of the DOMImplementation interface with parameter values "HTML" and "5.0" (respectively) to determine whether or not this module is supported by the implementation. In addition to the feature string "HTML", the feature string "XHTML" (with version string "5.0") can be used to check if the implementation supports XHTML. User agents should respond with a true value when the hasFeature method is queried with these values. Authors are cautioned, however, that UAs returning true might not be perfectly compliant, and that UAs returning false might well have support for features in this specification; in general, therefore, use of this method is discouraged.

The values "HTML" and "XHTML" (both with version "5.0") should also be supported in the context of the getFeature() and isSupported() methods, as defined by DOM3 Core.

The interfaces defined in this specification are not always supersets of the interfaces defined in DOM2 HTML; some features that were formerly deprecated, poorly supported, rarely used or considered unnecessary have been removed. Therefore it is not guaranteed that an implementation that supports "HTML" "5.0" also supports "HTML" "2.0".

2.9.7 Exceptions

The following DOMException codes are defined in DOM Core. [DOMCORE]

  1. INDEX_SIZE_ERR
  2. DOMSTRING_SIZE_ERR
  3. HIERARCHY_REQUEST_ERR
  4. WRONG_DOCUMENT_ERR
  5. INVALID_CHARACTER_ERR
  6. NO_DATA_ALLOWED_ERR
  7. NO_MODIFICATION_ALLOWED_ERR
  8. NOT_FOUND_ERR
  9. NOT_SUPPORTED_ERR
  10. INUSE_ATTRIBUTE_ERR
  11. INVALID_STATE_ERR
  12. SYNTAX_ERR
  13. INVALID_MODIFICATION_ERR
  14. NAMESPACE_ERR
  15. INVALID_ACCESS_ERR
  16. VALIDATION_ERR
  17. TYPE_MISMATCH_ERR
  18. SECURITY_ERR
  19. NETWORK_ERR
  20. ABORT_ERR
  21. URL_MISMATCH_ERR
  22. QUOTA_EXCEEDED_ERR
  23. DATAGRID_MODEL_ERR
  24. PARSE_ERR
  25. SERIALISE_ERR

2.9.8 Garbage collection

There is an implied strong reference from any DOM attribute that returns a pre-existing object to that object.

For example, the document.location attribute means that there is a strong reference from a Document object to its Location object. Similarly, there is always a strong reference from a Document to any descendant nodes, and from any node to its owner Document.

3 Semantics and structure of HTML documents

3.1 Introduction

This section is non-normative.

An introduction to marking up a document.

3.2 Documents

Every XML and HTML document in an HTML UA is represented by a Document object. [DOM3CORE]

The document's address is an absolute URL that is set when the Document is created. The document's current address is an absolute URL that can change during the lifetime of the Document, for example when the user navigates to a fragment identifier on the page. The document's current address must be set to the document's address when the Document is created.

For purposes of generating the address of the resource from which Request-URIs are obtained as required by HTTP for the Referer (sic) header, the user agent must use the document's current address. [HTTP]

When a Document is created by a script using the createDocument() API, the document's address is the same as the document's address of the active document of the script's browsing context.

Document objects are assumed to be XML documents unless they are flagged as being HTML documents when they are created. Whether a document is an HTML document or an XML document affects the behavior of certain APIs, as well as a few CSS rendering rules. [CSS21]

A Document object created by the createDocument() API on the DOMImplementation object is initially an XML document, but can be made into an HTML document by calling document.open() on it.

3.2.1 Documents in the DOM

All Document objects (in user agents implementing this specification) must also implement the HTMLDocument interface, available using binding-specific methods. (This is the case whether or not the document in question is an HTML document or indeed whether it contains any HTML elements at all.) Document objects must also implement the document-level interface of any other namespaces found in the document that the UA supports.

For example, if an HTML implementation also supports SVG, then the Document object implements both HTMLDocument and SVGDocument.

Because the HTMLDocument interface is now obtained using binding-specific casting methods instead of simply being the primary interface of the document object, it is no longer defined as inheriting from Document.

[NameGetter=OverrideBuiltins, ImplementedOn=Document]
interface HTMLDocument {
  // resource metadata management
  [PutForwards=href] readonly attribute Location location;
  readonly attribute DOMString URL;
           attribute DOMString domain;
  readonly attribute DOMString referrer;
           attribute DOMString cookie;
  readonly attribute DOMString lastModified;
  readonly attribute DOMString compatMode;
           attribute DOMString charset;
  readonly attribute DOMString characterSet;
  readonly attribute DOMString defaultCharset;
  readonly attribute DOMString readyState;

  // DOM tree accessors
           attribute DOMString title;
           attribute DOMString dir;
           attribute HTMLElement body;
  readonly attribute HTMLCollection images;
  readonly attribute HTMLCollection embeds;
  readonly attribute HTMLCollection plugins;
  readonly attribute HTMLCollection links;
  readonly attribute HTMLCollection forms;
  readonly attribute HTMLCollection anchors;
  readonly attribute HTMLCollection scripts;
  NodeList getElementsByName(in DOMString elementName);
  NodeList getElementsByClassName(in DOMString classNames);

  // dynamic markup insertion
           attribute DOMString innerHTML;
  HTMLDocument open([Optional] in DOMString type, [Optional] in DOMString replace);
  WindowProxy open(in DOMString url, in DOMString name, in DOMString features, [Optional] in boolean replace);
  void close();
  void write([Variadic] in DOMString text);
  void writeln([Variadic] in DOMString text);

  // user interaction
  Selection getSelection();
  readonly attribute Element activeElement;
  boolean hasFocus();
           attribute DOMString designMode;
  boolean execCommand(in DOMString commandId);
  boolean execCommand(in DOMString commandId, in boolean showUI);
  boolean execCommand(in DOMString commandId, in boolean showUI, in DOMString value);
  boolean queryCommandEnabled(in DOMString commandId);
  boolean queryCommandIndeterm(in DOMString commandId);
  boolean queryCommandState(in DOMString commandId);
  boolean queryCommandSupported(in DOMString commandId);
  DOMString queryCommandValue(in DOMString commandId);
  readonly attribute HTMLCollection commands;

  // event handler DOM attributes
           attribute Function onabort;
           attribute Function onblur;
           attribute Function oncanplay;
           attribute Function oncanplaythrough;
           attribute Function onchange;
           attribute Function onclick;
           attribute Function oncontextmenu;
           attribute Function ondataunavailable;
           attribute Function ondblclick;
           attribute Function ondrag;
           attribute Function ondragend;
           attribute Function ondragenter;
           attribute Function ondragleave;
           attribute Function ondragover;
           attribute Function ondragstart;
           attribute Function ondrop;
           attribute Function ondurationchange;
           attribute Function onemptied;
           attribute Function onended;
           attribute Function onerror;
           attribute Function onfocus;
           attribute Function onformchange;
           attribute Function onforminput;
           attribute Function oninput;
           attribute Function oninvalid;
           attribute Function onkeydown;
           attribute Function onkeypress;
           attribute Function onkeyup;
           attribute Function onload;
           attribute Function onloadeddata;
           attribute Function onloadedmetadata;
           attribute Function onloadstart;
           attribute Function onmousedown;
           attribute Function onmousemove;
           attribute Function onmouseout;
           attribute Function onmouseover;
           attribute Function onmouseup;
           attribute Function onmousewheel;
           attribute Function onpause;
           attribute Function onplay;
           attribute Function onplaying;
           attribute Function onprogress;
           attribute Function onratechange;
           attribute Function onreadystatechange;
           attribute Function onscroll;
           attribute Function onseeked;
           attribute Function onseeking;
           attribute Function onselect;
           attribute Function onshow;
           attribute Function onstalled;
           attribute Function onsubmit;
           attribute Function onsuspend;
           attribute Function ontimeupdate;
           attribute Function onvolumechange;
           attribute Function onwaiting;
};

Since the HTMLDocument interface holds methods and attributes related to a number of disparate features, the members of this interface are described in various different sections.

3.2.2 Security

User agents must raise a SECURITY_ERR exception whenever any of the members of an HTMLDocument object are accessed by scripts whose effective script origin is not the same as the Document's effective script origin.

3.2.3 Resource metadata management

document . URL

Returns the document's address.

document . referrer

Returns the address of the Document from which the user navigated to this one, unless it was blocked or there was no such document, in which case it returns the empty string.

The noreferrer link type can be used to block the referrer.

The URL attribute must return the document's address.

The referrer attribute must return either the current address of the active document of the source browsing context at the time the navigation was started (that is, the page which navigated the browsing context to the current document), or the empty string if there is no such originating page, or if the UA has been configured not to report referrers in this case, or if the navigation was initiated for a hyperlink with a noreferrer keyword.

In the case of HTTP, the referrer DOM attribute will match the Referer (sic) header that was sent when fetching the current page.

Typically user agents are configured to not report referrers in the case where the referrer uses an encrypted protocol and the current page does not (e.g. when navigating from an https: page to an http: page).


document . cookie [ = value ]

Returns the HTTP cookies that apply to the Document. If there are no cookies or cookies can't be applied to this resource, the empty string will be returned.

Can be set, to add a new cookie to the element's set of HTTP cookies.

If the Document has no browsing context an INVALID_STATE_ERR exception will be thrown. If the contents are sandboxed into a unique origin, a SECURITY_ERR exception will be thrown.

The cookie attribute represents the cookies of the resource.

On getting, if the document is not associated with a browsing context then the user agent must raise an INVALID_STATE_ERR exception. Otherwise, if the sandboxed origin browsing context flag was set on the browsing context of the Document when the Document was created, the user agent must raise a SECURITY_ERR exception. Otherwise, if the document's address does not use a server-based naming authority, it must return the empty string. Otherwise, it must first obtain the storage mutex and then return the same string as the value of the Cookie HTTP header it would include if fetching the resource indicated by the document's address over HTTP, as per RFC 2109 section 4.3.4 or later specifications, excluding HTTP-only cookies. [RFC2109] [RFC2965]

On setting, if the document is not associated with a browsing context then the user agent must raise an INVALID_STATE_ERR exception. Otherwise, if the sandboxed origin browsing context flag was set on the browsing context of the Document when the Document was created, the user agent must raise a SECURITY_ERR exception. Otherwise, if the document's address does not use a server-based naming authority, it must do nothing. Otherwise, the user agent must obtain the storage mutex and then act as it would when processing cookies if it had just attempted to fetch the document's address over HTTP, and had received a response with a Set-Cookie header whose value was the specified value, as per RFC 2109 sections 4.3.1, 4.3.2, and 4.3.3 or later specifications, but without overwriting the values of HTTP-only cookies. [RFC2109] [RFC2965]

This specification does not define what makes an HTTP-only cookie, and at the time of publication the editor is not aware of any reference for HTTP-only cookies. They are a feature supported by some Web browsers wherein an "httponly" parameter added to the cookie string causes the cookie to be hidden from script.

Since the cookie attribute is accessible across frames, the path restrictions on cookies are only a tool to help manage which cookies are sent to which parts of the site, and are not in any way a security feature.


document . lastModified

Returns the date of the last modification to the document, as reported by the server, in the form "MM/DD/YYYY hh:mm:ss".

If the last modification date is not known, the current time is returned instead.

The lastModified attribute, on getting, must return the date and time of the Document's source file's last modification, in the user's local time zone, in the following format:

  1. The month component of the date.
  2. A U+002F SOLIDUS character ('/').
  3. The day component of the date.
  4. A U+002F SOLIDUS character ('/').
  5. The year component of the date.
  6. A U+0020 SPACE character.
  7. The hours component of the time.
  8. A U+003A COLON character (':').
  9. The minutes component of the time.
  10. A U+003A COLON character (':').
  11. The seconds component of the time.

All the numeric components above, other than the year, must be given as two digits in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE representing the number in base ten, zero-padded if necessary. The year must be given as four or more digits in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE representing the number in base ten, zero-padded if necessary.

The Document's source file's last modification date and time must be derived from relevant features of the networking protocols used, e.g. from the value of the HTTP Last-Modified header of the document, or from metadata in the file system for local files. If the last modification date and time are not known, the attribute must return the current date and time in the above format.


document . compatMode

In a conforming document, returns the string "CSS1Compat". (In quirks mode documents, returns the string "BackCompat", but a conforming document can never trigger quirks mode.)

A Document is always set to one of three modes: no quirks mode, the default; quirks mode, used typically for legacy documents; and limited quirks mode, also known as "almost standards" mode. The mode is only ever changed from the default by the HTML parser, based on the presence, absence, or value of the DOCTYPE string.

The compatMode DOM attribute must return the literal string "CSS1Compat" unless the document has been set to quirks mode by the HTML parser, in which case it must instead return the literal string "BackCompat".

As far as parsing goes, the quirks I know of are:


document . charset [ = value ]

Returns the document's character encoding.

Can be set, to dynamically change the document's character encoding.

New values that are not IANA-registered aliases are ignored.

document . characterSet

Returns the document's character encoding.

document . defaultCharset

Returns what might be the user agent's default character encoding.

Documents have an associated character encoding. When a Document object is created, the document's character encoding must be initialized to UTF-16. Various algorithms during page loading affect this value, as does the charset setter. [IANACHARSET]

The charset DOM attribute must, on getting, return the preferred MIME name of the document's character encoding. On setting, if the new value is an IANA-registered alias for a character encoding, the document's character encoding must be set to that character encoding. (Otherwise, nothing happens.)

The characterSet DOM attribute must, on getting, return the preferred MIME name of the document's character encoding.

The defaultCharset DOM attribute must, on getting, return the preferred MIME name of a character encoding, possibly the user's default encoding, or an encoding associated with the user's current geographical location, or any arbitrary encoding name.


document . readyState

Returns "loading" while the Document is loading, and "complete" once it has loaded.

The readystatechange event fires on the Document object when this value changes.

Each document has a current document readiness. When a Document object is created, it must have its current document readiness set to the string "loading" if the document is associated with an HTML parser or an XML parser, or to the string "complete" otherwise. Various algorithms during page loading affect this value. When the value is set, the user agent must fire a simple event called readystatechange at the Document object.

The readyState DOM attribute must, on getting, return the current document readiness.

3.2.4 DOM tree accessors

The html element of a document is the document's root element, if there is one and it's an html element, or null otherwise.

The head element of a document is the first head element that is a child of the html element, if there is one, or null otherwise.


document . title [ = value ]

Returns the document's title, as given by the title element.

Can be set, to update the document's title. If there is no head element, the new value is ignored.

In SVG documents, the SVGDocument interface's title attribute takes precedence.

The title element of a document is the first title element in the document (in tree order), if there is one, or null otherwise.

The title attribute must, on getting, run the following algorithm:

  1. If the root element is an svg element in the "http://www.w3.org/2000/svg" namespace, and the user agent supports SVG, then the getter must return the value that would have been returned by the DOM attribute of the same name on the SVGDocument interface. [SVG]

  2. Otherwise, it must return a concatenation of the data of all the child text nodes of the title element, in tree order, or the empty string if the title element is null.

On setting, the following algorithm must be run. Mutation events must be fired as appropriate.

  1. If the root element is an svg element in the "http://www.w3.org/2000/svg" namespace, and the user agent supports SVG, then the setter must defer to the setter for the DOM attribute of the same name on the SVGDocument interface (if it is readonly, then this will raise an exception). Stop the algorithm here. [SVG]

  2. If the title element is null and the head element is null, then the attribute must do nothing. Stop the algorithm here.
  3. If the title element is null, then a new title element must be created and appended to the head element.
  4. The children of the title element (if any) must all be removed.
  5. A single Text node whose data is the new value being assigned must be appended to the title element.

The title attribute on the HTMLDocument interface should shadow the attribute of the same name on the SVGDocument interface when the user agent supports both HTML and SVG. [SVG]


document . body [ = value ]

Returns the body element.

Can be set, to replace the body element.

If the new value is not a body or frameset element, this will throw a HIERARCHY_REQUEST_ERR exception.

The body element of a document is the first child of the html element that is either a body element or a frameset element. If there is no such element, it is null. If the body element is null, then when the specification requires that events be fired at "the body element", they must instead be fired at the Document object.

The body attribute, on getting, must return the body element of the document (either a body element, a frameset element, or null). On setting, the following algorithm must be run:

  1. If the new value is not a body or frameset element, then raise a HIERARCHY_REQUEST_ERR exception and abort these steps.
  2. Otherwise, if the new value is the same as the body element, do nothing. Abort these steps.
  3. Otherwise, if the body element is not null, then replace that element with the new value in the DOM, as if the root element's replaceChild() method had been called with the new value and the incumbent body element as its two arguments respectively, then abort these steps.
  4. Otherwise, the the body element is null. Append the new value to the root element.

document . images

Returns an HTMLCollection of the img elements in the Document.

document . embeds
document . plugins

Return an HTMLCollection of the embed elements in the Document.

document . links

Returns an HTMLCollection of the a and area elements in the Document that have href attributes.

document . forms

Return an HTMLCollection of the form elements in the Document.

document . scripts

Return an HTMLCollection of the script elements in the Document.

The images attribute must return an HTMLCollection rooted at the Document node, whose filter matches only img elements.

The embeds attribute must return an HTMLCollection rooted at the Document node, whose filter matches only embed elements.

The plugins attribute must return the same object as that returned by the embeds attribute.

The links attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with href attributes and area elements with href attributes.

The forms attribute must return an HTMLCollection rooted at the Document node, whose filter matches only form elements.

The anchors attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with name attributes.

The scripts attribute must return an HTMLCollection rooted at the Document node, whose filter matches only script elements.


collection = document . getElementsByName(name)

Returns a NodeList of a, applet, button, form, frame, frameset, iframe, img, input, map, meta, object, select, and textarea elements in the Document that have a name attribute with the value name.

collection = document . getElementsByClassName(classes)
collection = element . getElementsByClassName(classes)

Returns a NodeList of the elements in the object on which the method was invoked (a Document or an Element) that have all the classes given by classes.

The classes argument is interpreted as a space-separated list of classes.

The getElementsByName(name) method takes a string name, and must return a live NodeList containing all the a, applet, button, form, frame, frameset, iframe, img, input, map, meta, object, select, and textarea elements in that document that have a name attribute whose value is equal to the name argument (in a case-sensitive manner), in tree order.

The getElementsByClassName(classNames) method takes a string that contains an unordered set of unique space-separated tokens representing classes. When called, the method must return a live NodeList object containing all the elements in the document, in tree order, that have all the classes specified in that argument, having obtained the classes by splitting a string on spaces. If there are no tokens specified in the argument, then the method must return an empty NodeList. If the document is in quirks mode, then the comparisons for the classes must be done in an ASCII case-insensitive manner, otherwise, the comparisons must be done in a case-sensitive manner.

The getElementsByClassName(classNames) method on the HTMLElement interface must return a live NodeList with the nodes that the HTMLDocument getElementsByClassName() method would return when passed the same argument(s), excluding any elements that are not descendants of the HTMLElement object on which the method was invoked.

HTML, SVG, and MathML elements define which classes they are in by having an attribute in the per-element partition with the name class containing a space-separated list of classes to which the element belongs. Other specifications may also allow elements in their namespaces to be labeled as being in specific classes.

Given the following XHTML fragment:

<div id="example">
 <p id="p1" class="aaa bbb"/>
 <p id="p2" class="aaa ccc"/>
 <p id="p3" class="bbb ccc"/>
</div>

A call to document.getElementById('example').getElementsByClassName('aaa') would return a NodeList with the two paragraphs p1 and p2 in it.

A call to getElementsByClassName('ccc bbb') would only return one node, however, namely p3. A call to document.getElementById('example').getElementsByClassName('bbb  ccc ') would return the same thing.

A call to getElementsByClassName('aaa,bbb') would return no nodes; none of the elements above are in the "aaa,bbb" class.


The HTMLDocument interface supports named properties. The names of the supported named properties at any moment consist of the values of the name content attributes of all the applet, embed, form, iframe, img, and fallback-free object elements in the Document that have name content attributes, and the values of the id content attributes of all the applet and fallback-free object elements in the Document that have id content attributes, and the values of the id content attributes of all the img elements in the Document that have both name content attributes and id content attributes.

When the HTMLDocument object is indexed for property retrieval using a name name, then the user agent must return the value obtained using the following steps:

  1. Let elements be the list of named elements with the name name in the Document.

    There will be at least one such element, by definition.

  2. If elements has only one element, and that element is an iframe element, then return the WindowProxy object of the nested browsing context represented by that iframe element, and abort these steps.

  3. Otherwise, if elements has only one element, return that element and abort these steps.

  4. Otherwise return an HTMLCollection rooted at the Document node, whose filter matches only named elements with the name name.

Named elements with the name name, for the purposes of the above algorithm, are those that are either:

An object element is said to be fallback-free if it has no element descendants other than param elements, and no text node descendants that are not inter-element whitespace.


The dir attribute on the HTMLDocument interface is defined along with the dir content attribute.

3.3 Elements

3.3.1 Semantics

Elements, attributes, and attribute values in HTML are defined (by this specification) to have certain meanings (semantics). For example, the ol element represents an ordered list, and the lang attribute represents the language of the content.

Authors must not use elements, attributes, and attribute values for purposes other than their appropriate intended semantic purpose.

For example, the following document is non-conforming, despite being syntactically correct:

<!DOCTYPE html>
<html lang="en-GB">
 <head> <title> Demonstration </title> </head>
 <body>
  <table>
   <tr> <td> My favourite animal is the cat. </td> </tr>
   <tr>
    <td>
     —<a href="http://example.org/~ernest/"><cite>Ernest</cite></a>,
     in an essay from 1992
    </td>
   </tr>
  </table>
 </body>
</html>

...because the data placed in the cells is clearly not tabular data (and the cite element mis-used). A corrected version of this document might be:

<!DOCTYPE html>
<html lang="en-GB">
 <head> <title> Demonstration </title> </head>
 <body>
  <blockquote>
   <p> My favourite animal is the cat. </p>
  </blockquote>
  <p>
   —<a href="http://example.org/~ernest/">Ernest</a>,
   in an essay from 1992
  </p>
 </body>
</html>

This next document fragment, intended to represent the heading of a corporate site, is similarly non-conforming because the second line is not intended to be a heading of a subsection, but merely a subheading or subtitle (a subordinate heading for the same section).

<body>
 <h1>ABC Company</h1>
 <h2>Leading the way in widget design since 1432</h2>
 ...

The hgroup element should be used in these kinds of situations:

<body>
 <hgroup>
  <h1>ABC Company</h1>
  <h2>Leading the way in widget design since 1432</h2>
 </hgroup>
 ...

Through scripting and using other mechanisms, the values of attributes, text, and indeed the entire structure of the document may change dynamically while a user agent is processing it. The semantics of a document at an instant in time are those represented by the state of the document at that instant in time, and the semantics of a document can therefore change over time. User agents must update their presentation of the document as this occurs.

HTML has a progress element that describes a progress bar. If its "value" attribute is dynamically updated by a script, the UA would update the rendering to show the progress changing.

3.3.2 Elements in the DOM

The nodes representing HTML elements in the DOM must implement, and expose to scripts, the interfaces listed for them in the relevant sections of this specification. This includes HTML elements in XML documents, even when those documents are in another context (e.g. inside an XSLT transform).

Elements in the DOM represent things; that is, they have intrinsic meaning, also known as semantics.

For example, an ol element represents an ordered list.

The basic interface, from which all the HTML elements' interfaces inherit, and which must be used by elements that have no additional requirements, is the HTMLElement interface.

interface HTMLElement : Element {
  // DOM tree accessors
  NodeList getElementsByClassName(in DOMString classNames);

  // dynamic markup insertion
           attribute DOMString innerHTML;
           attribute DOMString outerHTML;
  void insertAdjacentHTML(in DOMString position, in DOMString text);

  // metadata attributes
           attribute DOMString id;
           attribute DOMString title;
           attribute DOMString lang;
           attribute DOMString dir;
           attribute DOMString className;
  readonly attribute DOMTokenList classList;
  readonly attribute DOMStringMap dataset;

  // user interaction
           attribute boolean hidden;
  void click();
  void scrollIntoView();
  void scrollIntoView(in boolean top);
           attribute long tabIndex;
  void focus();
  void blur();
           attribute boolean draggable;
           attribute DOMString contentEditable;
  readonly attribute boolean isContentEditable;
           attribute HTMLMenuElement contextMenu;
           attribute boolean spellcheck;

  // styling
  readonly attribute CSSStyleDeclaration style;

  // event handler DOM attributes
           attribute Function onabort;
           attribute Function onblur;
           attribute Function oncanplay;
           attribute Function oncanplaythrough;
           attribute Function onchange;
           attribute Function onclick;
           attribute Function oncontextmenu;
           attribute Function ondataunavailable;
           attribute Function ondblclick;
           attribute Function ondrag;
           attribute Function ondragend;
           attribute Function ondragenter;
           attribute Function ondragleave;
           attribute Function ondragover;
           attribute Function ondragstart;
           attribute Function ondrop;
           attribute Function ondurationchange;
           attribute Function onemptied;
           attribute Function onended;
           attribute Function onerror;
           attribute Function onfocus;
           attribute Function onformchange;
           attribute Function onforminput;
           attribute Function oninput;
           attribute Function oninvalid;
           attribute Function onkeydown;
           attribute Function onkeypress;
           attribute Function onkeyup;
           attribute Function onload;
           attribute Function onloadeddata;
           attribute Function onloadedmetadata;
           attribute Function onloadstart;
           attribute Function onmousedown;
           attribute Function onmousemove;
           attribute Function onmouseout;
           attribute Function onmouseover;
           attribute Function onmouseup;
           attribute Function onmousewheel;
           attribute Function onpause;
           attribute Function onplay;
           attribute Function onplaying;
           attribute Function onprogress;
           attribute Function onratechange;
           attribute Function onreadystatechange;
           attribute Function onscroll;
           attribute Function onseeked;
           attribute Function onseeking;
           attribute Function onselect;
           attribute Function onshow;
           attribute Function onstalled;
           attribute Function onsubmit;
           attribute Function onsuspend;
           attribute Function ontimeupdate;
           attribute Function onvolumechange;
           attribute Function onwaiting;
};

The HTMLElement interface holds methods and attributes related to a number of disparate features, and the members of this interface are therefore described in various different sections of this specification.

3.3.3 Global attributes

The following attributes are common to and may be specified on all HTML elements (even those not defined in this specification):

In addition, unless otherwise specified, the following event handler content attributes may be specified on any HTML element:

The attributes marked with an asterisk cannot be specified on body elements as those elements expose event handler attributes of the Window object with the same names.


Also, custom data attributes (e.g. data-foldername or data-msgid) can be specified on any HTML element, to store custom data specific to the page.

In HTML documents, elements in the HTML namespace may have an xmlns attribute specified, if, and only if, it has the exact value "http://www.w3.org/1999/xhtml". This does not apply to XML documents.

In HTML, the xmlns attribute has absolutely no effect. It is basically a talisman. It is allowed merely to make migration to and from XHTML mildly easier. When parsed by an HTML parser, the attribute ends up in no namespace, not the "http://www.w3.org/2000/xmlns/" namespace like namespace declaration attributes in XML do.

In XML, an xmlns attribute is part of the namespace declaration mechanism, and an element cannot actually have an xmlns attribute in no namespace specified.

3.3.3.1 The id attribute

The id attribute represents its element's unique identifier. The value must be unique in the element's home subtree and must contain at least one character. The value must not contain any space characters.

If the value is not the empty string, user agents must associate the element with the given value (exactly, including any space characters) for the purposes of ID matching within the element's home subtree (e.g. for selectors in CSS or for the getElementById() method in the DOM).

Identifiers are opaque strings. Particular meanings should not be derived from the value of the id attribute.

This specification doesn't preclude an element having multiple IDs, if other mechanisms (e.g. DOM Core methods) can set an element's ID in a way that doesn't conflict with the id attribute.

The id DOM attribute must reflect the id content attribute.

3.3.3.2 The title attribute

The title attribute represents advisory information for the element, such as would be appropriate for a tooltip. On a link, this could be the title or a description of the target resource; on an image, it could be the image credit or a description of the image; on a paragraph, it could be a footnote or commentary on the text; on a citation, it could be further information about the source; and so forth. The value is text.

If this attribute is omitted from an element, then it implies that the title attribute of the nearest ancestor HTML element with a title attribute set is also relevant to this element. Setting the attribute overrides this, explicitly stating that the advisory information of any ancestors is not relevant to this element. Setting the attribute to the empty string indicates that the element has no advisory information.

If the title attribute's value contains U+000A LINE FEED (LF) characters, the content is split into multiple lines. Each U+000A LINE FEED (LF) character represents a line break.

Caution is advised with respect to the use of newlines in title attributes.

For instance, the following snippet actually defines an abbreviation's expansion with a line break in it:

<p>My logs show that there was some interest in <abbr title="Hypertext
Transport Protocol">HTTP</abbr> today.</p>

Some elements, such as link, abbr, and input, define additional semantics for the title attribute beyond the semantics described above.


The title DOM attribute must reflect the title content attribute.

3.3.3.3 The lang and xml:lang attributes

The lang attribute specifies the primary language for the element's contents and for any of the element's attributes that contain text. Its value must be a valid RFC 3066 language code, or the empty string. [RFC3066]

The xml:lang attribute (that is, the lang attribute with the xml prefix in the http://www.w3.org/XML/1998/namespace namespace) is defined in XML. [XML]

If these attributes are omitted from an element, then the language of this element is the same as the language of its parent element, if any. Setting the attribute to the empty string indicates that the primary language is unknown.

The lang attribute may be used on any HTML element.

The xml:lang attribute may be used on HTML elements in XML documents, as well as elements in other namespaces if the relevant specifications allow it (in particular, MathML and SVG allow xml:lang attributes to be specified on their elements). If both the lang attribute and the xml:lang attribute are specified on the same element, they must have exactly the same value when compared in an ASCII case-insensitive manner.

Authors must not use the xml:lang attribute (that is, the lang attribute with the xml prefix in the http://www.w3.org/XML/1998/namespace namespace) in HTML documents. To ease migration to and from XHTML, authors may specify an attribute in no namespace with no prefix and with the localname xml:lang on HTML elements in HTML documents, but such attributes must only be specified if a lang attribute is also specified, and both attributes must have the same value when compared in an ASCII case-insensitive manner.


To determine the language of a node, user agents must look at the nearest ancestor element (including the element itself if the node is an element) that has an xml:lang attribute set or is an HTML element and has a lang attribute set. That attribute specifies the language of the node.

If both the xml:lang attribute and the lang attribute are set on an element, user agents must use the xml:lang attribute, and the lang attribute must be ignored for the purposes of determining the element's language.

If no explicit language is given for the root element, but there is a document-wide default language set, then that is the language of the node.

If there is no document-wide default language, then language information from a higher-level protocol (such as HTTP), if any, must be used as the final fallback language. In the absence of any language information, the default value is unknown (the empty string).

If the resulting value is not a recognized language code, then it must be treated as an unknown language (as if the value was the empty string).


User agents may use the element's language to determine proper processing or rendering (e.g. in the selection of appropriate fonts or pronunciations, or for dictionary selection).


The lang DOM attribute must reflect the lang content attribute.

3.3.3.4 The xml:base attribute (XML only)

The xml:base attribute is defined in XML Base. [XMLBASE]

The xml:base attribute may be used on elements of XML documents. Authors must not use the xml:base attribute in HTML documents.

3.3.3.5 The dir attribute

The dir attribute specifies the element's text directionality. The attribute is an enumerated attribute with the keyword ltr mapping to the state ltr, and the keyword rtl mapping to the state rtl. The attribute has no defaults.

The processing of this attribute is primarily performed by the presentation layer. For example, the rendering section in this specification defines a mapping from this attribute to the CSS 'direction' and 'unicode-bidi' properties, and CSS defines rendering in terms of those properties.

The directionality of an element, which is used in particular by the canvas element's text rendering API, is either 'ltr' or 'rtl'. If the user agent supports CSS and the 'direction' property on this element has a computed value of either 'ltr' or 'rtl', then that is the directionality of the element. Otherwise, if the element is being rendered, then the directionality of the element is the directionality used by the presentation layer, potentially determined from the value of the dir attribute on the element. Otherwise, if the element's dir attribute has the state ltr, the element's directionality is 'ltr' (left-to-right); if the attribute has the state rtl, the element's directionality is 'rtl' (right-to-left); and otherwise, the element's directionality is the same as its parent element, or 'ltr' if there is no parent element.


document . dir [ = value ]

Returns the html element's dir attribute's value, if any.

Can be set, to either "ltr" or "rtl", to replace the html element's dir attribute's value.

If there is no html element, returns the empty string and ignores new values.

The dir DOM attribute on an element must reflect the dir content attribute of that element, limited to only known values.

The dir DOM attribute on HTMLDocument objects must reflect the dir content attribute of the html element, if any, limited to only known values. If there is no such element, then the attribute must return the empty string and do nothing on setting.

Authors are strongly encouraged to use the dir attribute to indicate text direction rather than using CSS, since that way their documents will continue to render correctly even in the absence of CSS (e.g. as interpreted by search engines).

3.3.3.6 The class attribute

Every HTML element may have a class attribute specified.

The attribute, if specified, must have a value that is an unordered set of unique space-separated tokens representing the various classes that the element belongs to.

The classes that an HTML element has assigned to it consists of all the classes returned when the value of the class attribute is split on spaces.

Assigning classes to an element affects class matching in selectors in CSS, the getElementsByClassName() method in the DOM, and other such features.

Authors may use any value in the class attribute, but are encouraged to use the values that describe the nature of the content, rather than values that describe the desired presentation of the content.


The className and classList DOM attributes must both reflect the class content attribute.

3.3.3.7 The style attribute

All elements may have the style content attribute set. If specified, the attribute must contain only a list of zero or more semicolon-separated (;) CSS declarations. [CSS21]

In user agents that support CSS, the attribute's value must be parsed when the attribute is added or has its value changed, with its value treated as the body (the part inside the curly brackets) of a declaration block in a rule whose selector matches just the element on which the attribute is set. All URLs in the value must be resolved relative to the element when the attribute is parsed. For the purposes of the CSS cascade, the attribute must be considered to be a 'style' attribute at the author level.

Documents that use style attributes on any of their elements must still be comprehensible and usable if those attributes were removed.

In particular, using the style attribute to hide and show content, or to convey meaning that is otherwise not included in the document, is non-conforming. (To hide and show content, use the hidden attribute.)


element . style

Returns a CSSStyleDeclaration object for the element's style attribute.

The style DOM attribute must return a CSSStyleDeclaration whose value represents the declarations specified in the attribute, if present. Mutating the CSSStyleDeclaration object must create a style attribute on the element (if there isn't one already) and then change its value to be a value representing the serialized form of the CSSStyleDeclaration object. [CSSOM]

In the following example, the words that refer to colors are marked up using the span element and the style attribute to make those words show up in the relevant colors in visual media.

<p>My sweat suit is <span style="color: green; background:
transparent">green</span> and my eyes are <span style="color: blue;
background: transparent">blue</span>.</p>
3.3.3.8 Embedding custom non-visible data

A custom data attribute is an attribute whose name starts with the string "data-", has at least one character after the hyphen, is XML-compatible, has no namespace, and contains no characters in the range U+0041 .. U+005A (LATIN CAPITAL LETTER A .. LATIN CAPITAL LETTER Z).

All attributes in HTML documents get lowercased automatically, so the restriction on uppercase letters doesn't affect such documents.

Custom data attributes are intended to store custom data private to the page or application, for which there are no more appropriate attributes or elements.

These attributes are not intended for use by software that is independent of the site that uses the attributes.

For instance, a site about music could annotate list items representing tracks in an album with custom data attributes containing the length of each track. This information could then be used by the site itself to allow the user to sort the list by track length, or to filter the list for tracks of certain lengths.

<ol>
 <li data-length="2m11s">Beyond The Sea</li>
 ...
</ol>

It would be inappropriate, however, for the user to use generic software not associated with that music site to search for tracks of a certain length by looking at this data.

This is because these attributes are intended for use by the site's own scripts, and are not a generic extension mechanism for publicly-usable metadata.

Every HTML element may have any number of custom data attributes specified, with any value.


element . dataset

Returns a DOMStringMap object for the element's data-* attributes.

The dataset DOM attribute provides convenient accessors for all the data-* attributes on an element. On getting, the dataset DOM attribute must return a DOMStringMap object, associated with the following algorithms, which expose these attributes on their element:

The algorithm for getting the list of name-value pairs
  1. Let list be an empty list of name-value pairs.
  2. For each content attribute on the element whose first five characters are the string "data-", add a name-value pair to list whose name is the attribute's name with the first five character removed and whose value is the attribute's value.
  3. Return list.
The algorithm for setting names to certain values
  1. Let name be the concatenation of the string data- and the name passed to the algorithm.
  2. Let value be the value passed to the algorithm.
  3. Set the value of the attribute with the name name, to the value value, replacing any previous value if the attribute already existed. If setAttribute() would have raised an exception when setting an attribute with the name name, then this must raise the same exception.
The algorithm for deleting names
  1. Let name be the concatenation of the string data- and the name passed to the algorithm.
  2. Remove the attribute with the name name, if such an attribute exists. Do nothing otherwise.

If a Web page wanted an element to represent a space ship, e.g. as part of a game, it would have to use the class attribute along with data-* attributes:

<div class="spaceship" data-id="92432"
     data-weapons="laser 2" data-shields="50%"
     data-x="30" data-y="10" data-z="90">
 <button class="fire"
         onclick="spaceships[this.parentNode.dataset.id].fire()">
  Fire
 </button>
</div>

Authors should carefully design such extensions so that when the attributes are ignored and any associated CSS dropped, the page is still usable.

User agents must not derive any implementation behavior from these attributes or values. Specifications intended for user agents must not define these attributes to have any meaningful values.

3.4 Content models

All the elements in this specification have a defined content model, which describes what nodes are allowed inside the elements, and thus what the structure of an HTML document or fragment must look like.

As noted in the conformance and terminology sections, for the purposes of determining if an element matches its content model or not, CDATASection nodes in the DOM are treated as equivalent to Text nodes, and entity reference nodes are treated as if they were expanded in place.

The space characters are always allowed between elements. User agents represent these characters between elements in the source markup as text nodes in the DOM. Empty text nodes and text nodes consisting of just sequences of those characters are considered inter-element whitespace.

Inter-element whitespace, comment nodes, and processing instruction nodes must be ignored when establishing whether an element matches its content model or not, and must be ignored when following algorithms that define document and element semantics.

An element A is said to be preceded or followed by a second element B if A and B have the same parent node and there are no other element nodes or text nodes (other than inter-element whitespace) between them.

Authors must not use elements in the HTML namespace anywhere except where they are explicitly allowed, as defined for each element, or as explicitly required by other specifications. For XML compound documents, these contexts could be inside elements from other namespaces, if those elements are defined as providing the relevant contexts.

The Atom specification defines the Atom content element, when its type attribute has the value xhtml, as requiring that it contains a single HTML div element. Thus, a div element is allowed in that context, even though this is not explicitly normatively stated by this specification. [ATOM]

In addition, elements in the HTML namespace may be orphan nodes (i.e. without a parent node).

For example, creating a td element and storing it in a global variable in a script is conforming, even though td elements are otherwise only supposed to be used inside tr elements.

var data = {
  name: "Banana",
  cell: document.createElement('td'), 
};

3.4.1 Kinds of content

Each element in HTML falls into zero or more categories that group elements with similar characteristics together. The following broad categories are used in this specification:

These categories are related as follows:

Sectioning content, heading content, phrasing content, and
  embedded content are all types of flow content. Embedded content is
  also a type of phrasing content.

In addition, certain elements are categorized as form-associated elements and further subcategorized to define their role in various form-related processing models.

Some elements have unique requirements and do not fit into any particular category.

3.4.1.1 Metadata content

Metadata content is content that sets up the presentation or behavior of the rest of the content, or that sets up the relationship of the document with other documents, or that conveys other "out of band" information.

Elements from other namespaces whose semantics are primarily metadata-related (e.g. RDF) are also metadata content.

Thus, in the XML serialization, one can use RDF, like this:

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:r="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
 <head>
  <title>Hedral's Home Page</title>
  <r:RDF>
   <Person xmlns="http://www.w3.org/2000/10/swap/pim/contact#"
           r:about="http://hedral.example.com/#">
    <fullName>Cat Hedral</fullName>
    <mailbox r:resource="mailto:hedral@damowmow.com"/>
    <personalTitle>Sir</personalTitle> 
   </Person>
  </r:RDF>
 </head>
 <body>
  <h1>My home page</h1>
  <p>I like playing with string, I guess. Sister says squirrels are fun
  too so sometimes I follow her to play with them.</p>
 </body>
</html>

This isn't possible in the HTML serialization, however.

3.4.1.2 Flow content

Most elements that are used in the body of documents and applications are categorized as flow content.

As a general rule, elements whose content model allows any flow content should have either at least one descendant text node that is not inter-element whitespace, or at least one descendant element node that is embedded content. For the purposes of this requirement, del elements and their descendants must not be counted as contributing to the ancestors of the del element.

This requirement is not a hard requirement, however, as there are many cases where an element can be empty legitimately, for example when it is used as a placeholder which will later be filled in by a script, or when the element is part of a template and would on most pages be filled in but on some pages is not relevant.

3.4.1.3 Sectioning content

Sectioning content is content that defines the scope of headings, footers, and contact information.

Each sectioning content element potentially has a heading and an outline. See the section on headings and sections for further details.

There are also certain elements that are sectioning roots. These are distinct from sectioning content, but they can also have an outline.

3.4.1.4 Heading content

Heading content defines the header of a section (whether explicitly marked up using sectioning content elements, or implied by the heading content itself).

3.4.1.5 Phrasing content

Phrasing content is the text of the document, as well as elements that mark up that text at the intra-paragraph level. Runs of phrasing content form paragraphs.

As a general rule, elements whose content model allows any phrasing content should have either at least one descendant text node that is not inter-element whitespace, or at least one descendant element node that is embedded content. For the purposes of this requirement, nodes that are descendants of del elements must not be counted as contributing to the ancestors of the del element.

Most elements that are categorized as phrasing content can only contain elements that are themselves categorized as phrasing content, not any flow content.

Text nodes that are not inter-element whitespace are phrasing content.

3.4.1.6 Embedded content

Embedded content is content that imports another resource into the document, or content from another vocabulary that is inserted into the document.

Elements that are from namespaces other than the HTML namespace and that convey content but not metadata, are embedded content for the purposes of the content models defined in this specification. (For example, MathML, or SVG.)

Some embedded content elements can have fallback content: content that is to be used when the external resource cannot be used (e.g. because it is of an unsupported format). The element definitions state what the fallback is, if any.

3.4.1.7 Interactive content

Interactive content is content that is specifically intended for user interaction.

Certain elements in HTML have an activation behavior, which means that the user can activate them. This triggers a sequence of events dependent on the activation mechanism, and normally culminating in a click event followed by a DOMActivate event, as described below.

The user agent should allow the user to manually trigger elements that have an activation behavior, for instance using keyboard or voice input, or through mouse clicks. When the user triggers an element with a defined activation behavior in a manner other than clicking it, the default action of the interaction event must be to run synthetic click activation steps on the element.

When a user agent is to run synthetic click activation steps on an element, the user agent must run pre-click activation steps on the element, then fire a click event at the element. The default action of this click event must be to run post-click activation steps on the element. If the event is canceled, the user agent must run canceled activation steps on the element instead.

Given an element target, the nearest activatable element is the element returned by the following algorithm:

  1. If target has a defined activation behavior, then return target and abort these steps.

  2. If target has a parent element, then set target to that parent element and return to the first step.

  3. Otherwise, there is no nearest activatable element.

When a pointing device is clicked, the user agent must run these steps:

  1. Let e be the nearest activatable element of the element designated by the user, if any.

  2. If there is an element e, run pre-click activation steps on it.

  3. Dispatching the required click event.

    Another specification presumably requires the firing of the click event?

    If there is an element e, then the default action of the click event must be to run post-click activation steps on element e.

    If there is an element e but the event is canceled, the user agent must run canceled activation steps on element e.

The above doesn't happen for arbitrary synthetic events dispatched by author script. However, the click() method can be used to make it happen programmatically.

When a user agent is to run post-click activation steps on an element, the user agent must fire a simple event called DOMActivate that is cancelable at that element. The default action of this event must be to run final activation steps on that element. If the event is canceled, the user agent must run canceled activation steps on the element instead.

When a user agent is to run pre-click activation steps on an element, it must run the pre-click activation steps defined for that element, if any.

When a user agent is to run canceled activation steps on an element, it must run the canceled activation steps defined for that element, if any.

When a user agent is to run final activation steps on an element, it must run the activation behavior defined for that element. Activation behaviors can refer to the click and DOMActivate events that were fired by the steps above leading up to this point.

3.4.2 Transparent content models

Some elements are described as transparent; they have "transparent" in the description of their content model.

When a content model includes a part that is "transparent", those parts must not contain content that would not be conformant if all transparent elements in the tree were replaced, in their parent element, by the children in the "transparent" part of their content model, retaining order.

When a transparent element has no parent, then the part of its content model that is "transparent" must instead be treated as accepting any flow content.

3.5 Paragraphs

A paragraph is typically a block of text with one or more sentences that discuss a particular topic, as in typography, but can also be used for more general thematic grouping. For instance, an address is also a paragraph, as is a part of a form, a byline, or a stanza in a poem.

Paragraphs in flow content are defined relative to what the document looks like without the a, ins, del, and map elements complicating matters, since those elements, with their hybrid content models, can straddle paragraph boundaries.

Generally, having elements straddle paragraph boundaries is best avoided. Maintaining such markup can be difficult.

Let view be a view of the DOM that replaces all a, ins, del, and map elements in the document with their contents. Then, in view, for each run of sibling phrasing content nodes uninterrupted by other types of content, in an element that accepts content other than phrasing content, let first be the first node of the run, and let last be the last node of the run. For each such run that consists of at least one node that is neither embedded content nor inter-element whitespace, a paragraph exists in the original DOM from immediately before first to immediately after last. (Paragraphs can thus span across a, ins, del, and map elements.)

Conformance checkers may warn authors of cases where they have paragraphs that overlap each other (this can happen with object, video, audio, and canvas elements).

A paragraph is also formed explicitly by p elements.

The p element can be used to wrap individual paragraphs when there would otherwise not be any content other than phrasing content to separate the paragraphs from each other.

In the following example, there are two paragraphs in a section. There is also a heading, which contains phrasing content that is not a paragraph. Note how the comments and inter-element whitespace do not form paragraphs.

<section>
  <h1>Example of paragraphs</h1>
  This is the <em>first</em> paragraph in this example.
  <p>This is the second.</p>
  <!-- This is not a paragraph. -->
</section>

The following example takes that markup and puts ins and del elements around some of the markup to show that the text was changed (though in this case, the changes admittedly don't make much sense). Notice how this example has exactly the same paragraphs as the previous one, despite the ins and del elements.

<section>
  <ins><h1>Example of paragraphs</h1>
  This is the <em>first</em> paragraph in</ins> this example<del>.
  <p>This is the second.</p></del>
  <!-- This is not a paragraph. -->
</section>

In the following example, the link spans half of the first paragraph, all of the heading separating the two paragraphs, and half of the second paragraph.

<aside>
 Welcome!
 <a href="about.html">
  This is home of...
  <h1>The Falcons!</h1>
  The Lockheed Martin multirole jet fighter aircraft!
 </a>
 This page discusses the F-16 Fighting Falcon's innermost secrets.
</aside>

Here is another way of marking this up, this time showing the paragraphs explicitly, and splitting the one link element into three:

<aside>
 <p>Welcome! <a href="about.html">This is home of...</a></p>
 <h1><a href="about.html">The Falcons!</a></h1>
 <p><a href="about.html">The Lockheed Martin multirole jet
 fighter aircraft!</a> This page discusses the F-16 Fighting
 Falcon's innermost secrets.</p>
</aside>

It is possible for paragraphs to overlap when using certain elements that define fallback content. For example, in the following section:

<section>
 <h1>My Cats</h1>
 You can play with my cat simulator.
 <object data="cats.sim">
  To see the cat simulator, use one of the following links:
  <ul>
   <li><a href="cats.sim">Download simulator file</a>
   <li><a href="http://sims.example.com/watch?v=LYds5xY4INU">Use online simulator</a>
  </ul>
  Alternatively, upgrade to the Mellblom Browser.
 </object>
 I'm quite proud of it.
</section>

There are five paragraphs:

  1. The paragraph that says "You can play with my cat simulator. object I'm quite proud of it.", where object is the object element.
  2. The paragraph that says "To see the cat simulator, use one of the following links:".
  3. The paragraph that says "Download simulator file".
  4. The paragraph that says "Use online simulator".
  5. The paragraph that says "Alternatively, upgrade to the Mellblom Browser.".

The first paragraph is overlapped by the other four. A user agent that supports the "cats.sim" resource will only show the first one, but a user agent that shows the fallback will confusingly show the first sentence of the first paragraph as if it was in the same paragraph as the second one, and will show the last paragraph as if it was at the start of the second sentence of the first paragraph.

To avoid this confusion, explicit p elements can be used.

3.6 APIs in HTML documents

For HTML documents, and for HTML elements in HTML documents, certain APIs defined in DOM3 Core become case-insensitive or case-changing, as sometimes defined in DOM3 Core, and as summarized or required below. [DOM3CORE].

This does not apply to XML documents or to elements that are not in the HTML namespace despite being in HTML documents.

Element.tagName and Node.nodeName

These attributes must return element names converted to uppercase, regardless of the case with which they were created.

Document.createElement()

The canonical form of HTML markup is all-lowercase; thus, this method will lowercase the argument before creating the requisite element. Also, the element created must be in the HTML namespace.

This doesn't apply to Document.createElementNS(). Thus, it is possible, by passing this last method a tag name in the wrong case, to create an element that claims to have the tag name of an element defined in this specification, but doesn't support its interfaces, because it really has another tag name not accessible from the DOM APIs.

Element.setAttribute()
Element.setAttributeNode()

Attribute names are converted to lowercase.

Specifically: when an attribute is set on an HTML element using Element.setAttribute(), the name argument must be converted to lowercase before the element is affected; and when an Attr node is set on an HTML element using Element.setAttributeNode(), it must have its name converted to lowercase before the element is affected.

This doesn't apply to Document.setAttributeNS() and Document.setAttributeNodeNS().

Document.getElementsByTagName()
Element.getElementsByTagName()

These methods (but not their namespaced counterparts) must compare the given argument in an ASCII case-insensitive manner when looking at HTML elements, and in a case-sensitive manner otherwise.

Thus, in an HTML document with nodes in multiple namespaces, these methods will be both case-sensitive and case-insensitive at the same time.

3.7 Dynamic markup insertion

APIs for dynamically inserting markup into the document interact with the parser, and thus their behavior, varies depending on whether they are used with HTML documents (and the HTML parser) or XHTML in XML documents (and the XML parser).

3.7.1 Controlling the input stream

The open() method comes in several variants with different numbers of arguments.

document = document . open( [ type [, replace ] ] )

Causes the Document to be replaced in-place, as if it was a new Document object, but reusing the previous object, which is then returned.

If the type argument is omitted or has the value "text/html", then the resulting Document has an HTML parser associated with it, which can be given data to parse using document.write(). Otherwise, all content passed to document.write() will be parsed as plain text.

If the replace argument is absent or false, a new entry is added to the session history to represent this entry, and the previous entries for this Document are all collapsed into one entry with a new Document object.

The method has no effect if the Document is still being parsed.

window = document . open( url, name, features [, replace ] )

Works like the window.open() method.

document . close()

Closes the input stream that was opened by the document.open() method.

When called with two or fewer arguments, the method must act as follows:

  1. Let type be the value of the first argument, if there is one, or "text/html" otherwise.

  2. Let replace be true if there is a second argument and it is an ASCII case-insensitive match for the value "replace", and false otherwise.

  3. If the document has an active parser that isn't a script-created parser, and the insertion point associated with that parser's input stream is not undefined (that is, it does point to somewhere in the input stream), then the method does nothing. Abort these steps and return the Document object on which the method was invoked.

    This basically causes document.open() to be ignored when it's called in an inline script found during the parsing of data sent over the network, while still letting it have an effect when called asynchronously or on a document that is itself being spoon-fed using these APIs.

  4. Unload the Document object, with the recycle parameter set to true. If the user refused to allow the document to be unloaded, then these steps must be aborted.

  5. If the document has an active parser, then stop that parser, and throw away any pending content in the input stream. what about if it doesn't, because it's either like a text/plain, or Atom, or PDF, or XHTML, or image document, or something?

  6. Unregister all event listeners registered on the Document node and its descendants.

  7. Remove all child nodes of the document, without firing any mutation events.

  8. Replace the Document's singleton objects with new instances of those objects. (This includes in particular the Window, Location, History, ApplicationCache, UndoManager, Navigator, and Selection objects, the various BarProp objects, the two Storage objects, and the various HTMLCollection objects. It also includes all the WebIDL prototypes in the JavaScript binding, including the Document object's prototype.)

  9. Change the document's character encoding to UTF-16.

  10. Change the document's address to the first script's browsing context's active document's address.

  11. Create a new HTML parser and associate it with the document. This is a script-created parser (meaning that it can be closed by the document.open() and document.close() methods, and that the tokenizer will wait for an explicit call to document.close() before emitting an end-of-file token). The encoding confidence is irrelevant.

  12. Mark the document as being an HTML document (it might already be so-marked).
  13. If the type string contains a U+003B SEMICOLON (;) character, remove the first such character and all characters from it up to the end of the string.

    Strip all leading and trailing space characters from type.

    If type is not now an ASCII case-insensitive match for the string "text/html", then act as if the tokenizer had emitted a start tag token with the tag name "pre", then set the HTML parser's tokenization stage's content model flag to PLAINTEXT.

  14. If replace is false, then:

    1. Remove all the entries in the browsing context's session history after the current entry in its Document's History object
    2. Remove any earlier entries that share the same Document
    3. Add a new entry just before the last entry that is associated with the text that was parsed by the previous parser associated with the Document object, as well as the state of the document at the start of these steps. (This allows the user to step backwards in the session history to see the page before it was blown away by the document.open() call.)
  15. Finally, set the insertion point to point at just before the end of the input stream (which at this point will be empty).

  16. Return the Document on which the method was invoked.

When called with three or more arguments, the open() method on the HTMLDocument object must call the open() method on the Window object of the HTMLDocument object, with the same arguments as the original call to the open() method, and return whatever that method returned. If the HTMLDocument object has no Window object, then the method must raise an INVALID_ACCESS_ERR exception.

The close() method must do nothing if there is no script-created parser associated with the document. If there is such a parser, then, when the method is called, the user agent must insert an explicit "EOF" character at the end of the parser's input stream.

3.7.2 document.write()

document . write(text...)

Adds the given string(s) to the Document's input stream. If necessary, calls the open() method implicitly first.

This method throws an INVALID_ACCESS_ERR exception when invoked on XML documents.

The document.write(...) method must act as follows:

  1. If the method was invoked on an XML document, throw an INVALID_ACCESS_ERR exception and abort these steps.

  2. If the insertion point is undefined, the open() method must be called (with no arguments) on the document object. If the user refused to allow the document to be unloaded, then these steps must be aborted. Otherwise, the insertion point will point at just before the end of the (empty) input stream.

  3. The string consisting of the concatenation of all the arguments to the method must be inserted into the input stream just before the insertion point.

  4. If there is a pending external script, then the method must now return without further processing of the input stream.

  5. Otherwise, the tokenizer must process the characters that were inserted, one at a time, processing resulting tokens as they are emitted, and stopping when the tokenizer reaches the insertion point or when the processing of the tokenizer is aborted by the tree construction stage (this can happen if a script end tag token is emitted by the tokenizer).

    If the document.write() method was called from script executing inline (i.e. executing because the parser parsed a set of script tags), then this is a reentrant invocation of the parser.

  6. Finally, the method must return.

3.7.3 document.writeln()

document . writeln(text...)

Adds the given string(s) to the Document's input stream, followed by a newline character. If necessary, calls the open() method implicitly first.

This method throws an INVALID_ACCESS_ERR exception when invoked on XML documents.

The document.writeln(...) method, when invoked, must act as if the document.write() method had been invoked with the same argument(s), plus an extra argument consisting of a string containing a single line feed character (U+000A).

3.7.4 innerHTML

The innerHTML DOM attribute represents the markup of the node's contents.

document . innerHTML [ = value ]

Returns a fragment of HTML or XML that represents the Document.

Can be set, to replace the Document's contents with the result of parsing the given string.

In the case of XML documents, will throw a SYNTAX_ERR if the Document cannot be serialized to XML, or if the given string is not well-formed.

element . innerHTML [ = value ]

Returns a fragment of HTML or XML that represents the element's contents.

Can be set, to replace the contents of the element with nodes parsed from the given string.

In the case of XML documents, will throw a SYNTAX_ERR if the element cannot be serialized to XML, or if the given string is not well-formed.

On getting, if the node's document is an HTML document, then the attribute must return the result of running the HTML fragment serialization algorithm on the node; otherwise, the node's document is an XML document, and the attribute must return the result of running the XML fragment serialization algorithm on the node instead (this might raise an exception instead of returning a string).

On setting, the following steps must be run:

  1. If the node's document is an HTML document: Invoke the HTML fragment parsing algorithm.

    If the node's document is an XML document: Invoke the XML fragment parsing algorithm.

    In either case, the algorithm must be invoked with the string being assigned into the innerHTML attribute as the input. If the node is an Element node, then, in addition, that element must be passed as the context element.

    If this raises an exception, then abort these steps.

    Otherwise, let new children be the nodes returned.

  2. If the attribute is being set on a Document node, and that document has an active HTML parser or XML parser, then stop that parser.

    what about if it doesn't, because it's either like a text/plain, or Atom, or PDF, or XHTML, or image document, or something?

  3. Remove the child nodes of the node whose innerHTML attribute is being set, firing appropriate mutation events.

  4. If the attribute is being set on a Document node, let target document be that Document node. Otherwise, the attribute is being set on an Element node; let target document be the ownerDocument of that Element.

  5. Set the ownerDocument of all the nodes in new children to the target document.

  6. Append all the new children nodes to the node whose innerHTML attribute is being set, preserving their order, and firing mutation events as appropriate.

3.7.5 outerHTML

The outerHTML DOM attribute represents the markup of the element and its contents.

element . outerHTML [ = value ]

Returns a fragment of HTML or XML that represents the element and its contents.

Can be set, to replace the element with nodes parsed from the given string.

In the case of XML documents, will throw a SYNTAX_ERR if the element cannot be serialized to XML, or if the given string is not well-formed.

On getting, if the node's document is an HTML document, then the attribute must return the result of running the HTML fragment serialization algorithm on a fictional node whose only child is the node on which the attribute was invoked; otherwise, the node's document is an XML document, and the attribute must return the result of running the XML fragment serialization algorithm on that fictional node instead (this might raise an exception instead of returning a string).

On setting, the following steps must be run:

  1. Let target be the element whose outerHTML attribute is being set.

  2. If target has no parent node, then abort these steps. There would be no way to obtain a reference to the nodes created even if the remaining steps were run.

  3. If target's parent node is a Document object, throw a NO_MODIFICATION_ALLOWED_ERR exception and abort these steps.

  4. Let parent be target's parent node, unless that is a DocumentFragment node, in which case let parent be an arbitrary body element.

  5. If target's document is an HTML document: Invoke the HTML fragment parsing algorithm.

    If target's document is an XML document: Invoke the XML fragment parsing algorithm.

    In either case, the algorithm must be invoked with the string being assigned into the outerHTML attribute as the input, and parent as the context element.

    If this raises an exception, then abort these steps.

    Otherwise, let new children be targets returned.

  6. Set the ownerDocument of all the nodes in new children to target's document.

  7. Remove target from its parent node, firing mutation events as appropriate, and then insert in its place all the new children nodes, preserving their order, and again firing mutation events as appropriate.

3.7.6 insertAdjacentHTML()

element . insertAdjacentHTML(position, text)

Parsed the given string text as HTML or XML and inserts the resulting nodes into the tree in the position given by the position argument, as follows:

"beforebegin"
Before the element itself.
"afterbegin"
Just inside the element, before its first child.
"beforeend"
Just inside the element, after its last child.
"afterend"
After the element itself.

Throws a SYNTAX_ERR exception the arguments have invalid values (e.g., in the case of XML documents, if the given string is not well-formed).

Throws a NO_MODIFICATION_ALLOWED_ERR exception if the given position isn't possible (e.g. inserting elements after the root element of a Document).

The insertAdjacentHTML(position, text) method, when invoked, must run the following algorithm:

  1. Let position and text be the method's first and second arguments, respectively.

  2. Let target be the element on which the method was invoked.

  3. Use the first matching item from this list:

    If position is an ASCII case-insensitive match for the string "beforebegin"
    If position is an ASCII case-insensitive match for the string "afterend"

    If target has no parent node, then abort these steps.

    If target's parent node is a Document object, then throw a NO_MODIFICATION_ALLOWED_ERR exception and abort these steps.

    Otherwise, let context be the parent node of target.

    If position is an ASCII case-insensitive match for the string "afterbegin"
    If position is an ASCII case-insensitive match for the string "beforeend"

    Let context be the same as target.

    Otherwise

    Throw a SYNTAX_ERR exception.

  4. If target's document is an HTML document: Invoke the HTML fragment parsing algorithm.

    If target's document is an XML document: Invoke the XML fragment parsing algorithm.

    In either case, the algorithm must be invoked with text as the input, and the element selected in by the previous step as the context element.

    If this raises an exception, then abort these steps.

    Otherwise, let new children be targets returned.

  5. Set the ownerDocument of all the nodes in new children to target's document.

  6. Use the first matching item from this list:

    If position is an ASCII case-insensitive match for the string "beforebegin"

    Insert all the new children nodes immediately before target.

    If position is an ASCII case-insensitive match for the string "afterbegin"

    Insert all the new children nodes before the first child of target, if there is one. If there is no such child, append them all to target.

    If position is an ASCII case-insensitive match for the string "beforeend"

    Append all the new children nodes to target.

    If position is an ASCII case-insensitive match for the string "afterend"

    Insert all the new children nodes immediately after target.

    The new children nodes must be inserted in a manner that preserves their order and fires mutation events as appropriate.

4 The elements of HTML

4.1 The root element

4.1.1 The html element

Categories
None.
Contexts in which this element may be used:
As the root element of a document.
Wherever a subdocument fragment is allowed in a compound document.
Content model:
A head element followed by a body element.
Content attributes:
Global attributes
manifest
DOM interface:
Uses HTMLElement.

The html element represents the root of an HTML document.

The manifest attribute gives the address of the document's application cache manifest, if there is one. If the attribute is present, the attribute's value must be a valid URL.

The manifest attribute only has an effect during the early stages of document load. Changing the attribute dynamically thus has no effect (and thus, no DOM API is provided for this attribute).

For the purposes of application cache selection, later base elements cannot affect the resolving of relative URLs in manifest attributes, as the attributes are processed before those elements are seen.

4.2 Document metadata

4.2.1 The head element

Categories
None.
Contexts in which this element may be used:
As the first element in an html element.
Content model:
One or more elements of metadata content, of which exactly one is a title element.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The head element represents a collection of metadata for the Document.

4.2.2 The title element

Categories
Metadata content.
Contexts in which this element may be used:
In a head element containing no other title elements.
Content model:
Text.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The title element represents the document's title or name. Authors should use titles that identify their documents even when they are used out of context, for example in a user's history or bookmarks, or in search results. The document's title is often different from its first heading, since the first heading does not have to stand alone when taken out of context.

There must be no more than one title element per document.

The title element must not contain any elements.

Here are some examples of appropriate titles, contrasted with the top-level headings that might be used on those same pages.

  <title>Introduction to The Mating Rituals of Bees</title>
    ...
  <h1>Introduction</h1>
  <p>This companion guide to the highly successful
  <cite>Introduction to Medieval Bee-Keeping</cite> book is...

The next page might be a part of the same site. Note how the title describes the subject matter unambiguously, while the first heading assumes the reader knows what the context is and therefore won't wonder if the dances are Salsa or Waltz:

  <title>Dances used during bee mating rituals</title>
    ...
  <h1>The Dances</h1>

The string to use as the document's title is given by the document.title DOM attribute. User agents should use the document's title when referring to the document in their user interface.

4.2.3 The base element

Categories
Metadata content.
Contexts in which this element may be used:
In a head element containing no other base elements.
Content model:
Empty.
Content attributes:
Global attributes
href
target
DOM interface:
interface HTMLBaseElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
};

The base element allows authors to specify the document base URL for the purposes of resolving relative URLs, and the name of the default browsing context for the purposes of following hyperlinks. The element does not represent any content beyond this information.

There must be no more than one base element per document.

A base element must have either an href attribute, a target attribute, or both.

The href content attribute, if specified, must contain a valid URL.

A base element, if it has an href attribute, must come before any other elements in the tree that have attributes defined as taking URLs, except the html element (its manifest attribute isn't affected by base elements).

If there are multiple base elements with href attributes, all but the first are ignored.

The target attribute, if specified, must contain a valid browsing context name or keyword, which specifies which browsing context is to be used as the default when hyperlinks and forms in the Document cause navigation.

A base element, if it has a target attribute, must come before any elements in the tree that represent hyperlinks.

If there are multiple base elements with target attributes, all but the first are ignored.

The href and target DOM attributes must reflect the respective content attributes of the same name.

Categories
Metadata content.
Contexts in which this element may be used:
Where metadata content is expected.
In a noscript element that is a child of a head element.
Content model:
Empty.
Content attributes:
Global attributes
href
rel
media
hreflang
type
sizes
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLLinkElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString href;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
           attribute DOMString sizes;
};

The LinkStyle interface must also be implemented by this element, the styling processing model defines how. [CSSOM]

The link element allows authors to link their document to other resources.

The destination of the link(s) is given by the href attribute, which must be present and must contain a valid URL. If the href attribute is absent, then the element does not define a link.

The types of link indicated (the relationships) are given by the value of the rel attribute, which must be present, and must have a value that is a set of space-separated tokens. The allowed values and their meanings are defined in a later section. If the rel attribute is absent, or if the values used are not allowed according to the definitions in this specification, then the element does not define a link.

Two categories of links can be created using the link element. Links to external resources are links to resources that are to be used to augment the current document, and hyperlink links are links to other documents. The link types section defines whether a particular link type is an external resource or a hyperlink. One element can create multiple links (of which some might be external resource links and some might be hyperlinks); exactly which and how many links are created depends on the keywords given in the rel attribute. User agents must process the links on a per-link basis, not a per-element basis.

Each link is handled separately. For instance, if there are two link elements with rel="stylesheet", they each count as a separate external resource, and each is affected by its own attributes independently.

The exact behavior for links to external resources depends on the exact relationship, as defined for the relevant link type. Some of the attributes control whether or not the external resource is to be applied (as defined below). For external resources that are represented in the DOM (for example, style sheets), the DOM representation must be made available even if the resource is not applied. To obtain the resource, the user agent must resolve the URL given by the href attribute, relative to the element, and then fetch the resulting absolute URL. User agents may opt to only fetch such resources when they are needed, instead of pro-actively fetching all the external resources that are not applied.

The semantics of the protocol used (e.g. HTTP) must be followed when fetching external resources. (For example, redirects must be followed and 404 responses must cause the external resource to not be applied.)

Fetching external resources must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined below) has been run.

The task that is queued by the networking task source once the resource has been fetched must, if the loads were successful, queue a task to fire a simple event called load at the link element; otherwise, if the resource or one of its subresources failed to completely load for any reason (e.g. DNS error, HTTP 404 response, a connection being prematurely closed, unsupported Content-Type), it must instead queue a task to fire a simple event called error at the link element. Non-network errors in processing the resource or its subresources (e.g. CSS parse errors, PNG decoding errors) are not failures for the purposes of this paragraph.

The task source for these tasks is the DOM manipulation task source.


Interactive user agents should provide users with a means to follow the hyperlinks created using the link element, somewhere within their user interface. The exact interface is not defined by this specification, but it should include the following information (obtained from the element's attributes, again as defined below), in some form or another (possibly simplified), for each hyperlink created with each link element in the document:

User agents may also include other information, such as the type of the resource (as given by the type attribute).

Hyperlinks created with the link element and its rel attribute apply to the whole page. This contrasts with the rel attribute of a and area elements, which indicates the type of a link whose context is given by the link's location within the document.

The media attribute says which media the resource applies to. The value must be a valid media query. [MQ]

If the link is a hyperlink then the media attribute is purely advisory, and describes for which media the document in question was designed.

However, if the link is an external resource link, then the media attribute is prescriptive. The user agent must apply the external resource to views while their state match the listed media and the other relevant conditions apply, and must not apply them otherwise.

The external resource might have further restrictions defined within that limit its applicability. For example, a CSS style sheet might have some @media blocks. This specification does not override such further restrictions or requirements.

The default, if the media attribute is omitted, is all, meaning that by default links apply to all media.

The hreflang attribute on the link element has the same semantics as the hreflang attribute on hyperlink elements.

The type attribute gives the MIME type of the linked resource. It is purely advisory. The value must be a valid MIME type, optionally with parameters. [RFC2046]

For external resource links, the type attribute is used as a hint to user agents so that they can avoid fetching resources they do not support. If the attribute is present, then the user agent must assume that the resource is of the given type. If the attribute is omitted, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type. If the UA does not support the given MIME type for the given link relationship, then the UA should not fetch the resource; if the UA does support the given MIME type for the given link relationship, then the UA should fetch the resource. If the attribute is omitted, and the external resource link type does not have a default type defined, but the user agent would fetch the resource if the type was known and supported, then the user agent should fetch the resource under the assumption that it will be supported.

User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use the type attribute to determine its actual type. Only the actual type (as defined in the next paragraph) is used to determine whether to apply the resource, not the aforementioned assumed type.

Once the user agent has established the type of the resource, the user agent must apply the resource if it is of a supported type and the other relevant conditions apply, and must ignore the resource otherwise.

If a document contains style sheet links labeled as follows:

<link rel="stylesheet" href="A" type="text/plain">
<link rel="stylesheet" href="B" type="text/css">
<link rel="stylesheet" href="C">

...then a compliant UA that supported only CSS style sheets would fetch the B and C files, and skip the A file (since text/plain is not the MIME type for CSS style sheets).

For files B and C, it would then check the actual types returned by the server. For those that are sent as text/css, it would apply the styles, but for those labeled as text/plain, or any other type, it would not.

If one the two files was returned without a Content-Type metadata, or with a syntactically incorrect type like Content-Type: "null", then the default type for stylesheet links would kick in. Since that default type is text/css, the style sheet would nonetheless be applied.

The title attribute gives the title of the link. With one exception, it is purely advisory. The value is text. The exception is for style sheet links, where the title attribute defines alternative style sheet sets.

The title attribute on link elements differs from the global title attribute of most other elements in that a link without a title does not inherit the title of the parent element: it merely has no title.

The sizes attribute is used with the icon link type. The attribute must not be specified on link elements that do not have a rel attribute that specifies the icon keyword.

Some versions of HTTP defined a Link: header, to be processed like a series of link elements. If supported, for the purposes of ordering links defined by HTTP headers must be assumed to come before any links in the document, in the order that they were given in the HTTP entity header. (URIs in these headers are to be processed and resolved according to the rules given in HTTP; the rules of this specification don't apply.) [HTTP] [RFC2068]

The DOM attributes href, rel, media, hreflang, and type, and sizes each must reflect the respective content attributes of the same name.

The DOM attribute relList must reflect the rel content attribute.

The DOM attribute disabled only applies to style sheet links. When the link element defines a style sheet link, then the disabled attribute behaves as defined for the alternative style sheets DOM. For all other link elements it always return false and does nothing on setting.

4.2.5 The meta element

Categories
Metadata content.
Contexts in which this element may be used:
If the charset attribute is present, or if the element is in the Encoding declaration state: in a head element.
If the http-equiv attribute is present, and the element is not in the Encoding declaration state: in a head element.
If the http-equiv attribute is present, and the element is not in the Encoding declaration state: in a noscript element that is a child of a head element.
If the name attribute is present: where metadata content is expected.
Content model:
Empty.
Content attributes:
Global attributes
name
http-equiv
content
charset
DOM interface:
interface HTMLMetaElement : HTMLElement {
           attribute DOMString content;
           attribute DOMString name;
           attribute DOMString httpEquiv;
};

The meta element represents various kinds of metadata that cannot be expressed using the title, base, link, style, and script elements.

The meta element can represent document-level metadata with the name attribute, pragma directives with the http-equiv attribute, and the file's character encoding declaration when an HTML document is serialized to string form (e.g. for transmission over the network or for disk storage) with the charset attribute.

Exactly one of the name, http-equiv, and charset attributes must be specified.

If either name or http-equiv is specified, then the content attribute must also be specified. Otherwise, it must be omitted.

The charset attribute specifies the character encoding used by the document. This is a character encoding declaration. If the attribute is present in an XML document, its value must be an ASCII case-insensitive match for the string "UTF-8" (and the document is therefore required to use UTF-8 as its encoding).

The charset attribute on the meta element has no effect in XML documents, and is only allowed in order to facilitate migration to and from XHTML.

There must not be more than one meta element with a charset attribute per document.

The content attribute gives the value of the document metadata or pragma directive when the element is used for those purposes. The allowed values depend on the exact context, as described in subsequent sections of this specification.

If a meta element has a name attribute, it sets document metadata. Document metadata is expressed in terms of name/value pairs, the name attribute on the meta element giving the name, and the content attribute on the same element giving the value. The name specifies what aspect of metadata is being set; valid names and the meaning of their values are described in the following sections. If a meta element has no content attribute, then the value part of the metadata name/value pair is the empty string.

If a meta element has the http-equiv attribute specified, it must be either in a head element or in a noscript element that itself is in a head element. If a meta element does not have the http-equiv attribute specified, it must be in a head element.

The DOM attributes name and content must reflect the respective content attributes of the same name. The DOM attribute httpEquiv must reflect the content attribute http-equiv.

4.2.5.1 Standard metadata names

This specification defines a few names for the name attribute of the meta element.

application-name

The value must be a short free-form string that giving the name of the Web application that the page represents. If the page is not a Web application, the application-name metadata name must not be used. User agents may use the application name in UI in preference to the page's title, since the title might include status messages and the like relevant to the status of the page at a particular moment in time instead of just being the name of the application.

description

The value must be a free-form string that describes the page. The value must be appropriate for use in a directory of pages, e.g. in a search engine.

generator

The value must be a free-form string that identifies the software used to generate the document. This value must not be used on hand-authored pages.

4.2.5.2 Other metadata names

Extensions to the predefined set of metadata names may be registered in the WHATWG Wiki MetaExtensions page.

Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time to add a type. These new names must be specified with the following information:

Keyword

The actual name being defined. The name should not be confusingly similar to any other defined name (e.g. differing only in case).

Brief description

A short description of what the metadata name's meaning is, including the format the value is required to be in.

Link to more details
A link to a more detailed description of the metadata name's semantics and requirements. It could be another page on the Wiki, or a link to an external page.
Synonyms

A list of other names that have exactly the same processing requirements. Authors should not use the names defined to be synonyms, they are only intended to allow user agents to support legacy content.

Status

One of the following:

Proposal
The name has not received wide peer review and approval. Someone has proposed it and is using it.
Accepted
The name has received wide peer review and approval. It has a specification that unambiguously defines how to handle pages that use the name, including when they use it in incorrect ways.
Unendorsed
The metadata name has received wide peer review and it has been found wanting. Existing pages are using this keyword, but new pages should avoid it. The "brief description" and "link to more details" entries will give details of what authors should use instead, if anything.

If a metadata name is added with the "proposal" status and found to be redundant with existing values, it should be removed and listed as a synonym for the existing value.

Conformance checkers must use the information given on the WHATWG Wiki MetaExtensions page to establish if a value not explicitly defined in this specification is allowed or not. When an author uses a new type not defined by either this specification or the Wiki page, conformance checkers should offer to add the value to the Wiki, with the details described above, with the "proposal" status.

This specification does not define how new values will get approved. It is expected that the Wiki will have a community that addresses this.

Metadata names whose values are to be URLs must not be proposed or accepted. Links must be represented using the link element, not the meta element.

4.2.5.3 Pragma directives

When the http-equiv attribute is specified on a meta element, the element is a pragma directive.

The http-equiv attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the rows with keywords give the states to which those keywords map. Some of the keywords are non-conforming, as noted in the last column.

State Keywords Notes
Content Language content-language Non-conforming
Encoding declaration content-type
Default style default-style
Refresh refresh

When a meta element is inserted into the document, if its http-equiv attribute is present and represents one of the above states, then the user agent must run the algorithm appropriate for that state, as described in the following list:

Content language

This non-conforming pragma sets the document-wide default language. Until the pragma is successfully processed, there is no document-wide default language.

  1. If another meta element in the Content Language state has already been successfully processed (i.e. when it was inserted the user agent processed it and reached the last step of this list of steps), then abort these steps.

  2. If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.

  3. Let input be the value of the element's content attribute.

  4. Let position point at the first character of input.

  5. Skip whitespace.

  6. Collect a sequence of characters that are neither space characters nor a U+002C COMMA character (",").

  7. Let the document-wide default language be the string that resulted from the previous step.

For meta elements in the Content Language state, the content attribute must have a value consisting of a valid RFC 3066 language code. [RFC3066]

This pragma is not exactly equivalent to the HTTP Content-Language header, for instance it only supports one language. [HTTP]

Encoding declaration state

The Encoding declaration state is just an alternative form of setting the charset attribute: it is a character encoding declaration. This state's user agent requirements are all handled by the parsing section of the specification.

For meta elements in the Encoding declaration state, the content attribute must have a value that is an ASCII case-insensitive match for a string that consists of: the literal string "text/html;", optionally followed by any number of space characters, followed by the literal string "charset=", followed by the character encoding name of the character encoding declaration.

If the document contains a meta element in the Encoding declaration state, then the document must not contain a meta element with the charset attribute present.

The Encoding declaration state may be used in HTML documents only, elements in that state must not be used in XML documents.

Default style state

This pragma sets the name of the default alternative style sheet set.

  1. ...
Refresh state

This pragma acts as timed redirect.

  1. If another meta element in the Refresh state has already been successfully processed (i.e. when it was inserted the user agent processed it and reached the last step of this list of steps), then abort these steps.

  2. If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.

  3. Let input be the value of the element's content attribute.

  4. Let position point at the first character of input.

  5. Skip whitespace.

  6. Collect a sequence of characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, and parse the resulting string using the rules for parsing non-negative integers. If the sequence of characters collected is the empty string, then no number will have been parsed; abort these steps. Otherwise, let time be the parsed number.

  7. Collect a sequence of characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE and U+002E FULL STOP ("."). Ignore any collected characters.

  8. Skip whitespace.

  9. Let url be the address of the current page.

  10. If the character in input pointed to by position is a U+003B SEMICOLON (";"), then advance position to the next character. Otherwise, jump to the last step.

  11. Skip whitespace.

  12. If the character in input pointed to by position is one of U+0055 LATIN CAPITAL LETTER U or U+0075 LATIN SMALL LETTER U, then advance position to the next character. Otherwise, jump to the last step.

  13. If the character in input pointed to by position is one of U+0052 LATIN CAPITAL LETTER R or U+0072 LATIN SMALL LETTER R, then advance position to the next character. Otherwise, jump to the last step.

  14. If the character in input pointed to by position is one of U+004C LATIN CAPITAL LETTER L or U+006C LATIN SMALL LETTER L, then advance position to the next character. Otherwise, jump to the last step.

  15. Skip whitespace.

  16. If the character in input pointed to by position is a U+003D EQUALS SIGN ("="), then advance position to the next character. Otherwise, jump to the last step.

  17. Skip whitespace.

  18. If the character in input pointed to by position is either a U+0027 APOSTROPHE character (') or U+0022 QUOTATION MARK character ("), then let quote be that character, and advance position to the next character. Otherwise, let quote be the empty string.

  19. Let url be equal to the substring of input from the character at position to the end of the string.

  20. If quote is not the empty string, and there is a character in url equal to quote, then truncate url at that character, so that it and all subsequent characters are removed.

  21. Strip any trailing space characters from the end of url.

  22. Strip any U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), and U+000D CARRIAGE RETURN (CR) characters from url.

  23. Resolve the url value to an absolute URL, relative to the meta element. If this fails, abort these steps.

  24. Perform one or more of the following steps:

    • Set a timer so that in time seconds, adjusted to take into account user or user agent preferences, if the user has not canceled the redirect, the user agent navigates the document's browsing context to url, with replacement enabled, and with the document's browsing context as the source browsing context.

    • Provide the user with an interface that, when selected, navigates a browsing context to url, with the document's browsing context as the source browsing context.

    • Do nothing.

    In addition, the user agent may, as with anything, inform the user of any and all aspects of its operation, including the state of any timers, the destinations of any timed redirects, and so forth.

For meta elements in the Refresh state, the content attribute must have a value consisting either of:

In the former case, the integer represents a number of seconds before the page is to be reloaded; in the latter case the integer represents a number of seconds before the page is to be replaced by the page at the given URL.

There must not be more than one meta element with any particular state in the document at a time.

4.2.5.4 Other pragma directives

Extensions to the predefined set of pragma directives may, under certain conditions, be registered in the WHATWG Wiki PragmaExtensions page.

Such extensions must use a name that is identical to a previously-registered HTTP header defined in an RFC, and must have behavior identical to that described for the HTTP header. Pragma directions corresponding to headers describing metadata, or not requiring specific user agent processing, must not be registered; instead, use metadata names. Pragma directions corresponding to headers that affect the HTTP processing model (e.g. caching) must not be registered, as they would result in HTTP-level behavior being different for user agents that implement HTML than for user agents that do not.

Anyone is free to edit the WHATWG Wiki PragmaExtensions page at any time to add a pragma directive satisfying these conditions. Such registrations must specify the following information:

Keyword

The actual name being defined.

Brief description

A short description of the purpose of the pragma directive.

Specification
A link to an IETF RFC defining the corresponding HTTP header.

Conformance checkers must use the information given on the WHATWG Wiki PragmaExtensions page to establish if a value not explicitly defined in this specification is allowed or not.

4.2.5.5 Specifying the document's character encoding

A character encoding declaration is a mechanism by which the character encoding used to store or transmit a document is specified.

The following restrictions apply to character encoding declarations:

If an HTML document does not start with a BOM, and if its encoding is not explicitly given by Content-Type metadata, then the character encoding used must be an ASCII-compatible character encoding, and, in addition, if that encoding isn't US-ASCII itself, then the encoding must be specified using a meta element with a charset attribute or a meta element in the Encoding declaration state.

If an HTML document contains a meta element with a charset attribute or a meta element in the Encoding declaration state, then the character encoding used must be an ASCII-compatible character encoding.

Authors should not use JIS_X0212-1990, x-JIS0208, and encodings based on EBCDIC. Authors should not use UTF-32. Authors must not use the CESU-8, UTF-7, BOCU-1 and SCSU encodings. [CESU8] [UTF7] [BOCU1] [SCSU]

Authors are encouraged to use UTF-8. Conformance checkers may advise against authors using legacy encodings.

In XHTML, the XML declaration should be used for inline character encoding information, if necessary.

4.2.6 The style element

Categories
Metadata content.
If the scoped attribute is present: flow content.
Contexts in which this element may be used:
If the scoped attribute is absent: where metadata content is expected.
If the scoped attribute is absent: in a noscript element that is a child of a head element.
If the scoped attribute is present: where flow content is expected, but before any other flow content other than other style elements and inter-element whitespace.
Content model:
Depends on the value of the type attribute.
Content attributes:
Global attributes
media
type
scoped
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLStyleElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString media;
           attribute DOMString type;
           attribute boolean scoped;
};

The LinkStyle interface must also be implemented by this element, the styling processing model defines how. [CSSOM]

The style element allows authors to embed style information in their documents. The style element is one of several inputs to the styling processing model. The element does not represent content for the user.

If the type attribute is given, it must contain a valid MIME type, optionally with parameters, that designates a styling language. [RFC2046] If the attribute is absent, the type defaults to text/css. [RFC2138]

When examining types to determine if they support the language, user agents must not ignore unknown MIME parameters — types with unknown parameters must be assumed to be unsupported.

The media attribute says which media the styles apply to. The value must be a valid media query. [MQ] User agents must apply the styles to views while their state match the listed media, and must not apply them otherwise.

The styles might be further limited in scope, e.g. in CSS with the use of @media blocks. This specification does not override such further restrictions or requirements.

The default, if the media attribute is omitted, is all, meaning that by default styles apply to all media.

The scoped attribute is a boolean attribute. If set, it indicates that the styles are intended just for the subtree rooted at the style element's parent element, as opposed to the whole Document.

If the scoped attribute is present, then the user agent must apply the specified style information only to the style element's parent element (if any), and that element's child nodes. Otherwise, the specified styles must, if applied, be applied to the entire document.

The title attribute on style elements defines alternative style sheet sets. If the style element has no title attribute, then it has no title; the title attribute of ancestors does not apply to the style element.

The title attribute on style elements, like the title attribute on link elements, differs from the global title attribute in that a style block without a title does not inherit the title of the parent element: it merely has no title.

All descendant elements must be processed, according to their semantics, before the style element itself is evaluated. For styling languages that consist of pure text, user agents must evaluate style elements by passing the concatenation of the contents of all the text nodes that are direct children of the style element (not any other nodes such as comments or elements), in tree order, to the style system. For XML-based styling languages, user agents must pass all the child nodes of the style element to the style system.

All URLs found by the styling language's processor must be resolved, relative to the element (or as defined by the styling language), when the processor is invoked.

Once the element has been evaluated, if it had no subresources or once all the subresources it uses have been fetched, the user agent must queue a task to fire a simple event called load at the style element. If the resource has a subresource that fails to completely load for any reason (e.g. DNS error, HTTP 404 response, the connection being prematurely closed, unsupported Content-Type), the user agent must instead queue a task to fire a simple event called error at the style element. Non-network errors in the processing of the element's contents or its subresources (e.g. CSS parse errors) are not failures for the purposes of this paragraph. The style element must delay the load event of the element's document until one of these tasks has been queued.

The task source for these tasks is the DOM manipulation task source.

This specification does not specify a style system, but CSS is expected to be supported by most Web browsers. [CSS21]

The media, type and scoped DOM attributes must reflect the respective content attributes of the same name.

The DOM disabled attribute behaves as defined for the alternative style sheets DOM.

4.2.7 Styling

The link and style elements can provide styling information for the user agent to use when rendering the document. The DOM Styling specification specifies what styling information is to be used by the user agent and how it is to be used. [CSSOM]

The style and link elements implement the LinkStyle interface. [CSSOM]

For style elements, if the user agent does not support the specified styling language, then the sheet attribute of the element's LinkStyle interface must return null. Similarly, link elements that do not represent external resource links that contribute to the styling processing model (i.e. that do not have a stylesheet keyword in their rel attribute), and link elements whose specified resource has not yet been fetched, or is not in a supported styling language, must have their LinkStyle interface's sheet attribute return null.

Otherwise, the LinkStyle interface's sheet attribute must return a StyleSheet object with the attributes implemented as follows: [CSSOM]

The content type (type DOM attribute)

The content type must be the same as the style's specified type. For style elements, this is the same as the type content attribute's value, or text/css if that is omitted. For link elements, this is the Content-Type metadata of the specified resource.

The location (href DOM attribute)

For link elements, the location must be the result of resolving the URL given by the element's href content attribute, relative to the element, or the empty string if that fails. For style elements, there is no location.

The intended destination media for style information (media DOM attribute)

The media must be the same as the value of the element's media content attribute.

The style sheet title (title DOM attribute)

The title must be the same as the value of the element's title content attribute. If the attribute is absent, then the style sheet does not have a title. The title is used for defining alternative style sheet sets.

The disabled DOM attribute on link and style elements must return false and do nothing on setting, if the sheet attribute of their LinkStyle interface is null. Otherwise, it must return the value of the StyleSheet interface's disabled attribute on getting, and forward the new value to that same attribute on setting.

4.3 Scripting

Scripts allow authors to add interactivity to their documents.

Authors are encouraged to use declarative alternatives to scripting where possible, as declarative mechanisms are often more maintainable, and many users disable scripting.

For example, instead of using script to show or hide a section to show more details, the details element could be used.

Authors are also encouraged to make their applications degrade gracefully in the absence of scripting support.

For example, if an author provides a link in a table header to dynamically resort the table, the link could also be made to function without scripts by requesting the sorted table from the server.

4.3.1 The script element

Categories
Metadata content.
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where metadata content is expected.
Where phrasing content is expected.
Content model:
If there is no src attribute, depends on the value of the type attribute.
If there is a src attribute, the element must be either empty or contain only script documentation.
Content attributes:
Global attributes
src
async
defer
type
charset
DOM interface:
interface HTMLScriptElement : HTMLElement {
           attribute DOMString src;
           attribute boolean async;
           attribute boolean defer;
           attribute DOMString type;
           attribute DOMString charset;
           attribute DOMString text;
};

The script element allows authors to include dynamic script and data blocks in their documents. The element does not represent content for the user.

When used to include dynamic scripts, the scripts may either be embedded inline or may be imported from an external file using the src attribute. If the language is not that described by "text/javascript", then the type attribute must be present. If the type attribute is present, its value must be the type of the script's language.

When used to include data blocks, the data must be embedded inline, the format of the data must be given using the type attribute, and the src attribute must not be specified.

The type attribute gives the language of the script or format of the data. If the attribute is present, its value must be a valid MIME type, optionally with parameters. The charset parameter must not be specified. (The default, which is used if the attribute is absent, is "text/javascript".) [RFC2046]

The src attribute, if specified, gives the address of the external script resource to use. The value of the attribute must be a valid URL identifying a script resource of the type given by the type attribute, if the attribute is present, or of the type "text/javascript", if the attribute is absent.

The charset attribute gives the character encoding of the external script resource. The attribute must not be specified if the src attribute is not present. If the attribute is set, its value must be a valid character encoding name, must be the preferred name for that encoding, and must match the encoding given in the charset parameter of the Content-Type metadata of the external file, if any. [IANACHARSET]

The async and defer attributes are boolean attributes that indicate how the script should be executed.

There are three possible modes that can be selected using these attributes. If the async attribute is present, then the script will be executed asynchronously, as soon as it is available. If the async attribute is not present but the defer attribute is present, then the script is executed when the page has finished parsing. If neither attribute is present, then the script is fetched and executed immediately, before the user agent continues parsing the page. The exact processing details for these attributes is described below.

The defer attribute may be specified even if the async attribute is specified, to cause legacy Web browsers that only support defer (and not async) to fall back to the defer behavior instead of the synchronous blocking behavior that is the default.

Changing the src, type, charset, async, and defer attributes dynamically has no direct effect; these attribute are only used at specific times described below (namely, when the element is inserted into the document).

script elements have four associated pieces of metadata. The first is a flag indicating whether or not the script block has been "already executed". Initially, script elements must have this flag unset (script blocks, when created, are not "already executed"). When a script element is cloned, the "already executed" flag, if set, must be propagated to the clone when it is created. The second is a flag indicating whether the element was "parser-inserted". This flag is set by the HTML parser and is used to handle document.write() calls. The third and fourth pieces of metadata are the script block's type and the script block's character encoding. They are determined when the script is run, based on the attributes on the element at that time.

When a script element that is neither marked as having "already executed" nor marked as being "parser-inserted" experiences one of the events listed in the following list, the user agent must run the script element:

Running a script: When a script element is to be run, the user agent must act as follows:

  1. If either:

    • the script element has a type attribute and its value is the empty string, or
    • the script element has no type attribute but it has a language attribute and that attribute's value is the empty string, or
    • the script element has neither a type attribute nor a language attribute, then

    ...let the script block's type for this script element be "text/javascript".

    Otherwise, if the script element has a type attribute, let the script block's type for this script element be the value of that attribute.

    Otherwise, the element has a non-empty language attribute; let the script block's type for this script element be the concatenation of the string "text/" followed by the value of the language attribute.

    The language attribute is never conforming, and is always ignored if there is a type attribute present.

  2. If the script element has a charset attribute, then let the script block's character encoding for this script element be the encoding given by the charset attribute.

    Otherwise, let the script block's character encoding for this script element be the same as the encoding of the document itself.

  3. If scripting is disabled for the script element, or if the user agent does not support the scripting language given by the script block's type for this script element, then the user agent must abort these steps at this point. The script is not executed.

  4. If the element has no src attribute, and its child nodes consist only of comment nodes and empty text nodes, then the user agent must abort these steps at this point. The script is not executed.

  5. The user agent must set the element's "already executed" flag.

  6. If the element has a src attribute, then the value of that attribute must be resolved relative to the element, and if that is successful, the specified resource must then be fetched.

    For historical reasons, if the URL is a javascript: URL, then the user agent must not, despite the requirements in the definition of the fetching algorithm, actually execute the given script; instead the user agent must act as if it had received an empty HTTP 400 response.

    Once the resource's Content Type metadata is available, if it ever is, apply the algorithm for extracting an encoding from a Content-Type to it. If this returns an encoding, and the user agent supports that encoding, then let the script block's character encoding be that encoding.

    Once the fetching process has completed, and the script has completed loading, the user agent will have to complete the steps described below. (If the parser is still active at that time, those steps defer to the parser to handle the execution of pending scripts.)

    For performance reasons, user agents may start fetching the script as soon as the attribute is set, instead, in the hope that the element will be inserted into the document. Either way, once the element is inserted into the document, the load must have started. If the UA performs such prefetching, but the element is never inserted in the document, or the src attribute is dynamically changed, then the user agent will not execute the script, and the fetching process will have been effectively wasted.

  7. Then, the first of the following options that describes the situation must be followed:

    If the document is still being parsed, and the element has a defer attribute, and the element does not have an async attribute
    The element must be added to the end of the list of scripts that will execute when the document has finished parsing.

    This isn't compatible with IE for inline deferred scripts, but then what IE does is pretty hard to pin down exactly. Do we want to keep this like it is? Be more compatible?

    If the element has an async attribute and a src attribute
    The element must be added to the end of the list of scripts that will execute asynchronously.
    If the element has an async attribute but no src attribute, and the list of scripts that will execute asynchronously is not empty
    The element must be added to the end of the list of scripts that will execute asynchronously.
    If the element has a src attribute and has been flagged as "parser-inserted"
    The element is the pending external script. (There can only be one such script at a time.)
    If the element has a src attribute
    The element must be added to the end of the list of scripts that will execute as soon as possible.
    Otherwise
    The user agent must immediately execute the script block, even if other scripts are already executing.

Fetching an external script must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined below) has been run.

When a script completes loading: If the script element was added to one of the lists mentioned above and the document is still being parsed, then the parser handles it. Otherwise, the UA must run the following steps as the task that the networking task source places on the task queue:

If the script element was added to the list of scripts that will execute when the document has finished parsing:
  1. If the script element is not the first element in the list, then do nothing yet. Stop going through these steps.

  2. Otherwise, execute the script block (the first element in the list).

  3. Remove the script element from the list (i.e. shift out the first entry in the list).

  4. If there are any more entries in the list, and if the script associated with the element that is now the first in the list is already loaded, then jump back to step two to execute it.

If the script element was added to the list of scripts that will execute asynchronously:
  1. If the script is not the first element in the list, then do nothing yet. Stop going through these steps.

  2. Execute the script block (the first element in the list).

  3. Remove the script element from the list (i.e. shift out the first entry in the list).

  4. If there are any more scripts in the list, and the element now at the head of the list had no src attribute when it was added to the list, or had one, but its associated script has finished loading, then jump back to step two to execute the script associated with this element.

If the script element was added to the list of scripts that will execute as soon as possible:
  1. Execute the script block.

  2. Remove the script element from the list.

Executing a script block: When the steps above require that the script block be executed, the user agent must act as follows:

If the load resulted in an error (for example a DNS error, or an HTTP 404 error)

Executing the script block must just consist of firing a simple event called error at the element.

If the load was successful
  1. Initialize the script block's source as follows:

    If the script is from an external file

    The contents of that file, interpreted as string of Unicode characters, are the script source.

    For each of the rows in the following table, starting with the first one and going down, if the file has as many or more bytes available than the number of bytes in the first column, and the first bytes of the file match the bytes given in the first column, then set the script block's character encoding to the encoding given in the cell in the second column of that row, irrespective of any previous value:

    Bytes in Hexadecimal Encoding
    FE FF UTF-16BE
    FF FE UTF-16LE
    EF BB BF UTF-8

    This step looks for Unicode Byte Order Marks (BOMs).

    The file must then be converted to Unicode using the character encoding given by the script block's character encoding.

    If the script is inline and the script block's type is a text-based language

    The value of the DOM text attribute at the time the "running a script" algorithm was first invoked is the script source.

    If the script is inline and the script block's type is an XML-based language

    The child nodes of the script element at the time the "running a script" algorithm was first invoked are the script source.

  2. Create a script from the script element node, using the the script block's source and the the script block's type.

    This is where the script is compiled and actually executed.

  3. Fire a simple event called load at the script element.

The DOM attributes src, type, charset, async, and defer, each must reflect the respective content attributes of the same name.

script . text [ = value ]

Returns the contents of the element, ignoring child nodes that aren't text nodes.

Can be set, to replace the element's children with the given value.

The DOM attribute text must return a concatenation of the contents of all the text nodes that are direct children of the script element (ignoring any other nodes such as comments or elements), in tree order. On setting, it must act the same way as the textContent DOM attribute.

In this example, two script elements are used. One embeds an external script, and the other includes some data.

<script src="game-engine.js"></script>
<script type="text/x-game-map">
........U.........e
o............A....e
.....A.....AAA....e
.A..AAA...AAAAA...e
</script>

The data in this case might be used by the script to generate the map of a video game. The data doesn't have to be used that way, though; maybe the map data is actually embedded in other parts of the page's markup, and the data block here is just used by the site's search engine to help users who are looking for particular features in their game maps.

When inserted using the document.write() method, script elements execute (typically synchronously), but when inserted using innerHTML and outerHTML attributes, they do not execute at all.

4.3.1.1 Scripting languages

A user agent is said to support the scripting language if the script block's type matches the MIME type of a scripting language that the user agent implements.

The following lists some MIME types and the languages to which they refer:

application/ecmascript
application/javascript
application/x-ecmascript
application/x-javascript
text/ecmascript
text/javascript
text/javascript1.0
text/javascript1.1
text/javascript1.2
text/javascript1.3
text/javascript1.4
text/javascript1.5
text/jscript
text/livescript
text/x-ecmascript
text/x-javascript
JavaScript. [ECMA262]
text/javascript;e4x=1
JavaScript with ECMAScript for XML. [ECMA357]

User agents may support other MIME types and other languages.

When examining types to determine if they support the language, user agents must not ignore unknown MIME parameters — types with unknown parameters must be assumed to be unsupported.

4.3.1.2 Inline documentation for external scripts

If a script element's src attribute is specified, then the contents of the script element, if any, must be such that the value of the DOM text attribute, which is derived from the element's contents, matches the documentation production in the following ABNF, the character set for which is Unicode. [ABNF]

documentation = *( *( space / tab / comment ) [ line-comment ] newline )
comment       = slash star *( not-star / star not-slash ) 1*star slash
line-comment  = slash slash *not-newline

; characters
tab           = %x0009 ; U+0009 TAB
newline       = %x000A ; U+000A LINE FEED
space         = %x0020 ; U+0020 SPACE
star          = %x002A ; U+002A ASTERISK
slash         = %x002F ; U+002F SOLIDUS
not-newline   = %x0000-0009 / %x000B-%10FFFF
                ; a Unicode character other than U+000A LINE FEED
not-star      = %x0000-0029 / %x002B-%10FFFF
                ; a Unicode character other than U+002A ASTERISK
not-slash     = %x0000-002E / %x0030-%10FFFF
                ; a Unicode character other than U+002F SOLIDUS

This allows authors to include documentation, such as license information or API information, inside their documents while still referring to external script files. The syntax is constrained so that authors don't accidentally include what looks like valid script while also providing a src attribute.

<script src="cool-effects.js">
 // create new instances using:
 //    var e = new Effect();
 // start the effect using .play, stop using .stop:
 //    e.play();
 //    e.stop();
</script>

4.3.2 The noscript element

Categories
Metadata content.
Flow content.
Phrasing content.
Contexts in which this element may be used:
In a head element of an HTML document, if there are no ancestor noscript elements.
Where phrasing content is expected in HTML documents, if there are no ancestor noscript elements.
Content model:
When scripting is disabled, in a head element: in any order, zero or more link elements, zero or more style elements, and zero or more meta elements.
When scripting is disabled, not in a head element: transparent, but there must be no noscript element descendants.
Otherwise: text that conforms to the requirements given in the prose.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The noscript element represents nothing if scripting is enabled, and represents its children if scripting is disabled. It is used to present different markup to user agents that support scripting and those that don't support scripting, by affecting how the document is parsed.

When used in HTML documents, the allowed content model is as follows:

In a head element, if scripting is disabled for the noscript element

The noscript element must contain only link, style, and meta elements.

In a head element, if scripting is enabled for the noscript element

The noscript element must contain only text, except that invoking the HTML fragment parsing algorithm with the noscript element as the context element and the text contents as the input must result in a list of nodes that consists only of link, style, and meta elements, and no parse errors.

Outside of head elements, if scripting is disabled for the noscript element

The noscript element's content model is transparent, with the additional restriction that a noscript element must not have a noscript element as an ancestor (that is, noscript can't be nested).

Outside of head elements, if scripting is enabled for the noscript element

The noscript element must contain only text, except that the text must be such that running the following algorithm results in a conforming document with no noscript elements and no script elements, and such that no step in the algorithm causes an HTML parser to flag a parse error:

  1. Remove every script element from the document.
  2. Make a list of every noscript element in the document. For every noscript element in that list, perform the following steps:
    1. Let the parent element be the parent element of the noscript element.
    2. Take all the children of the parent element that come before the noscript element, and call these elements the before children.
    3. Take all the children of the parent element that come after the noscript element, and call these elements the after children.
    4. Let s be the concatenation of all the text node children of the noscript element.
    5. Set the innerHTML attribute of the parent element to the value of s. (This, as a side-effect, causes the noscript element to be removed from the document.)
    6. Insert the before children at the start of the parent element, preserving their original relative order.
    7. Insert the after children at the end of the parent element, preserving their original relative order.

All these contortions are required because, for historical reasons, the noscript element is handled differently by the HTML parser based on whether scripting was enabled or not when the parser was invoked. The element is not allowed in XML, because in XML the parser is not affected by such state, and thus the element would not have the desired effect.

The noscript element must not be used in XML documents.

The noscript element is only effective in the HTML serialization, it has no effect in the XML serialization.

The noscript element has no other requirements. In particular, children of the noscript element are not exempt from form submission, scripting, and so forth, even when scripting is enabled for the element.

4.4 Sections

Some elements, for example address elements, are scoped to their nearest ancestor sectioning content. For such elements x, the elements that apply to a sectioning content element e are all the x elements whose nearest sectioning content ancestor is e.

4.4.1 The body element

Categories
Sectioning root.
Contexts in which this element may be used:
As the second element in an html element.
Content model:
Flow content.
Content attributes:
Global attributes
onafterprint
onbeforeprint
onbeforeunload
onblur
onerror
onfocus
onhashchange
onload
onmessage
onoffline
ononline
onpopstate
onredo
onresize
onstorage
onundo
onunload
DOM interface:
interface HTMLBodyElement : HTMLElement {
           attribute Function onafterprint;
           attribute Function onbeforeprint;
           attribute Function onbeforeunload;
           attribute Function onblur;
           attribute Function onerror;
           attribute Function onfocus;
           attribute Function onhashchange;
           attribute Function onload;
           attribute Function onmessage;
           attribute Function onoffline;
           attribute Function ononline;
           attribute Function onpopstate;
           attribute Function onredo;
           attribute Function onresize;
           attribute Function onstorage;
           attribute Function onundo;
           attribute Function onunload;
};

The body element represents the main content of the document.

In conforming documents, there is only one body element. The document.body DOM attribute provides scripts with easy access to a document's body element.

Some DOM operations (for example, parts of the drag and drop model) are defined in terms of "the body element". This refers to a particular element in the DOM, as per the definition of the term, and not any arbitrary body element.

The body element exposes as event handler content attributes a number of the event handler attributes of the Window object. It also mirrors their event handler DOM attributes.

The onerror and onload event handler attributes of the Window object, exposed on the body element, shadow the generic onerror and onload event handler attributes normally supported by HTML elements.

Thus, for example, a bubbling error event fired on a child of the body element of a Document would first trigger the onerror event handler content attributes of that element, then that of the root html element, and only then would it trigger the onerror event handler content attribute on the body element. This is because the event would bubble from the target, to the body, to the html, to the Document, to the Window, and the event handler attribute on the body is watching the Window not the body. A regular event listener attached to the body using addEventListener(), however, would fire when the event bubbled through the body and not when it reaches the Window object.

4.4.2 The section element

Categories
Flow content.
Sectioning content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The section element represents a generic document or application section. A section, in this context, is a thematic grouping of content, typically with a heading, possibly with a footer.

Examples of sections would be chapters, the various tabbed pages in a tabbed dialog box, or the numbered sections of a thesis. A Web site's home page could be split into sections for an introduction, news items, contact information.

In the following example, we see an article (part of a larger Web page) about apples, containing two short sections.

<article>
 <hgroup>
  <h1>Apples</h1>
  <h2>Tasty, delicious fruit!</h2>
 </hgroup>
 <p>The apple is the pomaceous fruit of the apple tree.</p>
 <section>
  <h1>Red Delicious</h1>
  <p>These bright red apples are the most common found in many
  supermarkets.</p>
 </section>
 <section>
  <h1>Granny Smith</h1>
  <p>These juicy, green apples and make a great filling for
  apple pies.</p>
 </section>
</article>

Notice how the use of section means that the author can use h1 elements throughout, without having to worry about whether a particular section is at the top level, the second level, the third level, and so on.

4.4.3 The nav element

Categories
Flow content.
Sectioning content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links. Not all groups of links on a page need to be in a nav element — only sections that consist of primary navigation blocks are appropriate for the nav element. In particular, it is common for footers to have a list of links to various key parts of a site, but the footer element is more appropriate in such cases.

In the following example, the page has several places where links are present, but only one of those places is considered a navigation section.

<body>
 <header>
  <h1>Wake up sheeple!</h1>
  <p><a href="news.html">News</a> -
     <a href="blog.html">Blog</a> -
     <a href="forums.html">Forums</a></p>
  <p>Last Modified: <time>2009-04-01</time></p>
  <nav>
   <h1>Navigation</h1>
   <ul>
    <li><a href="articles.html">Index of all articles</a></li>
    <li><a href="today.html">Things sheeple need to wake up for today</a></li>
    <li><a href="successes.html">Sheeple we have managed to wake</a></li>
   </ul>
  </nav>
 </header>
 <article>
  <p>...page content would be here...</p>
 </article>
 <footer>
  <p>Copyright © 2006 The Example Company</p>
  <p><a href="about.html">About</a> -
     <a href="policy.html">Privacy Policy</a> -
     <a href="contact.html">Contact Us</a></p>
 </footer>
</body>

4.4.4 The article element

Categories
Flow content.
Sectioning content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The article element represents a section of a page that consists of a composition that forms an independent part of a document, page, or site. This could be a forum post, a magazine or newspaper article, a Web log entry, a user-submitted comment, or any other independent item of content.

An article element is "independent" in that its contents could stand alone, for example in syndication. However, the element is still associated with its ancestors; for instance, contact information that applies to a parent body element still covers the article as well.

When article elements are nested, the inner article elements represent articles that are in principle related to the contents of the outer article. For instance, a Web log entry on a site that accepts user-submitted comments could represent the comments as article elements nested within the article element for the Web log entry.

Author information associated with an article element (q.v. the address element) does not apply to nested article elements.

4.4.5 The aside element

Categories
Flow content.
Sectioning content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography.

The following example shows how an aside is used to mark up background material on Switzerland in a much longer news story on Europe.

<aside>
 <h1>Switzerland</h1>
 <p>Switzerland, a land-locked country in the middle of geographic
 Europe, has not joined the geopolitical European Union, though it is
 a signatory to a number of European treaties.</p>
</aside>

The following example shows how an aside is used to mark up a pull quote in a longer article.

...

<p>He later joined a large company, continuing on the same work.
<q>I love my job. People ask me what I do for fun when I'm not at
work. But I'm paid to do my hobby, so I never know what to
answer. Some people wonder what they would do if they didn't have to
work... but I know what I would do, because I was unemployed for a
year, and I filled that time doing exactly what I do
now.</q></p>

<aside>
 <q> People ask me what I do for fun when I'm not at work. But I'm
 paid to do my hobby, so I never know what to answer. </q>
</aside>

<p>Of course his work — or should that be hobby? —
isn't his only passion. He also enjoys other pleasures.</p>

...

4.4.6 The h1, h2, h3, h4, h5, and h6 elements

Categories
Flow content.
Heading content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

These elements represent headings for their sections.

The semantics and meaning of these elements are defined in the section on headings and sections.

These elements have a rank given by the number in their name. The h1 element is said to have the highest rank, the h6 element has the lowest rank, and two elements with the same name have equal rank.

4.4.7 The hgroup element

Categories
Flow content.
Heading content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
One or more h1, h2, h3, h4, h5, and/or h6 elements.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The hgroup element represents the heading of a section. The element is used to group a set of h1h6 elements when the heading has multiple levels, such as subheadings, alternative titles, or taglines.

For the purposes of document summaries, outlines, and the like, the text of hgroup elements is defined to be the text of the highest ranked h1h6 element descendant of the hgroup element, if there are any such elements, and the first such element if there are multiple elements with that rank. If there are no such elements, then the text of the hgroup element is the empty string.

Other elements of heading content in the hgroup element indicate subheadings or subtitles.

The rank of an hgroup element is the same as for an h1 element (the highest rank).

The section on headings and sections defines how hgroup elements are assigned to individual sections.

Here are some examples of valid headings. In each case, the emphasized text represents the text that would be used as the heading in an application extracting heading data and ignoring subheadings.

<hgroup>
 <h1>The reality dysfunction</h1>
 <h2>Space is not the only void</h2>
</hgroup>
<hgroup>
 <h1>Dr. Strangelove</h1>
 <h2>Or: How I Learned to Stop Worrying and Love the Bomb</h2>
</hgroup>

4.4.8 The header element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no header or footer element descendants.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The header element represents a group of introductory or navigational aids. A header element typically contains the section's heading (an h1h6 element or an hgroup element), but can also contain other content, such as a table of contents, a search form, or any relevant logos.

Here are some sample headers. This first one is for a game:

<header>
 <p>Welcome to...</p>
 <h1>Voidwars!</h1>
</header>

The following snippet shows how the element can be used to mark up a specification's header:

<header>
 <hgroup>
  <h1>Scalable Vector Graphics (SVG) 1.2</h1>
  <h2>W3C Working Draft 27 October 2004</h2>
 </hgroup>
 <dl>
  <dt>This version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20041027/">http://www.w3.org/TR/2004/WD-SVG12-20041027/</a></dd>
  <dt>Previous version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20040510/">http://www.w3.org/TR/2004/WD-SVG12-20040510/</a></dd>
  <dt>Latest version of SVG 1.2:</dt>
  <dd><a href="http://www.w3.org/TR/SVG12/">http://www.w3.org/TR/SVG12/</a></dd>
  <dt>Latest SVG Recommendation:</dt>
  <dd><a href="http://www.w3.org/TR/SVG/">http://www.w3.org/TR/SVG/</a></dd>
  <dt>Editor:</dt>
  <dd>Dean Jackson, W3C, <a href="mailto:dean@w3.org">dean@w3.org</a></dd>
  <dt>Authors:</dt>
  <dd>See <a href="#authors">Author List</a></dd>
 </dl>
 <p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notic ...
</header>

The header element is not sectioning content; it doesn't introduce a new section.

In this example, the page has a page heading given by the h1 element, and two subsections whose headings are given by h2 elements. The content after the header element is still part of the last subsection started in the header element, because the header element doesn't take part in the outline algorithm.

<body>
 <header>
  <h1>Little Green Guys With Guns</h1>
  <nav>
   <ul>
    <li><a href="/games">Games</a> |
    <li><a href="/forum">Forum</a> |
    <li><a href="/download">Download</a>
   </ul>
  </nav>
  <h2>Important News</h2> <!-- this starts a second subsection -->
  <!-- this is part of the subsection entitled "Important News" -->
  <p>To play today's games you will need to update your client.</p>
  <h2>Games</h2> <!-- this starts a second subsection -->
 </header>
 <p>You have three active games:</p>
 <!-- this is still part of the subsection entitled "Games" -->
 ...
Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no heading content descendants, no sectioning content descendants, and no header or footer element descendants.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The footer element represents a footer for the section it applies to. A footer typically contains information about its section such as who wrote it, links to related documents, copyright data, and the like.

Contact information for the section to which the footer element applies should be marked up using the address element.

Footers don't necessarily have to appear at the end of a section, though they usually do.

The footer element is inappropriate for containing entire sections. For appendices, indexes, long colophons, verbose license agreements, and other such content which needs sectioning with headings and so forth, regular section elements should be used, not a footer.

Here is a page with two footers, one at the top and one at the bottom, with the same content:

<body>
 <footer><a href="../">Back to index...</a></footer>
 <hgroup>
  <h1>Lorem ipsum</h1>
  <h2>The ipsum of all lorems</h2>
 </hgroup>
 <p>A dolor sit amet, consectetur adipisicing elit, sed do eiusmod
 tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
 veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
 ea commodo consequat. Duis aute irure dolor in reprehenderit in
 voluptate velit esse cillum dolore eu fugiat nulla
 pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
 culpa qui officia deserunt mollit anim id est laborum.</p>
 <footer><a href="../">Back to index...</a></footer>
</body>

4.4.10 The address element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no heading content descendants, no sectioning content descendants, and no header, footer, or address element descendants.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The address element represents the contact information for the section it applies to. If it applies to the body element, then it instead applies to the document as a whole.

For example, a page at the W3C Web site related to HTML might include the following contact information:

<ADDRESS>
 <A href="../People/Raggett/">Dave Raggett</A>, 
 <A href="../People/Arnaud/">Arnaud Le Hors</A>, 
 contact persons for the <A href="Activity">W3C HTML Activity</A>
</ADDRESS>

The address element must not be used to represent arbitrary addresses (e.g. postal addresses), unless those addresses are contact information for the section. (The p element is the appropriate element for marking up such addresses.)

The address element must not contain information other than contact information.

For example, the following is non-conforming use of the address element:

<ADDRESS>Last Modified: 1999/12/24 23:37:50</ADDRESS>

Typically, the address element would be included with other information in a footer element.

To determine the contact information for a sectioning content element (such as a document's body element, which would give the contact information for the page), UAs must collect all the address elements that apply to that sectioning content element and its ancestor sectioning content elements. The contact information is the collection of all the information given by those elements.

Contact information for one sectioning content element, e.g. an aside element, does not apply to its ancestor elements, e.g. the page's body.

4.4.11 Headings and sections

The h1h6 elements and the hgroup element are headings.

The first element of heading content in an element of sectioning content represents the heading for that section. Subsequent headings of equal or higher rank start new (implied) sections, headings of lower rank start implied subsections that are part of the previous one. In both cases, the element represents the heading of the implied section.

Sectioning content elements are always considered subsections of their nearest ancestor element of sectioning content, regardless of what implied sections other headings may have created.

Certain elements are said to be sectioning roots, including blockquote and td elements. These elements can have their own outlines, but the sections and headings inside these elements do not contribute to the outlines of their ancestors.

For the following fragment:

<body>
 <h1>Foo</h1>
 <h2>Bar</h2>
 <blockquote>
  <h3>Bla</h3>
 </blockquote>
 <p>Baz</p>
 <h2>Quux</h2>
 <section>
  <h3>Thud</h3>
 </section>
 <p>Grunt</p>
</body>

...the structure would be:

  1. Foo (heading of explicit body section, containing the "Grunt" paragraph)
    1. Bar (heading starting implied section, containing a block quote and the "Baz" paragraph)
    2. Quux (heading starting implied section)
    3. Thud (heading of explicit section section)

Notice how the section ends the earlier implicit section so that a later paragraph ("Grunt") is back at the top level.

Sections may contain headings of any rank, but authors are strongly encouraged to either use only h1 elements, or to use elements of the appropriate rank for the section's nesting level.

Authors are also encouraged to explicitly wrap sections in elements of sectioning content, instead of relying on the implicit sections generated by having multiple headings in one element of sectioning content.

For example, the following is correct:

<body>
 <h4>Apples</h4>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <h6>Sweet</h6>
  <p>Red apples are sweeter than green ones.</p>
  <h1>Color</h1>
  <p>Apples come in various colors.</p>
 </section>
</body>

However, the same document would be more clearly expressed as:

<body>
 <h1>Apples</h1>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <section>
   <h3>Sweet</h3>
   <p>Red apples are sweeter than green ones.</p>
  </section>
 </section>
 <section>
  <h2>Color</h2>
  <p>Apples come in various colors.</p>
 </section>
</body>

Both of the documents above are semantically identical and would produce the same outline in compliant user agents.

4.4.11.1 Creating an outline

This section defines an algorithm for creating an outline for a sectioning content element or a sectioning root element. It is defined in terms of a walk over the nodes of a DOM tree, in tree order, with each node being visited when it is entered and when it is exited during the walk.

The outline for a sectioning content element or a sectioning root element consists of a list of one or more potentially nested sections. A section is a container that corresponds to some nodes in the original DOM tree. Each section can have one heading associated with it, and can contain any number of further nested sections. The algorithm for the outline also associates each node in the DOM tree with a particular section and potentially a heading. (The sections in the outline aren't section elements, though some may correspond to such elements — they are merely conceptual sections.)

The following markup fragment:

<body>
 <h1>A</h1>
 <p>B</p>
 <h2>C</h2>
 <p>D</p>
 <h2>E</h2>
 <p>F</p>
</body>

...results in the following outline being created for the body node (and thus the entire document):

  1. Section created for body node.

    Associated with heading "A".

    Also associated with paragraph "B".

    Nested sections:

    1. Section implied for first h2 element.

      Associated with heading "C".

      Also associated with paragraph "D".

      No nested sections.

    2. Section implied for second h2 element.

      Associated with heading "E".

      Also associated with paragraph "F".

      No nested sections.

The algorithm that must be followed during a walk of a DOM subtree rooted at a sectioning content element or a sectioning root element to determine that element's outline is as follows:

  1. Let current outlinee be null. (It holds the element whose outline is being created.)

  2. Let current section be null. (It holds a pointer to a section, so that elements in the DOM can all be associated with a section.)

  3. Create a stack to hold elements, which is used to handle nesting. Initialize this stack to empty.

  4. As you walk over the DOM in tree order, trigger the first relevant step below for each element as you enter and exit it.

    If the top of the stack is an element, and you are exiting that element

    The element being exited is a heading content element.

    Pop that element from the stack.

    If the top of the stack is a heading content element

    Do nothing.

    When entering a sectioning content element or a sectioning root element

    If current outlinee is not null, push current outlinee onto the stack.

    Let current outlinee be the element that is being entered.

    Let current section be a newly created section for the current outlinee element.

    Let there be a new outline for the new current outlinee, initialized with just the new current section as the only section in the outline.

    When exiting a sectioning content element, if the stack is not empty

    Pop the top element from the stack, and let the current outlinee be that element.

    Let current section be the last section in the outline of the current outlinee element.

    Append the outline of the sectioning content element being exited to the current section. (This does not change which section is the last section in the outline.)

    When exiting a sectioning root element, if the stack is not empty

    Run these steps:

    1. Pop the top element from the stack, and let the current outlinee be that element.

    2. Let current section be the last section in the outline of the current outlinee element.

    3. Finding the deepest child: If current section has no child sections, stop these steps.

    4. Let current section be the last child section of the current current section.

    5. Go back to the substep labeled finding the deepest child.

    When exiting a sectioning content element or a sectioning root element

    The current outlinee is the element being exited.

    Let current section be the first section in the outline of the current outlinee element.

    Skip to the next step in the overall set of steps. (The walk is over.)

    If the current outlinee is null.

    Do nothing.

    When entering a heading content element

    If the current section has no heading, let the element being entered be the heading for the current section.

    Otherwise, if the element being entered has a rank equal to or greater than the heading of the last section of the outline of the current outlinee, then create a new section and append it to the outline of the current outlinee element, so that this new section is the new last section of that outline. Let current section be that new section. Let the element being entered be the new heading for the current section.

    Otherwise, run these substeps:

    1. Let candidate section be current section.

    2. If the element being entered has a rank lower than the rank of the heading of the candidate section, then create a new section, and append it to candidate section. (This does not change which section is the last section in the outline.) Let current section be this new section. Let the element being entered be the new heading for the current section. Abort these substeps.

    3. Let new candidate section be the section that contains candidate section in the outline of current outlinee.

    4. Let candidate section be new candidate section.

    5. Return to step 2.

    Push the element being entered onto the stack. (This causes the algorithm to skip any descendants of the element.)

    Recall that h1 has the highest rank, and h6 has the lowest rank.

    Otherwise

    Do nothing.

    In addition, whenever you exit a node, after doing the steps above, if current section is not null, associate the node with the section current section.

  5. If the current outlinee is null, then there was no sectioning content element or sectioning root element in the DOM. There is no outline. Abort these steps.

  6. Associate any nodes that were not associated with a section in the steps above with current outlinee as their section.

  7. Associate all nodes with the heading of the section with which they are associated, if any.

  8. If current outlinee is the body element, then the outline created for that element is the outline of the entire document.

The tree of sections created by the algorithm above, or a proper subset thereof, must be used when generating document outlines, for example when generating tables of contents.

When creating an interactive table of contents, entries should jump the user to the relevant sectioning content element, if the section was created for a real element in the original document, or to the relevant heading content element, if the section in the tree was generated for a heading in the above process.

Selecting the first section of the document therefore always takes the user to the top of the document, regardless of where the first heading in the body is to be found.

The following JavaScript function shows how the tree walk could be implemented. The root argument is the root of the tree to walk, and the enter and exit arguments are callbacks that are called with the nodes as they are entered and exited. [ECMA262]

function (root, enter, exit) {
  var node = root;
  start: while (node) {
    enter(node);
    if (node.firstChild) {
      node = node.firstChild;
      continue start;
    }
    while (node) {
      exit(node);
      if (node.nextSibling) {
        node = node.nextSibling;
        continue start;
      }
      if (node == root)
        node = null;
      else
        node = node.parentNode;
    }
  }
}
4.4.11.2 Distinguishing site-wide headings from page headings

Given the outline of a document, but ignoring any sections created for nav and aside elements, and any of their descendants, if the only root of the tree is the body element's section, and it has only a single subsection which is created by an article element, then the heading of the body element should be assumed to be a site-wide heading, and the heading of the article element should be assumed to be the page's heading.

If a page starts with a heading that is common to the whole site, the document must be authored such that, in the document's outline, ignoring any sections created for nav and aside elements and any of their descendants, the tree has only one root section, the body element's section, its heading is the site-wide heading, the body element has just one subsection, that subsection is created by an article element, and that article's heading is the page heading.

If a page does not contain a site-wide heading, then the page must be authored such that, in the document's outline, ignoring any sections created for nav and aside elements and any of their descendants, either the body element has no subsections, or it has more than one subsection, or it has a single subsection but that subsection is not created by an article element, or there is more than one section at the root of the outline.

Conceptually, a site is thus a document with many articles — when those articles are split into many pages, the heading of the original single page becomes the heading of the site, repeated on every page.

4.5 Grouping content

4.5.1 The p element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The p element represents a paragraph.

The following examples are conforming HTML fragments:

<p>The little kitten gently seated himself on a piece of
carpet. Later in his life, this would be referred to as the time the
cat sat on the mat.</p>
<fieldset>
 <legend>Personal information</legend>
 <p>
   <label>Name: <input name="n"></label>
   <label><input name="anon" type="checkbox"> Hide from other users</label>
 </p>
 <p><label>Address: <textarea name="a"></textarea></label></p>
</fieldset>
<p>There was once an example from Femley,<br>
Whose markup was of dubious quality.<br>
The validator complained,<br>
So the author was pained,<br>
To move the error from the markup to the rhyming.</p>

The p element should not be used when a more specific element is more appropriate.

The following example is technically correct:

<section>
 <!-- ... -->
 <p>Last modified: 2001-04-23</p>
 <p>Author: fred@example.com</p>
</section>

However, it would be better marked-up as:

<section>
 <!-- ... -->
 <footer>Last modified: 2001-04-23</footer>
 <address>Author: fred@example.com</address>
</section>

Or:

<section>
 <!-- ... -->
 <footer>
  <p>Last modified: 2001-04-23</p>
  <address>Author: fred@example.com</address>
 </footer>
</section>

4.5.2 The hr element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Empty.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The hr element represents a paragraph-level thematic break, e.g. a scene change in a story, or a transition to another topic within a section of a reference book.

4.5.3 The br element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Empty.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The br element represents a line break.

br elements must be empty. Any content inside br elements must not be considered part of the surrounding text.

br elements must be used only for line breaks that are actually part of the content, as in poems or addresses.

The following example is correct usage of the br element:

<p>P. Sherman<br>
42 Wallaby Way<br>
Sydney</p>

br elements must not be used for separating thematic groups in a paragraph.

The following examples are non-conforming, as they abuse the br element:

<p><a ...>34 comments.</a><br>
<a ...>Add a comment.<a></p>
<p>Name: <input name="name"><br>
Address: <input name="address"></p>

Here are alternatives to the above, which are correct:

<p><a ...>34 comments.</a></p>
<p><a ...>Add a comment.<a></p>
<p>Name: <input name="name"></p>
<p>Address: <input name="address"></p>

If a paragraph consists of nothing but a single br element, it represents a placeholder blank line (e.g. as in a template). Such blank lines must not be used for presentation purposes.

4.5.4 The pre element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The pre element represents a block of preformatted text, in which structure is represented by typographic conventions rather than by elements.

In the HTML serialization, a leading newline character immediately following the pre element start tag is stripped.

Some examples of cases where the pre element could be used:

To represent a block of computer code, the pre element can be used with a code element; to represent a block of computer output the pre element can be used with a samp element. Similarly, the kbd element can be used within a pre element to indicate text that the user is to enter.

In the following snippet, a sample of computer code is presented.

<p>This is the <code>Panel</code> constructor:</p>
<pre><code>function Panel(element, canClose, closeHandler) {
  this.element = element;
  this.canClose = canClose;
  this.closeHandler = function () { if (closeHandler) closeHandler() };
}</code></pre>

In the following snippet, samp and kbd elements are mixed in the contents of a pre element to show a session of Zork I.

<pre><samp>You are in an open field west of a big white house with a boarded
front door.
There is a small mailbox here.

></samp> <kbd>open mailbox</kbd>

<samp>Opening the mailbox reveals:
A leaflet.

></samp></pre>

The following shows a contemporary poem that uses the pre element to preserve its unusual formatting, which forms an intrinsic part of the poem itself.

<pre>                maxling

it is with a          heart
               heavy

that i admit loss of a feline
        so           loved

a friend lost to the
        unknown
                                (night)

~cdr 11dec07</pre>

4.5.5 The dialog element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more pairs of one dt element followed by one dd element.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The dialog element represents a conversation, meeting minutes, a chat transcript, a dialog in a screenplay, an instant message log, or some other construct in which different players take turns in discourse.

Each part of the conversation must have an explicit talker (or speaker) given by a dt element, and a discourse (or quote) given by a dd element.

This example demonstrates this using an extract from Abbot and Costello's famous sketch, Who's on first:

<dialog>
 <dt> Costello
 <dd> Look, you gotta first baseman?
 <dt> Abbott
 <dd> Certainly.
 <dt> Costello
 <dd> Who's playing first?
 <dt> Abbott
 <dd> That's right.
 <dt> Costello
 <dd> When you pay off the first baseman every month, who gets the money?
 <dt> Abbott
 <dd> Every dollar of it. 
</dialog>

Text in a dt element in a dialog element is implicitly the source of the text given in the following dd element, and the contents of the dd element are implicitly a quote from that speaker. There is thus no need to include cite, q, or blockquote elements in this markup. Indeed, a q element inside a dd element in a conversation would actually imply the people talking were themselves quoting another work. See the cite, q, and blockquote elements for other ways to cite or quote.

4.5.6 The blockquote element

Categories
Flow content.
Sectioning root.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
cite
DOM interface:
interface HTMLQuoteElement : HTMLElement {
           attribute DOMString cite;
};

The HTMLQuoteElement interface is also used by the q element.

The blockquote element represents a section that is quoted from another source.

Content inside a blockquote must be quoted from another source, whose address, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a valid URL. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. User agents should allow users to follow such citation links.

The cite DOM attribute must reflect the element's cite content attribute.

The best way to represent a conversation is not with the cite and blockquote elements, but with the dialog element.

This next example shows the use of cite alongside blockquote:

<p>His next piece was the aptly named <cite>Sonnet 130</cite>:</p>
<blockquote cite="http://quotes.example.org/s/sonnet130.html">
  <p>My mistress' eyes are nothing like the sun,<br>
  Coral is far more red, than her lips red,<br>
  ...

4.5.7 The ol element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more li elements.
Content attributes:
Global attributes
reversed
start
DOM interface:
interface HTMLOListElement : HTMLElement {
           attribute boolean reversed;
           attribute long start;
};

The ol element represents a list of items, where the items have been intentionally ordered, such that changing the order would change the meaning of the document.

The items of the list are the li element child nodes of the ol element, in tree order.

The reversed attribute is a boolean attribute. If present, it indicates that the list is a descending list (..., 3, 2, 1). If the attribute is omitted, the list is an ascending list (1, 2, 3, ...).

The start attribute, if present, must be a valid integer giving the ordinal value of the first list item.

If the start attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. The default value, used if the attribute is missing or if the value cannot be converted to a number according to the referenced algorithm, is 1 if the element has no reversed attribute, and is the number of child li elements otherwise.

The first item in the list has the ordinal value given by the ol element's start attribute, unless that li element has a value attribute with a value that can be successfully parsed, in which case it has the ordinal value given by that value attribute.

Each subsequent item in the list has the ordinal value given by its value attribute, if it has one, or, if it doesn't, the ordinal value of the previous item, plus one if the reversed is absent, or minus one if it is present.

The reversed DOM attribute must reflect the value of the reversed content attribute.

The start DOM attribute must reflect the value of the start content attribute.

The following markup shows a list where the order matters, and where the ol element is therefore appropriate. Compare this list to the equivalent list in the ul section to see an example of the same items using the ul element.

<p>I have lived in the following countries (given in the order of when
I first lived there):</p>
<ol>
 <li>Switzerland
 <li>United Kingdom
 <li>United States
 <li>Norway
</ol>

Note how changing the order of the list changes the meaning of the document. In the following example, changing the relative order of the first two items has changed the birthplace of the author:

<p>I have lived in the following countries (given in the order of when
I first lived there):</p>
<ol>
 <li>United Kingdom
 <li>Switzerland
 <li>United States
 <li>Norway
</ol>

4.5.8 The ul element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more li elements.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The ul element represents a list of items, where the order of the items is not important — that is, where changing the order would not materially change the meaning of the document.

The items of the list are the li element child nodes of the ul element.

The following markup shows a list where the order does not matter, and where the ul element is therefore appropriate. Compare this list to the equivalent list in the ol section to see an example of the same items using the ol element.

<p>I have lived in the following countries:</p>
<ul>
 <li>Norway
 <li>Switzerland
 <li>United Kingdom
 <li>United States
</ul>

Note that changing the order of the list does not change the meaning of the document. The items in the snippet above are given in alphabetical order, but in the snippet below they are given in order of the size of their current account balance in 2007, without changing the meaning of the document whatsoever:

<p>I have lived in the following countries:</p>
<ul>
 <li>Switzerland
 <li>Norway
 <li>United Kingdom
 <li>United States
</ul>

4.5.9 The li element

Categories
None.
Contexts in which this element may be used:
Inside ol elements.
Inside ul elements.
Inside menu elements.
Content model:
Flow content.
Content attributes:
Global attributes
If the element is a child of an ol element: value
DOM interface:
interface HTMLLIElement : HTMLElement {
           attribute long value;
};

The li element represents a list item. If its parent element is an ol, ul, or menu element, then the element is an item of the parent element's list, as defined for those elements. Otherwise, the list item has no defined list-related relationship to any other li element.

The value attribute, if present, must be a valid integer giving the ordinal value of the list item.

If the value attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. If the attribute's value cannot be converted to a number, the attribute must be treated as if it was absent. The attribute has no default value.

The value attribute is processed relative to the element's parent ol element (q.v.), if there is one. If there is not, the attribute has no effect.

The value DOM attribute must reflect the value of the value content attribute.

The following example, the top ten movies are listed (in reverse order). Note the way the list is given a title by using a figure element and its legend.

<figure>
 <legend>The top 10 movies of all time</legend>
 <ol>
  <li value="10"><cite>Josie and the Pussycats</cite>, 2001</li>
  <li value="9"><cite lang="sh">Црна мачка, бели мачор</cite>, 1998</li>
  <li value="8"><cite>A Bug's Life</cite>, 1998</li>
  <li value="7"><cite>Toy Story</cite>, 1995</li>
  <li value="6"><cite>Monsters, Inc</cite>, 2001</li>
  <li value="5"><cite>Cars</cite>, 2006</li>
  <li value="4"><cite>Toy Story 2</cite>, 1999</li>
  <li value="3"><cite>Finding Nemo</cite>, 2003</li>
  <li value="2"><cite>The Incredibles</cite>, 2004</li>
  <li value="1"><cite>Ratatouille</cite>, 2007</li>
 </ol>
</figure>

The markup could also be written as follows, using the reversed attribute on the ol element:

<figure>
 <legend>The top 10 movies of all time</legend>
 <ol reversed>
  <li><cite>Josie and the Pussycats</cite>, 2001</li>
  <li><cite lang="sh">Црна мачка, бели мачор</cite>, 1998</li>
  <li><cite>A Bug's Life</cite>, 1998</li>
  <li><cite>Toy Story</cite>, 1995</li>
  <li><cite>Monsters, Inc</cite>, 2001</li>
  <li><cite>Cars</cite>, 2006</li>
  <li><cite>Toy Story 2</cite>, 1999</li>
  <li><cite>Finding Nemo</cite>, 2003</li>
  <li><cite>The Incredibles</cite>, 2004</li>
  <li><cite>Ratatouille</cite>, 2007</li>
 </ol>
</figure>

If the li element is the child of a menu element and itself has a child that defines a command, then the li element will match the :enabled and :disabled pseudo-classes in the same way as the first such child element does.

4.5.10 The dl element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more groups each consisting of one or more dt elements followed by one or more dd elements.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The dl element represents an association list consisting of zero or more name-value groups (a description list). Each group must consist of one or more names (dt elements) followed by one or more values (dd elements).

Name-value groups may be terms and definitions, metadata topics and values, or any other groups of name-value data.

The values within a group are alternatives; multiple paragraphs forming part of the same value must all be given within the same dd element.

The order of the list of groups, and of the names and values within each group, may be significant.

If a dl element is empty, it contains no groups.

If a dl element contains non-whitespace text nodes, or elements other than dt and dd, then those elements or text nodes do not form part of any groups in that dl.

If a dl element contains only dt elements, then it consists of one group with names but no values.

If a dl element contains only dd elements, then it consists of one group with values but no names.

If a dl element starts with one or more dd elements, then the first group has no associated name.

If a dl element ends with one or more dt elements, then the last group has no associated value.

When a dl element doesn't match its content model, it is often due to accidentally using dd elements in the place of dt elements and vice versa. Conformance checkers can spot such mistakes and might be able to advise authors how to correctly use the markup.

In the following example, one entry ("Authors") is linked to two values ("John" and "Luke").

<dl>
 <dt> Authors
 <dd> John
 <dd> Luke
 <dt> Editor
 <dd> Frank
</dl>

In the following example, one definition is linked to two terms.

<dl>
 <dt lang="en-US"> <dfn>color</dfn> </dt>
 <dt lang="en-GB"> <dfn>colour</dfn> </dt>
 <dd> A sensation which (in humans) derives from the ability of
 the fine structure of the eye to distinguish three differently
 filtered analyses of a view. </dd>
</dl>

The following example illustrates the use of the dl element to mark up metadata of sorts. At the end of the example, one group has two metadata labels ("Authors" and "Editors") and two values ("Robert Rothman" and "Daniel Jackson").

<dl>
 <dt> Last modified time </dt>
 <dd> 2004-12-23T23:33Z </dd>
 <dt> Recommended update interval </dt>
 <dd> 60s </dd>
 <dt> Authors </dt>
 <dt> Editors </dt>
 <dd> Robert Rothman </dd>
 <dd> Daniel Jackson </dd>
</dl>

The following example shows the dl element used to give a set of instructions. The order of the instructions here is important (in the other examples, the order of the blocks was not important).

<p>Determine the victory points as follows (use the
first matching case):</p>
<dl>
 <dt> If you have exactly five gold coins </dt>
 <dd> You get five victory points </dd>
 <dt> If you have one or more gold coins, and you have one or more silver coins </dt>
 <dd> You get two victory points </dd>
 <dt> If you have one or more silver coins </dt>
 <dd> You get one victory point </dd>
 <dt> Otherwise </dt>
 <dd> You get no victory points </dd>
</dl>

The following snippet shows a dl element being used as a glossary. Note the use of dfn to indicate the word being defined.

<dl>
 <dt><dfn>Apartment</dfn>, n.</dt>
 <dd>An execution context grouping one or more threads with one or
 more COM objects.</dd>
 <dt><dfn>Flat</dfn>, n.</dt>
 <dd>A deflated tire.</dd>
 <dt><dfn>Home</dfn>, n.</dt>
 <dd>The user's login directory.</dd>
</dl>

The dl element is inappropriate for marking up dialogue. For an example of how to mark up dialogue, see the dialog element.

4.5.11 The dt element

Categories
None.
Contexts in which this element may be used:
Before dd or dt elements inside dl elements.
Before a dd element inside a dialog element.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The dt element represents the term, or name, part of a term-description group in a description list (dl element), and the talker, or speaker, part of a talker-discourse pair in a conversation (dialog element).

The dt element itself, when used in a dl element, does not indicate that its contents are a term being defined, but this can be indicated using the dfn element.

If the dt element is the child of a dialog element, and it further contains a time element, then that time element represents a timestamp for when the associated discourse (dd element) was said, and is not part of the name of the talker.

The following extract shows how an IM conversation log could be marked up.

<dialog>
 <dt> <time>14:22</time> egof
 <dd> I'm not that nerdy, I've only seen 30% of the star trek episodes
 <dt> <time>14:23</time> kaj
 <dd> if you know what percentage of the star trek episodes you have seen, you are inarguably nerdy
 <dt> <time>14:23</time> egof
 <dd> it's unarguably
 <dt> <time>14:24</time> kaj
 <dd> you are not helping your case
</dialog>

4.5.12 The dd element

Categories
None.
Contexts in which this element may be used:
After dt or dd elements inside dl elements.
After a dt element inside a dialog element.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The dd element represents the description, definition, or value, part of a term-description group in a description list (dl element), and the discourse, or quote, part in a conversation (dialog element).

A dl can be used to define a vocabulary list, like in a dictionary. In the following example, each entry, given by a dt with a dfn, has several dds, showing the various parts of the definition.

<dl>
 <dt><dfn>happiness</dfn></dt>
 <dd class="pronunciation">/'hæ p. nes/</dd>
 <dd class="part-of-speech"><i><abbr>n.</abbr></i></dd>
 <dd>The state of being happy.</dd>
 <dd>Good fortune; success. <q>Oh <b>happiness</b>! It worked!</q></dd>
 <dt><dfn>rejoice</dfn></dt>
 <dd class="pronunciation">/ri jois'/</dd>
 <dd><i class="part-of-speech"><abbr>v.intr.</abbr></i> To be delighted oneself.</dd>
 <dd><i class="part-of-speech"><abbr>v.tr.</abbr></i> To cause one to be delighted.</dd>
</dl>

4.5.13 Common grouping idioms

4.5.13.1 Tag clouds

This specification does not define any markup specifically for marking up lists of keywords that apply to a group of pages (also known as tag clouds). In general, authors are encouraged to either mark up such lists using ul elements with explicit inline counts that are then hidden and turned into a presentational effect using a style sheet, or to use SVG.

Here, three tags are included in a short tag cloud:

<style>
@media screen, print, handheld, tv {
  /* should be ignored by non-visual browsers */
  .tag-cloud > li > span { display: none; }
  .tag-cloud > li { display: inline; }
  .tag-cloud-1 { font-size: 0.7em; }
  .tag-cloud-2 { font-size: 0.9em; }
  .tag-cloud-3 { font-size: 1.1em; }
  .tag-cloud-4 { font-size: 1.3em; }
  .tag-cloud-5 { font-size: 1.5em; }
}
</style>
...
<ul class="tag-cloud">
 <li class="tag-cloud-4"><a title="28 instances" href="/t/apple">apple</a> <span>(popular)</span>
 <li class="tag-cloud-2"><a title="6 instances"  href="/t/kiwi">kiwi</a> <span>(rare)</span>
 <li class="tag-cloud-5"><a title="41 instances" href="/t/pear">pear</a> <span>(very popular)</span>
</ul>

The actual frequency of each tag is given using the title attribute. A CSS style sheet is provided to convert the markup into a cloud of differently-sized words, but for user agents that do not support CSS or are not visual, the markup contains annotations like "(popular)" or "(rare)" to categorize the various tags by frequency, thus enabling all users to benefit from the information.

The ul element is used (rather than ol) because the order is not particular important: while the list is in fact ordered alphabetically, it would convey the same information if ordered by, say, the length of the tag.

The tag rel-keyword is not used on these a elements because they do not represent tags that apply to the page itself; they are just part of an index listing the tags themselves.

4.6 Text-level semantics

4.6.1 The a element

Categories
Interactive content.
Flow content.
When the element only contains phrasing content: phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Transparent, but there must be no interactive content descendant.
Content attributes:
Global attributes
href
target
ping
rel
media
hreflang
type
DOM interface:
[Stringifies=href] interface HTMLAnchorElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
           attribute DOMString ping;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;

  // URL decomposition attributes
           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;
};

The Command interface must also be implemented by this element.

If the a element has an href attribute, then it represents a hyperlink (a hypertext anchor).

If the a element has no href attribute, then the element represents a placeholder for where a link might otherwise have been placed, if it had been relevant.

The target, ping, rel, media, hreflang, and type attributes must be omitted if the href attribute is not present.

If a site uses a consistent navigation tool bar on every page, then the link that would normally link to the page itself could be marked up using an a element:

<nav>
 <ul>
  <li> <a href="/">Home</a> </li>
  <li> <a href="/news">News</a> </li>
  <li> <a>Examples</a> </li>
  <li> <a href="/legal">Legal</a> </li>
 </ul>
</nav>

Interactive user agents should allow users to follow hyperlinks created using the a element. The href, target and ping attributes decide how the link is followed. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

The activation behavior of a elements that represent hyperlinks is to run the following steps:

  1. If the DOMActivate event in question is not trusted (i.e. a click() method call was the reason for the event being dispatched), and the a element's target attribute is ... then raise an INVALID_ACCESS_ERR exception and abort these steps.

  2. If the target of the click event is an img element with an ismap attribute specified, then server-side image map processing must be performed, as follows:

    1. If the DOMActivate event was dispatched as the result of a real pointing-device-triggered click event on the img element, then let x be the distance in CSS pixels from the left edge of the image's left border, if it has one, or the left edge of the image otherwise, to the location of the click, and let y be the distance in CSS pixels from the top edge of the image's top border, if it has one, or the top edge of the image otherwise, to the location of the click. Otherwise, let x and y be zero.
    2. Let the hyperlink suffix be a U+003F QUESTION MARK character, the value of x expressed as a base-ten integer using ASCII digits (U+0030 DIGIT ZERO to U+0039 DIGIT NINE), a U+002C COMMA character, and the value of y expressed as a base-ten integer using ASCII digits.
  3. Finally, the user agent must follow the hyperlink defined by the a element. If the steps above defined a hyperlink suffix, then take that into account when following the hyperlink.

The DOM attributes href, ping, target, rel, media, hreflang, and type, must reflect the respective content attributes of the same name.

The DOM attribute relList must reflect the rel content attribute.

The a element also suports the complement of URL decomposition attributes, protocol, host, port, hostname, pathname, search, and hash. These must follow the rules given for URL decomposition attributes, with the input being the result of resolving the element's href attribute relative to the element, if there is such an attribute and resolving it is successful, or the empty string otherwise; and the common setter action being the same as setting the element's href attribute to the new output value.

The a element may be wrapped around entire paragraphs, lists, tables, and so forth, even entire sections, so long as there is no interactive content within (e.g. buttons or other links). This example shows how this can be used to make an entire advertising block into a link:

<aside class="advertising">
 <h1>Advertising</h1>
 <a href="http://ad.example.com/?adid=1929&amp;pubid=1422">
  <section>
   <h1>Mellblomatic 9000!</h1>
   <p>Turn all your widgets into mellbloms!</p>
   <p>Only $9.99 plus shipping and handling.</p>
  </section>
 </a>
 <a href="http://ad.example.com/?adid=375&amp;pubid=1422">
  <section>
   <h1>The Mellblom Browser</h1>
   <p>Web browsing at the speed of light.</p>
   <p>No other browser goes faster!</p>
  </section>
 </a>
</aside>

4.6.2 The q element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
cite
DOM interface:
The q element uses the HTMLQuoteElement interface.

The q element represents some phrasing content quoted from another source.

Quotation punctuation (such as quotation marks) must not appear immediately before, after, or inside q elements; they will be inserted into the rendering by the user agent.

Content inside a q element must be quoted from another source, whose address, if it has one, should be cited in the cite attribute. The source may be fictional, as when quoting characters in a novel or screenplay.

If the cite attribute is present, it must be a valid URL. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. User agents should allow users to follow such citation links.

The q element must not be used in place of quotation marks that do not represent quotes; for example, it is inappropriate to use the q element for marking up sarcastic statements.

The use of q elements to mark up quotations is entirely optional; using explicit quotation punctuation without q elements is just as correct.

Here is a simple example of the use of the q element:

<p>The man said <q>Things that are impossible just take
longer</q>. I disagreed with him.</p>

Here is an example with both an explicit citation link in the q element, and an explicit citation outside:

<p>The W3C page <cite>About W3C</cite> says the W3C's
mission is <q cite="http://www.w3.org/Consortium/">To lead the
World Wide Web to its full potential by developing protocols and
guidelines that ensure long-term growth for the Web</q>. I
disagree with this mission.</p>

In the following example, the quotation itself contains a quotation:

<p>In <cite>Example One</cite>, he writes <q>The man
said <q>Things that are impossible just take longer</q>. I
disagreed with him</q>. Well, I disagree even more!</p>

In the following example, quotation marks are used instead of the q element:

<p>His best argument was ❝I disagree❞, which
I thought was laughable.</p>

In the following example, there is no quote — the quotation marks are used to name a word. Use of the q element in this case would be inappropriate.

<p>The word "ineffable" could have been used to describe the disaster
resulting from the campaign's mismanagement.</p>

4.6.3 The cite element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The cite element represents the title of a work (e.g. a book, a paper, an essay, a poem, a score, a song, a script, a film, a TV show, a game, a sculpture, a painting, a theatre production, a play, an opera, a musical, an exhibition, etc). This can be a work that is being quoted or referenced in detail (i.e. a citation), or it can just be a work that is mentioned in passing.

A person's name is not the title of a work — even if people call that person a piece of work — and the element must therefore not be used to mark up people's names. (In some cases, the b element might be appropriate for names; e.g. in a gossip article where the names of famous people are keywords rendered with a different style to draw attention to them. In other cases, if an element is really needed, the span element can be used.)

A ship is similarly not a work, and the element must not be used to mark up ship names (the i element can be used for that purpose).

This next example shows a typical use of the cite element:

<p>My favorite book is <cite>The Reality Dysfunction</cite> by
Peter F. Hamilton. My favorite comic is <cite>Pearls Before
Swine</cite> by Stephan Pastis. My favorite track is <cite>Jive
Samba</cite> by the Cannonball Adderley Sextet.</p>

This is correct usage:

<p>According to the Wikipedia article <cite>HTML</cite>, as it
stood in mid-February 2008, leaving attribute values unquoted is
unsafe. This is obviously an over-simplification.</p>

The following, however, is incorrect usage, as the cite element here is containing far more than the title of the work:

<!-- do not copy this example, it is an example of bad usage! -->
<p>According to <cite>the Wikipedia article on HTML</cite>, as it
stood in mid-February 2008, leaving attribute values unquoted is
unsafe. This is obviously an over-simplification.</p>

The cite element is obviously a key part of any citation in a bibliography, but it is only used to mark the title:

<p><cite>Universal Declaration of Human Rights</cite>, United Nations,
December 1948.  Adopted by General Assembly resolution 217 A (III).</p>

A citation is not a quote (for which the q element is appropriate).

This is incorrect usage, because cite is not for quotes:

<p><cite>This is wrong!</cite>, said Ian.</p>

This is also incorrect usage, because a person is not a work:

<p><q>This is still wrong!</q>, said <cite>Ian</cite>.</p>

The correct usage does not use a cite element:

<p><q>This is correct</q>, said Ian.</p>

As mentioned above, the b element might be relevant for marking names as being keywords in certain kinds of documents:

<p>And then <b>Ian</b> said <q>this might be right, in a
gossip column, maybe!</q>.</p>

4.6.4 The em element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The em element represents stress emphasis of its contents.

The level of emphasis that a particular piece of content has is given by its number of ancestor em elements.

The placement of emphasis changes the meaning of the sentence. The element thus forms an integral part of the content. The precise way in which emphasis is used in this way depends on the language.

These examples show how changing the emphasis changes the meaning. First, a general statement of fact, with no emphasis:

<p>Cats are cute animals.</p>

By emphasizing the first word, the statement implies that the kind of animal under discussion is in question (maybe someone is asserting that dogs are cute):

<p><em>Cats</em> are cute animals.</p>

Moving the emphasis to the verb, one highlights that the truth of the entire sentence is in question (maybe someone is saying cats are not cute):

<p>Cats <em>are</em> cute animals.</p>

By moving it to the adjective, the exact nature of the cats is reasserted (maybe someone suggested cats were mean animals):

<p>Cats are <em>cute</em> animals.</p>

Similarly, if someone asserted that cats were vegetables, someone correcting this might emphasize the last word:

<p>Cats are cute <em>animals</em>.</p>

By emphasizing the entire sentence, it becomes clear that the speaker is fighting hard to get the point across. This kind of emphasis also typically affects the punctuation, hence the exclamation mark here.

<p><em>Cats are cute animals!</em></p>

Anger mixed with emphasizing the cuteness could lead to markup such as:

<p><em>Cats are <em>cute</em> animals!</em></p>

4.6.5 The strong element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The strong element represents strong importance for its contents.

The relative level of importance of a piece of content is given by its number of ancestor strong elements; each strong element increases the importance of its contents.

Changing the importance of a piece of text with the strong element does not change the meaning of the sentence.

Here is an example of a warning notice in a game, with the various parts marked up according to how important they are:

<p><strong>Warning.</strong> This dungeon is dangerous.
<strong>Avoid the ducks.</strong> Take any gold you find.
<strong><strong>Do not take any of the diamonds</strong>,
they are explosive and <strong>will destroy anything within
ten meters.</strong></strong> You have been warned.</p>

4.6.6 The small element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The small element represents small print or other side comments.

Small print is typically legalese describing disclaimers, caveats, legal restrictions, or copyrights. Small print is also sometimes used for attribution.

The small element does not "de-emphasize" or lower the importance of text emphasized by the em element or marked as important with the strong element.

In this example the footer contains contact information and a copyright.

<footer>
 <address>
  For more details, contact
  <a href="mailto:js@example.com">John Smith</a>.
 </address>
 <p><small>© copyright 2038 Example Corp.</small></p>
</footer>

In this second example, the small element is used for a side comment in an article.

<p>Example Corp today announced record profits for the
second quarter <small>(Full Disclosure: Foo News is a subsidiary of
Example Corp)</small>, leading to speculation about a third quarter
merger with Demo Group.</p>

This is distinct from a sidebar, which might be multiple paragraphs long and is removed from the main flow of text. In the following example, we see a sidebar from the same article. This sidebar also has small print, indicating the source of the information in the sidebar.

<aside>
 <h1>Example Corp</h1>
 <p>This company mostly creates small software and Web
 sites.</p>
 <p>The Example Corp company mission is "To provide entertainment
 and news on a sample basis".</p>
 <p><small>Information obtained from <a
 href="http://example.com/about.html">example.com</a> home
 page.</small></p>
</aside>

In this last example, the small element is marked as being important small print.

<p><strong><small>Continued use of this service will result in a kiss.</small></strong></p>

4.6.7 The mark element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The mark element represents a run of text in one document marked or highlighted for reference purposes, due to its relevance in another context. When used in a quotation or other block of text referred to from the prose, it indicates a highlight that was not originally present but which has been added to bring the reader's attention to a part of the text that might not have been considered important by the original author when the block was originally written, but which is now under previously unexpected scrutiny. When used in the main prose of a document, it indicates a part of the document that has been highlighted due to its likely relevance to the user's current activity.

This example shows how the mark element can be used to bring attention to a particular part of a quotation:

<p lang="en-US">Consider the following quote:</p>
<blockquote lang="en-GB">
 <p>Look around and you will find, no-one's really
 <mark>colour</mark> blind.</p>
</blockquote>
<p lang="en-US">As we can tell from the <em>spelling</em> of the word,
the person writing this quote is clearly not American.</p>

Another example of the mark element is highlighting parts of a document that are matching some search string. If someone looked at a document, and the server knew that the user was searching for the word "kitten", then the server might return the document with one paragraph modified as follows:

<p>I also have some <mark>kitten</mark>s who are visiting me
these days. They're really cute. I think they like my garden! Maybe I
should adopt a <mark>kitten</mark>.</p>

In the following snippet, a paragraph of text refers to a specific part of a code fragment.

<p>The highlighted part below is where the error lies:</p>
<pre><code>var i: Integer;
begin
   i := <mark>1.1</mark>;
end.</code></pre>

This is another example showing the use of mark to highlight a part of quoted text that was originally not emphasized. In this example, common typographic conventions have led the author to explicitly style mark elements in quotes to render in italics.

<article>
 <style>
  blockquote mark, q mark {
    font: inherit; font-style: italic;
    text-decoration: none;
    background: transparent; color: inherit;
  }
  .bubble em {
    font: inherit; font-size: larger;
    text-decoration: underline;
  }
 </style>
 <h1>She knew</h1>
 <p>Did you notice the subtle joke in the joke on panel 4?</p>
 <blockquote>
  <p class="bubble">I didn't <em>want</em> to believe. <mark>Of course
  on some level I realized it was a known-plaintext attack.</mark> But I
  couldn't admit it until I saw for myself.</p>
 </blockquote>
 <p>(Emphasis mine.) I thought that was great. It's so pedantic, yet it
 explains everything neatly.</p>
</article>

Note, incidentally, the distinction between the em element in this example, which is part of the original text being quoted, and the mark element, which is highlighting a part for comment.

The following example shows the difference between denoting the importance of a span of text (strong) as opposed to denoting the relevance of a span of text (mark). It is an extract from a textbook, where the extract has had the parts relevant to the exam highlighted. The safety warnings, important though they may be, are apparently not relevant to the exam.

<h3>Wormhole Physics Introduction</h3>

<p><mark>A wormhole in normal conditions can be held open for a
maximum of just under 39 minutes.</mark> Conditions that can increase
the time include a powerful energy source coupled to one or both of
the gates connecting the wormhole, and a large gravity well (such as a
black hole).</p>

<p><mark>Momentum is preserved across the wormhole. Electromagnetic
radiation can travel in both directions through a wormhole,
but matter cannot.</mark></p>

<p>When a wormhole is created, a vortex normally forms.
<strong>Warning: The vortex caused by the wormhole opening will
annihilate anything in its path.</strong> Vortexes can be avoided when
using sufficiently advanced dialing technology.</p>

<p><mark>An obstruction in a gate will prevent it from accepting a
wormhole connection.</mark></p>

4.6.8 The dfn element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content, but there must be no descendant dfn elements.
Content attributes:
Global attributes
Also, the title attribute has special semantics on this element.
DOM interface:
Uses HTMLElement.

The dfn element represents the defining instance of a term. The paragraph, description list group, or section that is the nearest ancestor of the dfn element must also contain the definition(s) for the term given by the dfn element.

Defining term: If the dfn element has a title attribute, then the exact value of that attribute is the term being defined. Otherwise, if it contains exactly one element child node and no child text nodes, and that child element is an abbr element with a title attribute, then the exact value of that attribute is the term being defined. Otherwise, it is the exact textContent of the dfn element that gives the term being defined.

If the title attribute of the dfn element is present, then it must contain only the term being defined.

The title attribute of ancestor elements does not affect dfn elements.

An a element that links to a dfn element represents an instance of the term defined by the dfn element.

In the following fragment, the term "GDO" is first defined in the first paragraph, then used in the second.

<p>The <dfn><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <abbr title="Garage Door Opener">GDO</abbr>
and so Hammond ordered the iris to be opened.</p>

With the addition of an a element, the reference can be made explicit:

<p>The <dfn id=gdo><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <a href=#gdo><abbr title="Garage Door Opener">GDO</abbr></a>
and so Hammond ordered the iris to be opened.</p>

4.6.9 The abbr element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
Also, the title attribute has special semantics on this element.
DOM interface:
Uses HTMLElement.

The abbr element represents an abbreviation or acronym, optionally with its expansion. The title attribute may be used to provide an expansion of the abbreviation. The attribute, if specified, must contain an expansion of the abbreviation, and nothing else.

The paragraph below contains an abbreviation marked up with the abbr element. This paragraph defines the term "Web Hypertext Application Technology Working Group".

<p>The <dfn id=whatwg><abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr></dfn>
is a loose unofficial collaboration of Web browser manufacturers and
interested parties who wish to develop new technologies designed to
allow authors to write and deploy Applications over the World Wide
Web.</p>

An alternative way to write this would be:

<p>The <dfn id=whatwg>Web Hypertext Application Technology
Working Group</dfn> (<abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr>)
is a loose unofficial collaboration of Web browser manufacturers and
interested parties who wish to develop new technologies designed to
allow authors to write and deploy Applications over the World Wide
Web.</p>

This paragraph has two abbreviations. Notice how only one is defined; the other, with no expansion associated with it, does not use the abbr element.

<p>The
<abbr title="Web Hypertext Application Technology Working Group">WHATWG</abbr>
started working on HTML5 in 2004.</p>

This paragraph links an abbreviation to its definition.

<p>The <a href="#whatwg"><abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr></a>
community does not have much representation from Asia.</p>

This paragraph marks up an abbreviation without giving an expansion, possibly as a hook to apply styles for abbreviations (e.g. smallcaps).

<p>Philip` and Dashiva both denied that they were going to
get the issue counts from past revisions of the specification to
backfill the <abbr>WHATWG</abbr> issue graph.</p>

If an abbreviation is pluralized, the expansion's grammatical number (plural vs singular) must match the grammatical number of the contents of the element.

Here the plural is outside the element, so the expansion is in the singular:

<p>Two <abbr title="Working Group">WG</abbr>s worked on
this specification: the <abbr>WHATWG</abbr> and the
<abbr>HTMLWG</abbr>.</p>

Here the plural is inside the element, so the expansion is in the plural:

<p>Two <abbr title="Working Groups">WGs</abbr> worked on
this specification: the <abbr>WHATWG</abbr> and the
<abbr>HTMLWG</abbr>.</p>

Abbreviations do not have to be marked up using this element. It is expected to be useful in the following cases:

Providing an expansion in a title attribute once will not necessarily cause other abbr elements in the same document with the same contents but without a title attribute to behave as if they had the same expansion. Every abbr element is independent.

4.6.10 The time element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
datetime
DOM interface:
interface HTMLTimeElement : HTMLElement {
           attribute DOMString dateTime;
  readonly attribute Date date;
  readonly attribute Date time;
  readonly attribute Date timezone;
};

The time element represents a precise date and/or a time in the proleptic Gregorian calendar. [GREGORIAN]

This element is intended as a way to encode modern dates and times in a machine-readable way so that user agents can offer to add them to the user's calendar. For example, adding birthday reminders or scheduling events.

The time element is not intended for encoding times for which a precise date or time cannot be established. For example, it would be inappropriate for encoding times like "one millisecond after the big bang", "the early part of the Jurassic period", or "a winter around 250 BCE".

For dates before the introduction of the Gregorian calendar, authors are encouraged to not use the time element, or else to be very careful about converting dates and times from the period to the Gregorian calendar. This is complicated by the way the Gregorian calendar was phased in at different times in different countries, ranging from part way through the 16th century all the way to early in the 20th.

The datetime attribute, if present, must contain a valid date or time string that identifies the date or time being specified.

If the datetime attribute is not present, then the date or time must be specified in the content of the element, such that the element's textContent is a valid date or time string in content, and the date, if any, must be expressed using the Gregorian calendar.

If the datetime attribute is present, then the element may be empty, in which case the user agent should convey the attribute's value to the user when rendering the element.

The time element can be used to encode dates, for example in Microformats. The following shows a hypothetical way of encoding an event using a variant on hCalendar that uses the time element:

<div class="vevent">
 <a class="url" href="http://www.web2con.com/">http://www.web2con.com/</a>
  <span class="summary">Web 2.0 Conference</span>:
  <time class="dtstart" datetime="2007-10-05">October 5</time> -
  <time class="dtend" datetime="2007-10-20">19</time>,
  at the <span class="location">Argent Hotel, San Francisco, CA</span>
 </div>

The time element is not necessary for encoding dates or times. In the following snippet, the time is encoded using time, so that it can be restyled (e.g. using XBL2) to match local conventions, while the year is not marked up at all, since marking it up would not be particularly useful.

<p>I usually have a snack at <time>16:00</time>.</p>
<p>I've liked model trains since at least 1983.</p>

Using a styling technology that supports restyling times, the first paragraph from the above snippet could be rendered as follows:

I usually have a snack at 4pm.

Or it could be rendered as follows:

I usually have a snack at 16h00.

The dateTime DOM attribute must reflect the datetime content attribute.

User agents, to obtain the date, time, and time zone represented by a time element, must follow these steps:

  1. If the datetime attribute is present, then use the rules to parse a date or time string with the flag in attribute from the value of that attribute, and let the result be result.
  2. Otherwise, use the rules to parse a date or time string with the flag in content from the element's textContent, and let the result be result.
  3. If result is empty (because the parsing failed), then the date is unknown, the time is unknown, and the time zone is unknown.
  4. Otherwise: if result contains a date, then that is the date; if result contains a time, then that is the time; and if result contains a time zone, then the time zone is the element's time zone. (A time zone can only be present if both a date and a time are also present.)
time . date

Returns a Date object representing the date component of the element's value, at midnight in the UTC time zone.

Returns null if there is no date.

time . time

Returns a Date object representing the time component of the element's value, on 1970-01-01 in the UTC time zone.

Returns null if there is no time.

time . timezone

Returns a Date object representing the time corresponding to 1970-01-01 00:00 UTC in the time zone given by the element's value.

Returns null if there is no time zone.

The date DOM attribute must return null if the date is unknown, and otherwise must return the time corresponding to midnight UTC (i.e. the first second) of the given date.

The time DOM attribute must return null if the time is unknown, and otherwise must return the time corresponding to the given time of 1970-01-01, with the time zone UTC.

The timezone DOM attribute must return null if the time zone is unknown, and otherwise must return the time corresponding to 1970-01-01 00:00 UTC in the given time zone, with the time zone set to UTC (i.e. the time corresponding to 1970-01-01 at 00:00 UTC plus the offset corresponding to the time zone).

In the following snippet:

<p>Our first date was <time datetime="2006-09-23">a Saturday</time>.</p>

...the time element's date attribute would have the value 1,158,969,600,000ms, and the time and timezone attributes would return null.

In the following snippet:

<p>We stopped talking at <time datetime="2006-09-24T05:00-07:00">5am the next morning</time>.</p>

...the time element's date attribute would have the value 1,159,056,000,000ms, the time attribute would have the value 18,000,000ms, and the timezone attribute would return −25,200,000ms. To obtain the actual time, the three attributes can be added together, obtaining 1,159,048,800,000, which is the specified date and time in UTC.

Finally, in the following snippet:

<p>Many people get up at <time>08:00</time>.</p>

...the time element's date attribute would have the value null, the time attribute would have the value 28,800,000ms, and the timezone attribute would return null.

4.6.11 The progress element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
value
max
DOM interface:
interface HTMLProgressElement : HTMLElement {
           attribute float value;
           attribute float max;
  readonly attribute float position;
};

The progress element represents the completion progress of a task. The progress is either indeterminate, indicating that progress is being made but that it is not clear how much more work remains to be done before the task is complete (e.g. because the task is waiting for a remote host to respond), or the progress is a number in the range zero to a maximum, giving the fraction of work that has so far been completed.

There are two attributes that determine the current task completion represented by the element.

The value attribute specifies how much of the task has been completed, and the max attribute specifies how much work the task requires in total. The units are arbitrary and not specified.

Instead of using the attributes, authors are recommended to include the current value and the maximum value inline as text inside the element.

Here is a snippet of a Web application that shows the progress of some automated task:

<section>
 <h2>Task Progress</h2>
 <p>Progress: <progress><span id="p">0</span>%</progress></p>
 <script>
  var progressBar = document.getElementById('p');
  function updateProgress(newValue) {
    progressBar.textContent = newValue;
  }
 </script>
</section>

(The updateProgress() method in this example would be called by some other code on the page to update the actual progress bar as the task progressed.)

Author requirements: The max and value attributes, when present, must have values that are valid floating point numbers. The max attribute, if present, must have a value greater than zero. The value attribute, if present, must have a value equal to or greater than zero, and less than or equal to the value of the max attribute, if present, or 1, otherwise.

The progress element is the wrong element to use for something that is just a gauge, as opposed to task progress. For instance, indicating disk space usage using progress would be inappropriate. Instead, the meter element is available for such use cases.

User agent requirements: User agents must parse the max and value attributes' values according to the rules for parsing floating point number values.

If the value attribute is omitted, then user agents must also parse the textContent of the progress element in question using the steps for finding one or two numbers of a ratio in a string. These steps will return nothing, one number, one number with a denominator punctuation character, or two numbers.

Using the results of this processing, user agents must determine whether the progress bar is an indeterminate progress bar, or whether it is a determinate progress bar, and in the latter case, what its current and maximum values are, all as follows:

  1. If the max attribute is omitted, and the value is omitted, and the results of parsing the textContent was nothing, then the progress bar is an indeterminate progress bar. Abort these steps.
  2. Otherwise, it is a determinate progress bar.
  3. If the max attribute is included, then, if a value could be parsed out of it, then the maximum value is that value.
  4. Otherwise, if the max attribute is absent but the value attribute is present, or, if the max attribute is present but no value could be parsed from it, then the maximum is 1.
  5. Otherwise, if neither attribute is included, then, if the textContent contained one number with an associated denominator punctuation character, then the maximum value is the value associated with that denominator punctuation character; otherwise, if the textContent contained two numbers, the maximum value is the higher of the two values; otherwise, the maximum value is 1.
  6. If the value attribute is present on the element and a value could be parsed out of it, that value is the current value of the progress bar. Otherwise, if the attribute is present but no value could be parsed from it, the current value is zero.
  7. Otherwise if the value attribute is absent and the max attribute is present, then, if the textContent was parsed and found to contain just one number, with no associated denominator punctuation character, then the current value is that number. Otherwise, if the value attribute is absent and the max attribute is present then the current value is zero.
  8. Otherwise, if neither attribute is present, then the current value is the lower of the one or two numbers that were found in the textContent of the element.
  9. If the maximum value is less than or equal to zero, then it is reset to 1.
  10. If the current value is less than zero, then it is reset to zero.
  11. Finally, if the current value is greater than the maximum value, then the current value is reset to the maximum value.

UA requirements for showing the progress bar: When representing a progress element to the user, the UA should indicate whether it is a determinate or indeterminate progress bar, and in the former case, should indicate the relative position of the current value relative to the maximum value.

The max and value DOM attributes must reflect the respective content attributes of the same name. When the relevant content attributes are absent, the DOM attributes must return zero. The value parsed from the textContent never affects the DOM values.

progress . position

For a determinate progress bar (one with known current and maximum values), returns the result of dividing the current value by the maximum value.

For an indeterminate progress bar, returns −1.

If the progress bar is an indeterminate progress bar, then the position DOM attribute must return −1. Otherwise, it must return the result of dividing the current value by the maximum value.

4.6.12 The meter element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
value
min
low
high
max
optimum
DOM interface:
interface HTMLMeterElement : HTMLElement {
           attribute float value;
           attribute float min;
           attribute float max;
           attribute float low;
           attribute float high;
           attribute float optimum;
};

The meter element represents a scalar measurement within a known range, or a fractional value; for example disk usage, the relevance of a query result, or the fraction of a voting population to have selected a particular candidate.

This is also known as a gauge.

The meter element should not be used to indicate progress (as in a progress bar). For that role, HTML provides a separate progress element.

The meter element also does not represent a scalar value of arbitrary range — for example, it would be wrong to use this to report a weight, or height, unless there is a known maximum value.

There are six attributes that determine the semantics of the gauge represented by the element.

The min attribute specifies the lower bound of the range, and the max attribute specifies the upper bound. The value attribute specifies the value to have the gauge indicate as the "measured" value.

The other three attributes can be used to segment the gauge's range into "low", "medium", and "high" parts, and to indicate which part of the gauge is the "optimum" part. The low attribute specifies the range that is considered to be the "low" part, and the high attribute specifies the range that is considered to be the "high" part. The optimum attribute gives the position that is "optimum"; if that is higher than the "high" value then this indicates that the higher the value, the better; if it's lower than the "low" mark then it indicates that lower values are better, and naturally if it is in between then it indicates that neither high nor low values are good.

Authoring requirements: The recommended way of giving the value is to include it as contents of the element, either as two numbers (the higher number represents the maximum, the other number the current value, and the minimum is assumed to be zero), or as a percentage or similar (using one of the characters such as "%"), or as a fraction. However, it is also possible to use the attributes to specify these values.

One of the following conditions, along with all the requirements that are listed with that condition, must be met:

There are exactly two numbers in the contents of the element, and the value, min, and max attributes are all omitted

If specified, the low, high, and optimum attributes must have values greater than or equal to zero and less than or equal to the bigger of the two numbers in the contents of the element.

If both the low and high attributes are specified, then the low attribute's value must be less than or equal to the value of the high attribute.

There is exactly one number followed by zero or more White_Space characters and a valid denominator punctuation character in the contents of the element, and the value, min, and max attributes are all omitted

If specified, the low, high, and optimum attributes must have values greater than or equal to zero and less than or equal to the value associated with the denominator punctuation character.

If both the low and high attributes are specified, then the low attribute's value must be less than or equal to the value of the high attribute.

There is exactly one number in the contents of the element, and the value attribute is omitted
There are no numbers in the contents of the element, and the value attribute is specified

If the min attribute attribute is specified, then the minimum is that attribute's value; otherwise, it is 0.

If the max attribute attribute is specified, then the maximum is that attribute's value; otherwise, it is 1.

If there is exactly one number in the contents of the element, then value is that number; otherwise, value is the value of the value attribute.

The following inequalities must hold, as applicable:

If both the low and high attributes are specified, then the low attribute's value must be less than or equal to the value of the high attribute.

For the purposes of these requirements, a number is a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally including with a single U+002E FULL STOP character (.), and separated from other numbers by at least one character that isn't any of those; interpreted as a base ten number.

The value, min, low, high, max, and optimum attributes, when present, must have values that are valid floating point numbers.

If no minimum or maximum is specified, then the range is assumed to be 0..1, and the value thus has to be within that range.

The following examples all represent a measurement of three quarters (of the maximum of whatever is being measured):

<meter>75%</meter>
<meter>750‰</meter>
<meter>3/4</meter>
<meter>6 blocks used (out of 8 total)</meter>
<meter>max: 100; current: 75</meter>
<meter><object data="graph75.png">0.75</object></meter>
<meter min="0" max="100" value="75"></meter>

The following example is incorrect use of the element, because it doesn't give a range (and since the default maximum is 1, both of the gauges would end up looking maxed out):

<p>The grapefruit pie had a radius of <meter>12cm</meter>
and a height of <meter>2cm</meter>.</p> <!-- BAD! -->

Instead, one would either not include the meter element, or use the meter element with a defined range to give the dimensions in context compared to other pies:

<p>The grapefruit pie had a radius of 12cm and a height of
2cm.</p>
<dl>
 <dt>Radius: <dd> <meter min=0 max=20 value=12>12cm</meter>
 <dt>Height: <dd> <meter min=0 max=10 value=2>2cm</meter>
</dl>

There is no explicit way to specify units in the meter element, but the units may be specified in the title attribute in free-form text.

The example above could be extended to mention the units:

<dl>
 <dt>Radius: <dd> <meter min=0 max=20 value=12 title="centimeters">12cm</meter>
 <dt>Height: <dd> <meter min=0 max=10 value=2 title="centimeters">2cm</meter>
</dl>

User agent requirements: User agents must parse the min, max, value, low, high, and optimum attributes using the rules for parsing floating point number values.

If the value attribute has been omitted, the user agent must also process the textContent of the element according to the steps for finding one or two numbers of a ratio in a string. These steps will return nothing, one number, one number with a denominator punctuation character, or two numbers.

User agents must then use all these numbers to obtain values for six points on the gauge, as follows. (The order in which these are evaluated is important, as some of the values refer to earlier ones.)

The minimum value

If the min attribute is specified and a value could be parsed out of it, then the minimum value is that value. Otherwise, the minimum value is zero.

The maximum value

If the max attribute is specified and a value could be parsed out of it, the maximum value is that value.

Otherwise, if the max attribute is specified but no value could be parsed out of it, or if it was not specified, but either or both of the min or value attributes were specified, then the maximum value is 1.

Otherwise, none of the max, min, and value attributes were specified. If the result of processing the textContent of the element was either nothing or just one number with no denominator punctuation character, then the maximum value is 1; if the result was one number but it had an associated denominator punctuation character, then the maximum value is the value associated with that denominator punctuation character; and finally, if there were two numbers parsed out of the textContent, then the maximum is the higher of those two numbers.

If the above machinations result in a maximum value less than the minimum value, then the maximum value is actually the same as the minimum value.

The actual value

If the value attribute is specified and a value could be parsed out of it, then that value is the actual value.

If the value attribute is not specified but the max attribute is specified and the result of processing the textContent of the element was one number with no associated denominator punctuation character, then that number is the actual value.

If neither of the value and max attributes are specified, then, if the result of processing the textContent of the element was one number (with or without an associated denominator punctuation character), then that is the actual value, and if the result of processing the textContent of the element was two numbers, then the actual value is the lower of the two numbers found.

Otherwise, if none of the above apply, the actual value is zero.

If the above procedure results in an actual value less than the minimum value, then the actual value is actually the same as the minimum value.

If, on the other hand, the result is an actual value greater than the maximum value, then the actual value is the maximum value.

The low boundary

If the low attribute is specified and a value could be parsed out of it, then the low boundary is that value. Otherwise, the low boundary is the same as the minimum value.

If the low boundary is then less than the minimum value, then the low boundary is actually the same as the minimum value. Similarly, if the low boundary is greater than the maximum value, then it is actually the maximum value instead.

The high boundary

If the high attribute is specified and a value could be parsed out of it, then the high boundary is that value. Otherwise, the high boundary is the same as the maximum value.

If the high boundary is then less than the low boundary, then the high boundary is actually the same as the low boundary. Similarly, if the high boundary is greater than the maximum value, then it is actually the maximum value instead.

The optimum point

If the optimum attribute is specified and a value could be parsed out of it, then the optimum point is that value. Otherwise, the optimum point is the midpoint between the minimum value and the maximum value.

If the optimum point is then less than the minimum value, then the optimum point is actually the same as the minimum value. Similarly, if the optimum point is greater than the maximum value, then it is actually the maximum value instead.

All of which will result in the following inequalities all being true:

UA requirements for regions of the gauge: If the optimum point is equal to the low boundary or the high boundary, or anywhere in between them, then the region between the low and high boundaries of the gauge must be treated as the optimum region, and the low and high parts, if any, must be treated as suboptimal. Otherwise, if the optimum point is less than the low boundary, then the region between the minimum value and the low boundary must be treated as the optimum region, the region between the low boundary and the high boundary must be treated as a suboptimal region, and the region between the high boundary and the maximum value must be treated as an even less good region. Finally, if the optimum point is higher than the high boundary, then the situation is reversed; the region between the high boundary and the maximum value must be treated as the optimum region, the region between the high boundary and the low boundary must be treated as a suboptimal region, and the remaining region between the low boundary and the minimum value must be treated as an even less good region.

UA requirements for showing the gauge: When representing a meter element to the user, the UA should indicate the relative position of the actual value to the minimum and maximum values, and the relationship between the actual value and the three regions of the gauge.

The following markup:

<h3>Suggested groups</h3>
<menu type="toolbar">
 <a href="?cmd=hsg" onclick="hideSuggestedGroups()">Hide suggested groups</a>
</menu>
<ul>
 <li>
  <p><a href="/group/comp.infosystems.www.authoring.stylesheets/view">comp.infosystems.www.authoring.stylesheets</a> -
     <a href="/group/comp.infosystems.www.authoring.stylesheets/subscribe">join</a></p>
  <p>Group description: <strong>Layout/presentation on the WWW.</strong></p>
  <p><meter value="0.5">Moderate activity,</meter> Usenet, 618 subscribers</p>
 </li>
 <li>
  <p><a href="/group/netscape.public.mozilla.xpinstall/view">netscape.public.mozilla.xpinstall</a> -
     <a href="/group/netscape.public.mozilla.xpinstall/subscribe">join</a></p>
  <p>Group description: <strong>Mozilla XPInstall discussion.</strong></p>
  <p><meter value="0.25">Low activity,</meter> Usenet, 22 subscribers</p>
 </li>
 <li>
  <p><a href="/group/mozilla.dev.general/view">mozilla.dev.general</a> -
     <a href="/group/mozilla.dev.general/subscribe">join</a></p>
  <p><meter value="0.25">Low activity,</meter> Usenet, 66 subscribers</p>
 </li>
</ul>

Might be rendered as follows:

With the <meter> elements rendered as inline green bars of varying lengths.

User agents may combine the value of the title attribute and the other attributes to provide context-sensitive help or inline text detailing the actual values.

For example, the following snippet:

<meter min=0 max=60 value=23.2 title=seconds></meter>

...might cause the user agent to display a gauge with a tooltip saying "Value: 23.2 out of 60." on one line and "seconds" on a second line.

The min, max, value, low, high, and optimum DOM attributes must reflect the respective content attributes of the same name. When the relevant content attributes are absent, the DOM attributes must return zero. The value parsed from the textContent never affects the DOM values.

4.6.13 The code element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The code element represents a fragment of computer code. This could be an XML element name, a filename, a computer program, or any other string that a computer would recognize.

Although there is no formal way to indicate the language of computer code being marked up, authors who wish to mark code elements with the language used, e.g. so that syntax highlighting scripts can use the right rules, may do so by adding a class prefixed with "language-" to the element.

The following example shows how the element can be used in a paragraph to mark up element names and computer code, including punctuation.

<p>The <code>code</code> element represents a fragment of computer
code.</p>

<p>When you call the <code>activate()</code> method on the
<code>robotSnowman</code> object, the eyes glow.</p>

<p>The example below uses the <code>begin</code> keyword to indicate
the start of a statement block. It is paired with an <code>end</code>
keyword, which is followed by the <code>.</code> punctuation character
(full stop) to indicate the end of the program.</p>

The following example shows how a block of code could be marked up using the pre and code elements.

<pre><code class="language-pascal">var i: Integer;
begin
   i := 1;
end.</code></pre>

A class is used in that example to indicate the language used.

See the pre element for more details.

4.6.14 The var element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The var element represents a variable. This could be an actual variable in a mathematical expression or programming context, or it could just be a term used as a placeholder in prose.

In the paragraph below, the letter "n" is being used as a variable in prose:

<p>If there are <var>n</var> pipes leading to the ice
cream factory then I expect at <em>least</em> <var>n</var>
flavors of ice cream to be available for purchase!</p>

For mathematics, in particular for anything beyond the simplest of expressions, MathML is more appropriate. However, the var element can still be used to refer to specific variables that are then mentioned in MathML expressions.

In this example, an equation is shown, with a legend that references the variables in the equation. The expression itself is marked up with MathML, but the variables are mentioned in the figure's legend using var.

<figure>
 <math>
  <mi>a</mi>
  <mo>=</mo>
  <msqrt>
   <msup><mi>b</mi><mn>2</mn></msup>
   <mi>+</mi>
   <msup><mi>c</mi><mn>2</mn></msup>
  </msqrt>
 </math>
 <legend> 
  Using Pythagoras' theorem to solve for the hypotenuse <var>a</var> of
  a triangle with sides <var>b</var> and <var>c</var>
 </legend>
</figure>

4.6.15 The samp element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The samp element represents (sample) output from a program or computing system.

See the pre and kbd elements for more details.

This example shows the samp element being used inline:

<p>The computer said <samp>Too much cheese in tray
two</samp> but I didn't know what that meant.</p>

This second example shows a block of sample output. Nested samp and kbd elements allow for the styling of specific elements of the sample output using a style sheet.

<pre><samp><samp class="prompt">jdoe@mowmow:~$</samp> <kbd>ssh demo.example.com</kbd>
Last login: Tue Apr 12 09:10:17 2005 from mowmow.example.com on pts/1
Linux demo 2.6.10-grsec+gg3+e+fhs6b+nfs+gr0501+++p3+c4a+gr2b-reslog-v6.189 #1 SMP Tue Feb 1 11:22:36 PST 2005 i686 unknown

<samp class="prompt">jdoe@demo:~$</samp> <samp class="cursor">_</samp></samp></pre>

4.6.16 The kbd element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The kbd element represents user input (typically keyboard input, although it may also be used to represent other input, such as voice commands).

When the kbd element is nested inside a samp element, it represents the input as it was echoed by the system.

When the kbd element contains a samp element, it represents input based on system output, for example invoking a menu item.

When the kbd element is nested inside another kbd element, it represents an actual key or other single unit of input as appropriate for the input mechanism.

Here the kbd element is used to indicate keys to press:

<p>To make George eat an apple, press <kbd><kbd>Shift</kbd>+<kbd>F3</kbd></kbd></p>

In this second example, the user is told to pick a particular menu item. The outer kbd element marks up a block of input, with the inner kbd elements representing each individual step of the input, and the samp elements inside them indicating that the steps are input based on something being displayed by the system, in this case menu labels:

<p>To make George eat an apple, select
    <kbd><kbd><samp>File</samp></kbd>|<kbd><samp>Eat Apple...</samp></kbd></kbd>
</p>

4.6.17 The sub and sup elements

Categories
Flow content.
Phrasing content.
Contexts in which these elements may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The sup element represents a superscript and the sub element represents a subscript.

These elements must be used only to mark up typographical conventions with specific meanings, not for typographical presentation for presentation's sake. For example, it would be inappropriate for the sub and sup elements to be used in the name of the LaTeX document preparation system. In general, authors should use these elements only if the absence of those elements would change the meaning of the content.

When the sub element is used inside a var element, it represents the subscript that identifies the variable in a family of variables.

<p>The coordinate of the <var>i</var>th point is
(<var>x<sub><var>i</var></sub></var>, <var>y<sub><var>i</var></sub></var>).
For example, the 10th point has coordinate
(<var>x<sub>10</sub></var>, <var>y<sub>10</sub></var>).</p>

In certain languages, superscripts are part of the typographical conventions for some abbreviations.

<p>The most beautiful women are
<span lang="fr"><abbr>M<sup>lle</sup></abbr> Gwendoline</span> and 
<span lang="fr"><abbr>M<sup>me</sup></abbr> Denise</span>.</p>

Mathematical expressions often use subscripts and superscripts. Authors are encouraged to use MathML for marking up mathematics, but authors may opt to use sub and sup if detailed mathematical markup is not desired. [MathML]

<var>E</var>=<var>m</var><var>c</var><sup>2</sup>
f(<var>x</var>, <var>n</var>) = log<sub>4</sub><var>x</var><sup><var>n</var></sup>

4.6.18 The span element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The span element doesn't mean anything on its own, but can be useful when used together with other attributes, e.g. class, lang, or dir. It represents its children.

4.6.19 The i element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The i element represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, a ship name, or some other prose whose typical typographic presentation is italicized.

Terms in languages different from the main text should be annotated with lang attributes (xml:lang in XML).

The examples below show uses of the i element:

<p>The <i class="taxonomy">Felis silvestris catus</i> is cute.</p>
<p>The term <i>prose content</i> is defined above.</p>
<p>There is a certain <i lang="fr">je ne sais quoi</i> in the air.</p>

In the following example, a dream sequence is marked up using i elements.

<p>Raymond tried to sleep.</p>
<p><i>The ship sailed away on Thursday</i>, he
dreamt. <i>The ship had many people aboard, including a beautiful
princess called Carey. He watched her, day-in, day-out, hoping she
would notice him, but she never did.</i></p>
<p><i>Finally one night he picked up the courage to speak with
her—</i></p>
<p>Raymond woke with a start as the fire alarm rang out.</p>

Authors are encouraged to use the class attribute on the i element to identify why the element is being used, so that if the style of a particular use (e.g. dream sequences as opposed to taxonomic terms) is to be changed at a later date, the author doesn't have to go through the entire document (or series of related documents) annotating each use. Similarly, authors are encouraged to consider whether other elements might be more applicable than the i element, for instance the em element for marking up stress emphasis, or the dfn element to mark up the defining instance of a term.

Style sheets can be used to format i elements, just like any other element can be restyled. Thus, it is not the case that content in i elements will necessarily be italicized.

4.6.20 The b element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The b element represents a span of text to be stylistically offset from the normal prose without conveying any extra importance, such as key words in a document abstract, product names in a review, or other spans of text whose typical typographic presentation is boldened.

The following example shows a use of the b element to highlight key words without marking them up as important:

<p>The <b>frobonitor</b> and <b>barbinator</b> components are fried.</p>

In the following example, objects in a text adventure are highlighted as being special by use of the b element.

<p>You enter a small room. Your <b>sword</b> glows
brighter. A <b>rat</b> scurries past the corner wall.</p>

Another case where the b element is appropriate is in marking up the lede (or lead) sentence or paragraph. The following example shows how a BBC article about kittens adopting a rabbit as their own could be marked up using HTML5 elements:

<article>
 <h2>Kittens 'adopted' by pet rabbit</h2>
 <p><b>Six abandoned kittens have found an unexpected new
 mother figure — a pet rabbit.</b></p>
 <p>Veterinary nurse Melanie Humble took the three-week-old
 kittens to her Aberdeen home.</p>
[...]

The b element should be used as a last resort when no other element is more appropriate. In particular, headings should use the h1 to h6 elements, stress emphasis should use the em element, importance should be denoted with the strong element, and text marked or highlighted should use the mark element.

The following would be incorrect usage:

<p><b>WARNING!</b> Do not frob the barbinator!</p>

In the previous example, the correct element to use would have been strong, not b.

Style sheets can be used to format b elements, just like any other element can be restyled. Thus, it is not the case that content in b elements will necessarily be boldened.

4.6.21 The bdo element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
Also, the dir global attribute has special semantics on this element.
DOM interface:
Uses HTMLElement.

The bdo element represents explicit text directionality formatting control for its children. It allows authors to override the Unicode bidi algorithm by explicitly specifying a direction override. [BIDI]

Authors must specify the dir attribute on this element, with the value ltr to specify a left-to-right override and with the value rtl to specify a right-to-left override.

If the element has the dir attribute set to the exact value ltr, then for the purposes of the bidi algorithm, the user agent must act as if there was a U+202D LEFT-TO-RIGHT OVERRIDE character at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at the end of the element.

If the element has the dir attribute set to the exact value rtl, then for the purposes of the bidi algorithm, the user agent must act as if there was a U+202E RIGHT-TO-LEFT OVERRIDE character at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at the end of the element.

The requirements on handling the bdo element for the bidi algorithm may be implemented indirectly through the style layer. For example, an HTML+CSS user agent should implement these requirements by implementing the CSS 'unicode-bidi' property. [CSS21]

4.6.22 The ruby element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
One or more groups of: phrasing content followed either by a single rt element, or an rp element, an rt element, and another rp element.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The ruby element allows one or more spans of phrasing content to be marked with ruby annotations. Ruby annotations are short runs of text presented alongside base text, primarily used in East Asian typography as a guide for pronunciation or to include other annotations. In Japanese, this form of typography is also known as furigana.

A ruby element represents the spans of phrasing content it contains, ignoring all the child rt and rp elements and their descendants. Those spans of phrasing content have associated annotations created using the rt element.

In this example, each ideograph in the Japanese text 漢字 is annotated with its kanji reading.

... 
<ruby>
 漢 <rt> かん </rt>
 字 <rt> じ  </rt>
</ruby>
...

This might be rendered as:

The two main ideographs, each with its kanji annotation rendered in a smaller font above it.

In this example, each ideograph in the traditional Chinese text 漢字 is annotated with its bopomofo reading.

<ruby>
 漢 <rt> ㄏㄢˋ </rt>
 字 <rt> ㄗˋ  </rt>
</ruby>

This might be rendered as:

The two main ideographs, each with its bopomofo annotation rendered in a smaller font next to it.

In this example, each ideograph in the simplified Chinese text 汉字 is annotated with its pinyin reading.

...
<ruby>
 汉 <rt> hàn </rt>
 字 <rt> zì  </rt>
</ruby>
...

This might be rendered as:

The two main ideographs, each with its pinyin annotation rendered in a smaller font above it.

4.6.23 The rt element

Categories
None.
Contexts in which this element may be used:
As a child of a ruby element.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The rt element marks the ruby text component of a ruby annotation.

An rt element that is a child of a ruby element represents an annotation (given by its children) for the zero or more nodes of phrasing content that immediately precedes it in the ruby element, ignoring rp elements.

An rt element that is not a child of a ruby element represents the same thing as its children.

4.6.24 The rp element

Categories
None.
Contexts in which this element may be used:
As a child of a ruby element, either immediately before or immediately after an rt element.
Content model:
If the rp element is immediately after an rt element that is immediately preceded by another rp element: a single character from Unicode character class Pe.
Otherwise: a single character from Unicode character class Ps.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The rp element can be used to provide parentheses around a ruby text component of a ruby annotation, to be shown by user agents that don't support ruby annotations.

An rp element that is a child of a ruby element represents nothing and its contents must be ignored. An rp element whose parent element is not a ruby element represents its children.

The example above, in which each ideograph in the text 漢字 is annotated with its kanji reading, could be expanded to use rp so that in legacy user agents the readings are in parentheses:

... 
<ruby>
 漢 <rp>(</rp><rt>かん</rt><rp>)</rp>
 字 <rp>(</rp><rt>じ</rt><rp>)</rp>
</ruby>
...

In conforming user agents the rendering would be as above, but in user agents that do not support ruby, the rendering would be:

... 漢 (かん) 字 (じ) ...

4.6.25 Usage summary

We need to summarize the various elements, in particular to distinguish b/i/em/strong/var/q/mark/cite.

4.6.26 Footnotes

HTML does not have a dedicated mechanism for marking up footnotes. Here are the recommended alternatives.

For short inline annotations, the title attribute should be used.

In this example, two parts of a dialog are annotated.

<dialog>
 <dt>Customer
 <dd>Hello! I wish to register a complaint. Hello. Miss?
 <dt>Shopkeeper
 <dd><span title="Colloquial pronunciation of 'What do you'"
 >Watcha</span> mean, miss?
 <dt>Customer
 <dd>Uh, I'm sorry, I have a cold. I wish to make a complaint.
 <dt>Shopkeeper
 <dd>Sorry, <span title="This is, of course, a lie.">we're
 closing for lunch</span>.
</dialog>

For longer annotations, the a element should be used, pointing to an element later in the document. The convention is that the contents of the link be a number in square brackets.

In this example, a footnote in the dialog links to a paragraph below the dialog. The paragraph then reciprocally links back to the dialog, allowing the user to return to the location of the footnote.

<dialog>
 <dt>Announcer
 <dd>Number 16: The <i>hand</i>.
 <dt>Interviewer
 <dd>Good evening. I have with me in the studio tonight Mr
 Norman St John Polevaulter, who for the past few years has
 been contradicting people. Mr Polevaulter, why <em>do</em>
 you contradict people?
 <dt>Norman
 <dd>I don't. <a href="#fn1" id="r1">[1]</a>
 <dt>Interviewer
 <dd>You told me you did!
</dialog>
<section>
 <p id="fn1"><a href="#r1">[1]</a> This is, naturally, a lie,
 but paradoxically if it were true he could not say so without
 contradicting the interviewer and thus making it false.</p>
</section>

For side notes, longer annotations that apply to entire sections of the text rather than just specific words or sentences, the aside element should be used.

In this example, a sidebar is given after a dialog, giving some context to the dialog.

<dialog>
 <dt>Customer
 <dd>I will not buy this record, it is scratched.
 <dt>Shopkeeper
 <dd>I'm sorry?
 <dt>Customer
 <dd>I will not buy this record, it is scratched.
 <dt>Shopkeeper
 <dd>No no no, this's'a tobacconist's.
</dialog>
<aside>
 <p>In 1970, the British Empire lay in ruins, and foreign
 nationalists frequented the streets — many of them Hungarians
 (not the streets — the foreign nationals). Sadly, Alexander
 Yalt has been publishing incompetently-written phrase books.
</aside>

4.7 Edits

The ins and del elements represent edits to the document.

4.7.1 The ins element

Categories
Flow content.
When the element only contains phrasing content: phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Transparent.
Content attributes:
Global attributes
cite
datetime
DOM interface:
Uses the HTMLModElement interface.

The ins element represents an addition to the document.

The following represents the addition of a single paragraph:

<aside>
 <ins>
  <p> I like fruit. </p>
 </ins>
</aside>

As does this, because everything in the aside element here counts as phrasing content and therefore there is just one paragraph:

<aside>
 <ins>
  Apples are <em>tasty</em>.
 </ins>
 <ins>
  So are pears.
 </ins>
</aside>

ins elements should not cross implied paragraph boundaries.

The following example represents the addition of two paragraphs, the second of which was inserted in two parts. The first ins element in this example thus crosses a paragraph boundary, which is considered poor form.

<aside>
 <ins datetime="2005-03-16T00:00Z">
  <p> I like fruit. </p>
  Apples are <em>tasty</em>.
 </ins>
 <ins datetime="2007-12-19T00:00Z">
  So are pears.
 </ins>
</aside>

Here is a better way of marking this up. It uses more elements, but none of the elements cross implied paragraph boundaries.

<aside>
 <ins datetime="2005-03-16T00:00Z">
  <p> I like fruit. </p>
 </ins>
 <ins datetime="2005-03-16T00:00Z">
  Apples are <em>tasty</em>.
 </ins>
 <ins datetime="2007-12-19T00:00Z">
  So are pears.
 </ins>
</aside>

4.7.2 The del element

Categories
Flow content.
When the element only contains phrasing content: phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Transparent.
Content attributes:
Global attributes
cite
datetime
DOM interface:
Uses the HTMLModElement interface.

The del element represents a removal from the document.

del elements should not cross implied paragraph boundaries.

4.7.3 Attributes common to ins and del elements

The cite attribute may be used to specify the address of a document that explains the change. When that document is long, for instance the minutes of a meeting, authors are encouraged to include a fragment identifier pointing to the specific part of that document that discusses the change.

If the cite attribute is present, it must be a valid URL that explains the change. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. User agents should allow users to follow such citation links.

The datetime attribute may be used to specify the time and date of the change.

If present, the datetime attribute must be a valid global date and time string value.

User agents must parse the datetime attribute according to the parse a global date and time string algorithm. If that doesn't return a time, then the modification has no associated timestamp (the value is non-conforming; it is not a valid global date and time string). Otherwise, the modification is marked as having been made at the given datetime. User agents should use the associated time-zone information to determine which time zone to present the given datetime in.

The ins and del elements must implement the HTMLModElement interface:

interface HTMLModElement : HTMLElement {
           attribute DOMString cite;
           attribute DOMString dateTime;
};

The cite DOM attribute must reflect the element's cite content attribute. The dateTime DOM attribute must reflect the element's datetime content attribute.

4.7.4 Edits and paragraphs

Since the ins and del elements do not affect paragraphing, it is possible, in some cases where paragraphs are implied (without explicit p elements), for an ins or del element to span both an entire paragraph or other non-phrasing content elements and part of another paragraph.

For example:

<section>
 <ins>
  <p>
   This is a paragraph that was inserted.
  </p>
  This is another paragraph whose first sentence was inserted
  at the same time as the paragraph above.
 </ins>
 This is a second sentence, which was there all along.
</section>

By only wrapping some paragraphs in p elements, one can even get the end of one paragraph, a whole second paragraph, and the start of a third paragraph to be covered by the same ins or del element (though this is very confusing, and not considered good practice):

<section>
 This is the first paragraph. <ins>This sentence was
 inserted.
 <p>This second paragraph was inserted.</p>
 This sentence was inserted too.</ins> This is the
 third paragraph in this example.
</section>

However, due to the way implied paragraphs are defined, it is not possible to mark up the end of one paragraph and the start of the very next one using the same ins or del element. You instead have to use one (or two) p element(s) and two ins or del elements:

For example:

<section>
 <p>This is the first paragraph. <del>This sentence was
 deleted.</del></p>
 <p><del>This sentence was deleted too.</del> That
 sentence needed a separate &lt;del&gt; element.</p>
</section>

Partly because of the confusion described above, authors are strongly recommended to always mark up all paragraphs with the p element, and to not have any ins or del elements that cross across any implied paragraphs.

4.7.5 Edits and lists

The content models of the ol and ul elements do not allow ins and del elements as children. Lists always represent all their items, including items that would otherwise have been marked as deleted.

To indicate that an item is inserted or deleted, an ins or del element can be wrapped around the contents of the li element. To indicate that an item has been replaced by another, a single li element can have one or more del elements followed by one or more ins elements.

In the following example, a list that started empty had items added and removed from it over time. The bits in the example that have been emphasized show the parts that are the "current" state of the list. The list item numbers don't take into account the edits, though.

<h1>Stop-ship bugs</h1>
<ol>
 <li><ins datetime="2008-02-12T15:20Z">Bug 225:
 Rain detector doesn't work in snow</ins></li>
 <li><del datetime="2008-03-01T20:22Z"><ins datetime="2008-02-14T12:02Z">Bug 228:
 Water buffer overflows in April</ins></del></li>
 <li><ins datetime="2008-02-16T13:50Z">Bug 230:
 Water heater doesn't use renewable fuels</ins></li>
 <li><del datetime="2008-02-20T21:15Z"><ins datetime="2008-02-16T14:25Z">Bug 232:
 Carbon dioxide emissions detected after startup</ins></del></li>
</ol>

In the following example, a list that started with just fruit was replaced by a list with just colors.

<h1>List of <del>fruits</del><ins>colors</ins></h1>
<ul>
 <li><del>Lime</del><ins>Green</ins></li>
 <li><del>Apple</del></li>
 <li>Orange</li>
 <li><del>Pear</del></li>
 <li><ins>Teal</ins></li>
 <li><del>Lemon</del><ins>Yellow</ins></li>
 <li>Olive</li>
 <li><ins>Purple</ins>
</ul>

4.8 Embedded content

4.8.1 The figure element

Categories
Flow content.
Sectioning root.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Either: one legend element followed by flow content.
Or: Flow content followed by one legend element.
Or: Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The figure element represents some flow content, optionally with a caption, which can be moved away from the main flow of the document without affecting the document's meaning.

The element can thus be used to annotate illustrations, diagrams, photos, code listings, etc, that are referred to from the main content of the document, but that could, without affecting the flow of the document, be moved away from that primary content, e.g. to the side of the page, to dedicated pages, or to an appendix.

The first legend element child of the element, if any, represents the caption of the figure element's contents. If there is no child legend element, then there is no caption.

The remainder of the element's contents, if any, represents the content.

This example shows the figure element to mark up a code listing.

<p>In <a href="#l4">listing 4</a> we see the primary core interface
API declaration.</p>
<figure id="l4">
 <legend>Listing 4. The primary core interface API declaration.</legend>
 <pre><code>interface PrimaryCore {
  boolean verifyDataLine();
  void sendData(in sequence&lt;byte> data);
  void initSelfDestruct();
}</code></pre>
</figure>
<p>The API is designed to use UTF-8.</p>

Here we see a figure element to mark up a photo.

<figure>
 <img src="bubbles-work.jpeg"
      alt="Bubbles, sitting in his office chair, works on his
           latest project intently.">
 <legend>Bubbles at work</legend>
</figure>

In this example, we see an image that is not a figure, as well as an image and a video that are.

<h2>Malinko's comics</h2>

<p>This case centered on some sort of "intellectual property"
infringement related to a comic (see Exhibit A). The suit started
after a trailer ending with these words:</p>

<img src="promblem-packed-action.png" alt="ROUGH COPY! Promblem-Packed Action!">

<p>...was aired. A lawyer, armed with a Bigger Notebook, launched a
preemptive strike using snowballs. A complete copy of the trailer is
included with Exhibit B.</p>

<figure>
 <img src="ex-a.png" alt="Two squiggles on a dirty piece of paper.">
 <legend>Exhibit A. The alleged <cite>rough copy</cite> comic.</legend>
</figure>

<figure>
 <video src="ex-b.mov"></video>
 <legend>Exhibit B. The <code>Rough Copy</cite> trailer.</legend>
</figure>

<p>The case was resolved out of court.</p>

Here, a part of a poem is marked up using figure.

<figure>
 <p>'Twas brillig, and the slithy toves<br>
Did gyre and gimble in the wabe;<br>
All mimsy were the borogoves,<br>
And the mome raths outgrabe.</p>
 <legend><cite>Jabberwocky</cite> (first verse). Lewis Carroll, 1832-98</legend>
</figure>

In this example, which could be part of a much larger work discussing a castle, the figure has three images in it.

<figure>
 <img src="castle1423.jpeg" title="Etching. Anonymous, ca. 1423."
      alt="The castle has one tower, and a tall wall around it.">
 <img src="castle1858.jpeg" title="Oil-based paint on canvas. Maria Towle, 1858."
      alt="The castle now has two towers and two walls.">
 <img src="castle1999.jpeg" title="Film photograph. Peter Jankle, 1999."
      alt="The castle lies in ruins, the original tower all that remains in one piece.">
 <legend>The castle through the ages: 1423, 1858, and 1999 respectively.</legend>
</figure>

4.8.2 The img element

Categories
Flow content.
Phrasing content.
Embedded content.
If the element has an usemap attribute: Interactive content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Empty.
Content attributes:
Global attributes
alt
src
usemap
ismap
width
height
DOM interface:
[NamedConstructor=Image(),
 NamedConstructor=Image(in unsigned long width),
 NamedConstructor=Image(in unsigned long width, in unsigned long height)]
interface HTMLImageElement : HTMLElement {
           attribute DOMString alt;
           attribute DOMString src;
           attribute DOMString useMap;
           attribute boolean isMap;
           attribute unsigned long width;
           attribute unsigned long height;
  readonly attribute boolean complete;
};

An img element represents an image.

The image given by the src attribute is the embedded content, and the value of the alt attribute is the img element's fallback content.

The src attribute must be present, and must contain a valid URL referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted. If the base URI of the element is the same as the document's address, then the src attribute's value must not be the empty string.

Images can thus be static bitmaps (e.g. PNGs, GIFs, JPEGs), single-page vector documents (single-page PDFs, XML files with an SVG root element), animated bitmaps (APNGs, animated GIFs), animated vector graphics (XML files with an SVG root element that use declarative SMIL animation), and so forth. However, this also precludes SVG files with script, multipage PDF files, interactive MNG files, HTML documents, plain text documents, and so forth.

The requirements on the alt attribute's value are described in the next section.

There has been some suggestion that the longdesc attribute from HTML4 should be included. This has been considered and rejected in the past, but if new evidence is found showing the attribute to actually help users rather than harm them, it may be reconsidered.

The img must not be used as a layout tool. In particular, img elements should not be used to display transparent images, as they rarely convey meaning and rarely add anything useful to the document.


Unless the user agent cannot support images, or its support for images has been disabled, or the user agent only fetches elements on demand, or the element's src attribute has a value that is an ignored self-reference, then, when an img is created with a src attribute, and whenever the src attribute is set subsequently, the user agent must resolve the value of that attribute, relative to the element, and if that is successful must then fetch that resource.

The src attribute's value is an ignored self-reference if its value is the empty string, and the base URI of the element is the same as the document's address.

Fetching the image must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined below) has been run.

This, unfortunately, can be used to perform a rudimentary port scan of the user's local network (especially in conjunction with scripting, though scripting isn't actually necessary to carry out such an attack). User agents may implement cross-origin access control policies that mitigate this attack.

If the image's type is a supported image type, and the image is a valid image of that type, then the image is said to be available (this affects exactly what the element represents, as defined below). This can be true even before the image is completely downloaded, if the user agent supports incremental rendering of images; in such cases, each task that is queued by the networking task source while the image is being fetched must update the presentation of the image appropriately.

If the image was not fetched (e.g. because the UA's image support is disabled, or because the src attribute's value is an ignored self-reference), or if the conditions in the previous paragraph are not met, then the image is not available.

An image might be available in one view but not another. For instance, a Document could be rendered by a screen reader providing a speech synthesis view of the output of a Web browser using the screen media. In this case, the image would be available in the Web browser's screen view, but not available in the screen reader's view.

Whether the image is fetched successfully or not (e.g. whether the response code was a 2xx code or equivalent) must be ignored when determining the image's type and whether it is a valid image.

This allows servers to return images with error responses, and have them displayed.

The user agents should apply the image sniffing rules to determine the type of the image, with the image's associated Content-Type headers giving the official type. If these rules are not applied, then the type of the image must be the type given by the image's associated Content-Type headers.

User agents must not support non-image resources with the img element (e.g. XML files whose root element is an HTML element). User agents must not run executable code (e.g. scripts) embedded in the image resource. User agents must only display the first page of a multipage resource (e.g. a PDF file). User agents must not allow the resource to act in an interactive fashion, but should honor any animation in the resource.

This specification does not specify which image types are to be supported.

The task that is queued by the networking task source once the resource has been fetched, must, if the download was successful and the image is available, queue a task to fire a simple event called load at the img element (this happens after complete starts returning true); and otherwise, if the fetching process fails without a response from the remote server, or completes but the image is not a valid or supported image, queue a task to fire a simple event called error on the img element.

The task source for these tasks is the DOM manipulation task source.


What an img element represents depends on the src attribute and the alt attribute.

If the src attribute is set and the alt attribute is set to the empty string

The image is either decorative or supplemental to the rest of the content, redundant with some other information in the document.

If the image is available and the user agent is configured to display that image, then the element represents the image specified by the src attribute.

Otherwise, the element represents nothing, and may be omitted completely from the rendering. User agents may provide the user with a notification that an image is present but has been omitted from the rendering.

If the src attribute is set and the alt attribute is set to a value that isn't empty

The image is a key part of the content; the alt attribute gives a textual equivalent or replacement for the image.

If the image is available and the user agent is configured to display that image, then the element represents the image specified by the src attribute.

Otherwise, the element represents the text given by the alt attribute. User agents may provide the user with a notification that an image is present but has been omitted from the rendering.

If the src attribute is set and the alt attribute is not

The image might be a key part of the content, and there is no textual equivalent of the image available.

In a conforming document, the absence of the alt attribute indicates that the image is a key part of the content but that a textual replacement for the image was not available when the image was generated.

If the image is available, the element represents the image specified by the src attribute.

If the image is not available or if the user agent is not configured to display the image, then the user agent should display some sort of indicator that there is an image that is not being rendered, and may, if requested by the user, or if so configured, or when required to provide contextual information in response to navigation, provide caption information for the image, derived as follows:

  1. If the image has a title attribute whose value is not the empty string, then the value of that attribute is the caption information; abort these steps.

  2. If the image is the child of a figure element that has a child legend element, then the contents of the first such legend element are the caption information; abort these steps.

  3. Run the algorithm to create the outline for the document.

  4. If the img element did not end up associated with a heading in the outline, or if there are any other images that are lacking an alt attribute and that are associated with the same heading in the outline as the img element in question, then there is no caption information; abort these steps.

  5. The caption information is the heading with which the image is associated according to the outline.

If the src attribute is not set and either the alt attribute is set to the empty string or the alt attribute is not set at all

The element represents nothing.

Otherwise

The element represents the text given by the alt attribute.

The alt attribute does not represent advisory information. User agents must not present the contents of the alt attribute in the same way as content of the title attribute.

User agents may always provide the user with the option to display any image, or to prevent any image from being displayed. User agents may also apply image analysis heuristics to help the user make sense of the image when the user is unable to make direct use of the image, e.g. due to a visual disability or because they are using a text terminal with no graphics capabilities.

The contents of img elements, if any, are ignored for the purposes of rendering.


The usemap attribute, if present, can indicate that the image has an associated image map.

The ismap attribute, when used on an element that is a descendant of an a element with an href attribute, indicates by its presence that the element provides access to a server-side image map. This affects how events are handled on the corresponding a element.

The ismap attribute is a boolean attribute. The attribute must not be specified on an element that does not have an ancestor a element with an href attribute.

The img element supports dimension attributes.

The DOM attributes alt, src, useMap, and isMap each must reflect the respective content attributes of the same name.

image . width [ = value ]
image . height [ = value ]

These attributes return the actual rendered dimensions of the image, or zero if the dimensions are not known.

They can be set, to change the corresponding content attributes.

image . complete

Returns true if the image has been downloaded, decoded, and found to be valid; otherwise, returns false.

image = new Image( [ width [, height ] ] )

Returns a new img element, with the width and height attributes set to the values passed in the relevant arguments, if applicable.

The DOM attributes width and height must return the rendered width and height of the image, in CSS pixels, if the image is being rendered, and is being rendered to a visual medium; or else the intrinsic width and height of the image, in CSS pixels, if the image is available but not being rendered to a visual medium; or else 0, if the image is not available or its dimensions are not known. [CSS21]

On setting, they must act as if they reflected the respective content attributes of the same name.

The DOM attribute complete must return true if the user agent has fetched the image specified in the src attribute, and it is a valid image, even if the final task queued by the networking task source for the fetching of the image resource has not yet been processed. Otherwise, the attribute must return false.

The value of complete can thus change while a script is executing.

Three constructors are provided for creating HTMLImageElement objects (in addition to the factory methods from DOM Core such as createElement()): Image(), Image(width), and Image(width, height). When invoked as constructors, these must return a new HTMLImageElement object (a new img element). If the width argument is present, the new object's width content attribute must be set to width. If the height argument is also present, the new object's height content attribute must be set to height.

A single image can have different appropriate alternative text depending on the context.

In each of the following cases, the same image is used, yet the alt text is different each time. The image is the coat of arms of the Canton Geneva in Switzerland.

Here it is used as a supplementary icon:

<p>I lived in <img src="carouge.svg" alt=""> Carouge.</p>

Here it is used as an icon representing the town:

<p>Home town: <img src="carouge.svg" alt="Carouge"></p>

Here it is used as part of a text on the town:

<p>Carouge has a coat of arms.</p>
<p><img src="carouge.svg" alt="The coat of arms depicts a lion, sitting in front of a tree."></p>
<p>It is used as decoration all over the town.</p>

Here it is used as a way to support a similar text where the description is given as well as, instead of as an alternative to, the image:

<p>Carouge has a coat of arms.</p>
<p><img src="carouge.svg" alt=""></p>
<p>The coat of arms depicts a lion, sitting in front of a tree.
It is used as decoration all over the town.</p>

Here it is used as part of a story:

<p>He picked up the folder and a piece of paper fell out.</p>
<p><img src="carouge.svg" alt="Shaped like a shield, the paper had a
red background, a green tree, and a yellow lion with its tongue
hanging out and whose tail was shaped like an S."></p>
<p>He stared at the folder. S! The answer he had been looking for all
this time was simply the letter S! How had he not seen that before? It all
came together now. The phone call where Hector had referred to a lion's tail,
the time Marco had stuck his tongue out...</p>

Here it is not known at the time of publication what the image will be, only that it will be a coat of arms of some kind, and thus no replacement text can be provided, and instead only a brief caption for the image is provided, in the title attribute:

<p>The last user to have uploaded a coat of arms uploaded this one:</p>
<p><img src="last-uploaded-coat-of-arms.cgi" title="User-uploaded coat of arms."></p>

Ideally, the author would find a way to provide real replacement text even in this case, e.g. by asking the previous user. Not providing replacement text makes the document more difficult to use for people who are unable to view images, e.g. blind users, or users or very low-bandwidth connections or who pay by the byte, or users who are forced to use a text-only Web browser.

Here are some more examples showing the same picture used in different contexts, with different appropriate alternate texts each time.

<article>
 <h1>My cats</h1>
 <h2>Fluffy</h2>
 <p>Fluffy is my favorite.</p>
 <img src="fluffy.jpg" alt="She likes playing with a ball of yarn.">
 <p>She's just too cute.</p>
 <h2>Miles</h2>
 <p>My other cat, Miles just eats and sleeps.</p>
</article>
<article>
 <h1>Photography</h1>
 <h2>Shooting moving targets indoors</h2>
 <p>The trick here is to know how to anticipate; to know at what speed and
 what distance the subject will pass by.</p>
 <img src="fluffy.jpg" alt="A cat flying by, chasing a ball of yarn, can be
 photographed quite nicely using this technique.">
 <h2>Nature by night</h2>
 <p>To achieve this, you'll need either an extremely sensitive film, or
 immense flash lights.</p>
</article>
<article>
 <h1>About me</h1>
 <h2>My pets</h2>
 <p>I've got a cat named Fluffy and a dog named Miles.</p>
 <img src="fluffy.jpg" alt="Fluffy, my cat, tends to keep itself busy.">
 <p>My dog Miles and I like go on long walks together.</p>
 <h2>music</h2>
 <p>After our walks, having emptied my mind, I like listening to Bach.</p>
</article>
<article>
 <h1>Fluffy and the Yarn</h1>
 <p>Fluffy was a cat who liked to play with yarn. He also liked to jump.</p>
 <aside><img src="fluffy.jpg" alt="" title="Fluffy"></aside>
 <p>He would play in the morning, he would play in the evening.</p>
</article>
4.8.2.1 Requirements for providing text to act as an alternative for images

The requirements for the alt attribute depend on what the image is intended to represent, as described in the following sections.

When an a element that is a hyperlink, or a button element, has no textual content but contains one or more images, the alt attributes must contain text that together convey the purpose of the link or button.

In this example, a user is asked to pick his preferred color from a list of three. Each color is given by an image, but for users who have configured their user agent not to display images, the color names are used instead:

<h1>Pick your color</h1>
<ul>
 <li><a href="green.html"><img src="green.jpeg" alt="Green"></a></li>
 <li><a href="blue.html"><img src="blue.jpeg" alt="Blue"></a></li>
 <li><a href="red.html"><img src="red.jpeg" alt="Red"></a></li>
</ul>

In this example, each button has a set of images to indicate the kind of color output desired by the user. The first image is used in each case to give the alternative text.

<button name="rgb"><img src="red" alt="RGB"><img src="green" alt=""><img src="blue" alt=""></button>
<button name="cmyk"><img src="cyan" alt="CMYK"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></button>

Since each image represents one part of the text, it could also be written like this:

<button name="rgb"><img src="red" alt="R"><img src="green" alt="G"><img src="blue" alt="B"></button>
<button name="cmyk"><img src="cyan" alt="C"><img src="magenta" alt="M"><img src="yellow" alt="Y"><img src="black" alt="K"></button>

However, with other alternative text, this might not work, and putting all the alternative text into one image in each case might make more sense:

<button name="rgb"><img src="red" alt="sRGB profile"><img src="green" alt=""><img src="blue" alt=""></button>
<button name="cmyk"><img src="cyan" alt="CMYK profile"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></button>
4.8.2.1.2 A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations

Sometimes something can be more clearly stated in graphical form, for example as a flowchart, a diagram, a graph, or a simple map showing directions. In such cases, an image can be given using the img element, but the lesser textual version must still be given, so that users who are unable to view the image (e.g. because they have a very slow connection, or because they are using a text-only browser, or because they are listening to the page being read out by a hands-free automobile voice Web browser, or simply because they are blind) are still able to understand the message being conveyed.

The text must be given in the alt attribute, and must convey the same message as the image specified in the src attribute.

It is important to realize that the alternative text is a replacement for the image, not a description of the image.

In the following example we have a flowchart in image form, with text in the alt attribute rephrasing the flowchart in prose form:

<p>In the common case, the data handled by the tokenization stage
comes from the network, but it can also come from script.</p>
<p><img src="images/parsing-model-overview.png" alt="The network
passes data to the Tokenizer stage, which passes data to the Tree
Construction stage. From there, data goes to both the DOM and to
Script Execution. Script Execution is linked to the DOM, and, using
document.write(), passes data to the Tokenizer."></p>

Here's another example, showing a good solution and a bad solution to the problem of including an image in a description.

First, here's the good solution. This sample shows how the alternative text should just be what you would have put in the prose if the image had never existed.

<!-- This is the correct way to do things. -->
<p>
 You are standing in an open field west of a house.
 <img src="house.jpeg" alt="The house is white, with a boarded front door.">
 There is a small mailbox here.
</p>

Second, here's the bad solution. In this incorrect way of doing things, the alternative text is simply a description of the image, instead of a textual replacement for the image. It's bad because when the image isn't shown, the text doesn't flow as well as in the first example.

<!-- This is the wrong way to do things. -->
<p>
 You are standing in an open field west of a house.
 <img src="house.jpeg" alt="A white house, with a boarded front door.">
 There is a small mailbox here.
</p>

Text such as "Photo of white house with boarded door" would be equally bad alternative text (though it could be suitable for the title attribute or in the legend element of a figure with this image).

4.8.2.1.3 A short phrase or label with an alternative graphical representation: icons, logos

A document can contain information in iconic form. The icon is intended to help users of visual browsers to recognize features at a glance.

In some cases, the icon is supplemental to a text label conveying the same meaning. In those cases, the alt attribute must be present but must be empty.

Here the icons are next to text that conveys the same meaning, so they have an empty alt attribute:

<nav>
 <p><a href="/help/"><img src="/icons/help.png" alt=""> Help</a></p>
 <p><a href="/configure/"><img src="/icons/configuration.png" alt="">
 Configuration Tools</a></p>
</nav>

In other cases, the icon has no text next to it describing what it means; the icon is supposed to be self-explanatory. In those cases, an equivalent textual label must be given in the alt attribute.

Here, posts on a news site are labeled with an icon indicating their topic.

<body>
 <article>
  <header>
   <h1>Ratatouille wins <i>Best Movie of the Year</i> award</h1>
   <p><img src="movies.png" alt="Movies"></p>
  </header>
  <p>Pixar has won yet another <i>Best Movie of the Year</i> award,
  making this its 8th win in the last 12 years.</p>
 </article>
 <article>
  <header>
   <h1>Latest TWiT episode is online</h1>
   <p><img src="podcasts.png" alt="Podcasts"></p>
  </header>
  <p>The latest TWiT episode has been posted, in which we hear
  several tech news stories as well as learning much more about the
  iPhone. This week, the panelists compare how reflective their
  iPhones' Apple logos are.</p>
 </article>
</body>

Many pages include logos, insignia, flags, or emblems, which stand for a particular entity such as a company, organization, project, band, software package, country, or some such.

If the logo is being used to represent the entity, e.g. as a page heading, the alt attribute must contain the name of the entity being represented by the logo. The alt attribute must not contain text like the word "logo", as it is not the fact that it is a logo that is being conveyed, it's the entity itself.

If the logo is being used next to the name of the entity that it represents, then the logo is supplemental, and its alt attribute must instead be empty.

If the logo is merely used as decorative material (as branding, or, for example, as a side image in an article that mentions the entity to which the logo belongs), then the entry below on purely decorative images applies. If the logo is actually being discussed, then it is being used as a phrase or paragraph (the description of the logo) with an alternative graphical representation (the logo itself), and the first entry above applies.

In the following snippets, all four of the above cases are present. First, we see a logo used to represent a company:

<h1><img src="XYZ.gif" alt="The XYZ company"></h1>

Next, we see a paragraph which uses a logo right next to the company name, and so doesn't have any alternative text:

<article>
 <h2>News</h2>
 <p>We have recently been looking at buying the <img src="alpha.gif"
 alt=""> ΑΒΓ company, a small Greek company
 specializing in our type of product.</p>

In this third snippet, we have a logo being used in an aside, as part of the larger article discussing the acquisition:

 <aside><p><img src="alpha-large.gif" alt=""></p></aside>
 <p>The ΑΒΓ company has had a good quarter, and our
 pie chart studies of their accounts suggest a much bigger blue slice
 than its green and orange slices, which is always a good sign.</p>
</article>

Finally, we have an opinion piece talking about a logo, and the logo is therefore described in detail in the alternative text.

<p>Consider for a moment their logo:</p>

<p><img src="/images/logo" alt="It consists of a green circle with a
green question mark centered inside it."></p>

<p>How unoriginal can you get? I mean, oooooh, a question mark, how
<em>revolutionary</em>, how utterly <em>ground-breaking</em>, I'm
sure everyone will rush to adopt those specifications now! They could
at least have tried for some sort of, I don't know, sequence of
rounded squares with varying shades of green and bold white outlines,
at least that would look good on the cover of a blue book.</p>

This example shows how the alternative text should be written such that if the image isn't available, and the text is used instead, the text flows seamlessly into the surrounding text, as if the image had never been there in the first place.

4.8.2.1.4 Text that has been rendered to a graphic for typographical effect

Sometimes, an image just consists of text, and the purpose of the image is not to highlight the actual typographic effects used to render the text, but just to convey the text itself.

In such cases, the alt attribute must be present but must consist of the same text as written in the image itself.

Consider a graphic containing the text "Earth Day", but with the letters all decorated with flowers and plants. If the text is merely being used as a heading, to spice up the page for graphical users, then the correct alternative text is just the same text "Earth Day", and no mention need be made of the decorations:

<h1><img src="earthdayheading.png" alt="Earth Day"></h1>
4.8.2.1.5 A graphical representation of some of the surrounding text

In many cases, the image is actually just supplementary, and its presence merely reinforces the surrounding text. In these cases, the alt attribute must be present but its value must be the empty string.

In general, an image falls into this category if removing the image doesn't make the page any less useful, but including the image makes it a lot easier for users of visual browsers to understand the concept.

A flowchart that repeats the previous paragraph in graphical form:

<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<p><img src="images/parsing-model-overview.png" alt=""></p>

In these cases, it would be wrong to include alternative text that consists of just a caption. If a caption is to be included, then either the title attribute can be used, or the figure and legend elements can be used. In the latter case, the image would in fact be a phrase or paragraph with an alternative graphical representation, and would thus require alternative text.

<!-- Using the title="" attribute -->
<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<p><img src="images/parsing-model-overview.png" alt=""
        title="Flowchart representation of the parsing model."></p>
<!-- Using <figure> and <legend> -->
<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<figure>
 <img src="images/parsing-model-overview.png" alt="The Network leads
 to the Tokenizer, which leads to the Tree Construction. The Tree
 Construction leads to two items. The first is Script Execution, which
 leads via document.write() back to the Tokenizer. The second item
 from which Tree Construction leads is the DOM. The DOM is related to
 the Script Execution.">
 <legend>Flowchart representation of the parsing model.</legend>
</figure>
<!-- This is WRONG. Do not do this. Instead, do what the above examples do. -->
<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<p><img src="images/parsing-model-overview.png"
        alt="Flowchart representation of the parsing model."></p>
<!-- Never put the image's caption in the alt="" attribute! -->

A graph that repeats the previous paragraph in graphical form:

<p>According to a study covering several billion pages,
about 62% of documents on the Web in 2007 triggered the Quirks
rendering mode of Web browsers, about 30% triggered the Almost
Standards mode, and about 9% triggered the Standards mode.</p>
<p><img src="rendering-mode-pie-chart.png" alt=""></p>
4.8.2.1.6 A purely decorative image that doesn't add any information

In general, if an image is decorative but isn't especially page-specific, for example an image that forms part of a site-wide design scheme, the image should be specified in the site's CSS, not in the markup of the document.

However, a decorative image that isn't discussed by the surrounding text still has some relevance can be included in a page using the img element. Such images are decorative, but still form part of the content. In these cases, the alt attribute must be present but its value must be the empty string.

Examples where the image is purely decorative despite being relevant would include things like a photo of the Black Rock City landscape in a blog post about an event at Burning Man, or an image of a painting inspired by a poem, on a page reciting that poem. The following snippet shows an example of the latter case (only the first verse is included in this snippet):

<h1>The Lady of Shalott</h1>
<p><img src="shalott.jpeg" alt=""></p>
<p>On either side the river lie<br>
Long fields of barley and of rye,<br>
That clothe the wold and meet the sky;<br>
And through the field the road run by<br>
To many-tower'd Camelot;<br>
And up and down the people go,<br>
Gazing where the lilies blow<br>
Round an island there below,<br>
The island of Shalott.</p>

When a picture has been sliced into smaller image files that are then displayed together to form the complete picture again, one of the images must have its alt attribute set as per the relevant rules that would be appropriate for the picture as a whole, and then all the remaining images must have their alt attribute set to the empty string.

In the following example, a picture representing a company logo for XYZ Corp has been split into two pieces, the first containing the letters "XYZ" and the second with the word "Corp". The alternative text ("XYZ Corp") is all in the first image.

<h1><img src="logo1.png" alt="XYZ Corp"><img src="logo2.png" alt=""></h1>

In the following example, a rating is shown as three filled stars and two empty stars. While the alternative text could have been "★★★☆☆", the author has instead decided to more helpfully give the rating in the form "3 out of 5". That is the alternative text of the first image, and the rest have blank alternative text.

<p>Rating: <meter max=5 value=3><img src="1" alt="3 out of 5"
  ><img src="1" alt=""><img src="1" alt=""><img src="0" alt=""
  ><img src="0" alt=""></meter></p>

Generally, image maps should be used instead of slicing an image for links.

However, if an image is indeed sliced and any of the components of the sliced picture are the sole contents of links, then one image per link must have alternative text in its alt attribute representing the purpose of the link.

In the following example, a picture representing the flying spaghetti monster emblem, with each of the left noodly appendages and the right noodly appendages in different images, so that the user can pick the left side or the right side in an adventure.

<h1>The Church</h1>
<p>You come across a flying spaghetti monster. Which side of His
Noodliness do you wish to reach out for?</p>
<p><a href="?go=left" ><img src="fsm-left.png"  alt="Left side. "></a
  ><img src="fsm-middle.png" alt=""
  ><a href="?go=right"><img src="fsm-right.png" alt="Right side."></a></p>
4.8.2.1.9 A key part of the content

In some cases, the image is a critical part of the content. This could be the case, for instance, on a page that is part of a photo gallery. The image is the whole point of the page containing it.

How to provide alternative text for an image that is a key part of the content depends on the image's provenance.

The general case

When it is possible for detailed alternative text to be provided, for example if the image is part of a series of screenshots in a magazine review, or part of a comic strip, or is a photograph in a blog entry about that photograph, text that can serve as a substitute for the image must be given as the contents of the alt attribute.

A screenshot in a gallery of screenshots for a new OS, with some alternative text:

<figure>
 <img src="KDE%20Light%20desktop.png"
      alt="The desktop is blue, with icons along the left hand side in
           two columns, reading System, Home, K-Mail, etc. A window is
           open showing that menus wrap to a second line if they
           cannot fit in the window. The window has a list of icons
           along the top, with an address bar below it, a list of
           icons for tabs along the left edge, a status bar on the
           bottom, and two panes in the middle. The desktop has a bar
           at the bottom of the screen with a few buttons, a pager, a
           list of open applications, and a clock.">
 <legend>Screenshot of a KDE desktop.</legend>
</figure>

A graph in a financial report:

<img src="sales.gif"
     title="Sales graph"
     alt="From 1998 to 2005, sales increased by the following percentages
     with each year: 624%, 75%, 138%, 40%, 35%, 9%, 21%">

Note that "sales graph" would be inadequate alternative text for a sales graph. Text that would be a good caption is not generally suitable as replacement text.

Images that defy a complete description

In certain cases, the nature of the image might be such that providing thorough alternative text is impractical. For example, the image could be indistinct, or could be a complex fractal, or could be a detailed topographical map.

In these cases, the alt attribute must contain some suitable alternative text, but it may be somewhat brief.

Sometimes there simply is no text that can do justice to an image. For example, there is little that can be said to usefully describe a Rorschach inkblot test. However, a description, even if brief, is still better than nothing:

<figure>
 <img src="/commons/a/a7/Rorschach1.jpg" alt="A shape with left-right
 symmetry with indistinct edges, with a small gap in the center, two
 larger gaps offset slightly from the center, with two similar gaps
 under them. The outline is wider in the top half than the bottom
 half, with the sides extending upwards higher than the center, and
 the center extending below the sides.">
 <legend>A black outline of the first of the ten cards
 in the Rorschach inkblot test.</legend>
</figure>

Note that the following would be a very bad use of alternative text:

<!-- This example is wrong. Do not copy it. -->
<figure>
 <img src="/commons/a/a7/Rorschach1.jpg" alt="A black outline
 of the first of the ten cards in the Rorschach inkblot test.">
 <legend>A black outline of the first of the ten cards
 in the Rorschach inkblot test.</legend>
</figure>

Including the caption in the alternative text like this isn't useful because it effectively duplicates the caption for users who don't have images, taunting them twice yet not helping them any more than if they had only read or heard the caption once.

Another example of an image that defies full description is a fractal, which, by definition, is infinite in complexity.

The following example shows one possible way of providing alternative text for the full view of an image of the Mandelbrot set.

<img src="ms1.jpeg" alt="The Mandelbrot set appears as a cardioid with
its cusp on the real axis in the positive direction, with a smaller
bulb aligned along the same center line, touching it in the negative
direction, and with these two shapes being surrounded by smaller bulbs
of various sizes.">
Images whose contents are not known

In some unfortunate cases, there might be no alternative text available at all, either because the image is obtained in some automated fashion without any associated alternative text (e.g. a Webcam), or because the page is being generated by a script using user-provided images where the user did not provide suitable or usable alternative text (e.g. photograph sharing sites), or because the author does not himself know what the images represent (e.g. a blind photographer sharing an image on his blog).

In such cases, the alt attribute's value may be omitted, but one of the following conditions must be met as well:

Such cases are to be kept to an absolute minimum. If there is even the slightest possibility of the author having the ability to provide real alternative text, then it would not be acceptable to omit the alt attribute.

A photo on a photo-sharing site, if the site received the image with no metadata other than the caption:

<figure>
 <img src="1100670787_6a7c664aef.jpg">
 <legend>Bubbles traveled everywhere with us.</legend>
</figure>

It could also be marked up like this:

<article>
 <h1>Bubbles traveled everywhere with us.</h1>
 <img src="1100670787_6a7c664aef.jpg">
</article>

In either case, though, it would be better if a detailed description of the important parts of the image obtained from the user and included on the page.

A blind user's blog in which a photo taken by the user is shown. Initially, the user might not have any idea what the photo he took shows:

<article>
 <h1>I took a photo</h1>
 <p>I went out today and took a photo!</p>
 <figure>
  <img src="photo2.jpeg">
  <legend>A photograph taken blindly from my front porch.</legend>
 </figure>
</article>

Eventually though, the user might obtain a description of the image from his friends and could then include alternative text:

<article>
 <h1>I took a photo</h1>
 <p>I went out today and took a photo!</p>
 <figure>
  <img src="photo2.jpeg" alt="The photograph shows my hummingbird
  feeder hanging from the edge of my roof. It is half full, but there
  are no birds around. In the background, out-of-focus trees fill the
  shot. The feeder is made of wood with a metal grate, and it contains
  peanuts. The edge of the roof is wooden too, and is painted white
  with light blue streaks.">
  <legend>A photograph taken blindly from my front porch.</legend>
 </figure>
</article>

Sometimes the entire point of the image is that a textual description is not available, and the user is to provide the description. For instance, the point of a CAPTCHA image is to see if the user can literally read the graphic. Here is one way to mark up a CAPTCHA (note the title attribute):

<p><label>What does this image say?
<img src="captcha.cgi?id=8934" title="CAPTCHA">
<input type=text name=captcha></label>
(If you cannot see the image, you can use an <a
href="?audio">audio</a> test instead.)</p>

Another example would be software that displays images and asks for alternative text precisely for the purpose of then writing a page with correct alternative text. Such a page could have a table of images, like this:

<table>
 <thead>
  <tr> <th> Image <th> Description
 <tbody>
  <tr>
   <td> <img src="2421.png" title="Image 640 by 100, filename 'banner.gif'">
   <td> <input name="alt2421">
  <tr>
   <td> <img src="2422.png" title="Image 200 by 480, filename 'ad3.gif'">
   <td> <input name="alt2422">
</table>

Notice that even in this example, as much useful information as possible is still included in the title attribute.

Since some users cannot use images at all (e.g. because they have a very slow connection, or because they are using a text-only browser, or because they are listening to the page being read out by a hands-free automobile voice Web browser, or simply because they are blind), the alt attribute is only allowed to be omitted rather than being provided with replacement text when no alternative text is available and none can be made available, as in the above examples. Lack of effort from the part of the author is not an acceptable reason for omitting the alt attribute.

4.8.2.1.10 An image not intended for the user

Generally authors should avoid using img elements for purposes other than showing images.

If an img element is being used for purposes other than showing an image, e.g. as part of a service to count page views, then the alt attribute must be the empty string.

In such cases, the width and height attributes should both be set to zero.

4.8.2.1.11 An image in an e-mail or private document intended for a specific person who is known to be able to view images

This section does not apply to documents that are publicly accessible, or whose target audience is not necessarily personally known to the author, such as documents on a Web site, e-mails sent to public mailing lists, or software documentation.

When an image is included in a private communication (such as an HTML e-mail) aimed at a specific person who is known to be able to view images, the alt attribute may be omitted. However, even in such cases it is strongly recommended that alternative text be included (as appropriate according to the kind of image involved, as described in the above entries), so that the e-mail is still usable should the user use a mail client that does not support images, or should the document be forwarded on to other users whose abilities might not include easily seeing images.

4.8.2.1.12 General guidelines

The most general rule for writing alternative text is that the intent is that replacing every image with the text of its alt attribute not change the meaning of the page.

So, in general, alternative text can be written by considering what one would have written had one not been able to include the image.

A corollary to this is that the alt attribute's value should never contain text that could be considered the image's caption, title, or legend. It is supposed to contain replacement text that could be used by users instead of the image; it is not meant to supplement the image. The title attribute can be used for supplemental information.

One way to think of alternative text is to think about how you would read the page containing the image to someone over the phone, without mentioning that there is an image present. Whatever you say instead of the image is typically a good start for writing the alternative text.

4.8.2.1.13 Guidance for markup generators

Markup generators (such as WYSIWYG authoring tools) should, wherever possible, obtain alternative text from their users. However, it is recognized that in many cases, this will not be possible.

For images that are the sole contents of links, markup generators should examine the link target to determine the title of the target, or the URL of the target, and use information obtained in this manner as the alternative text.

As a last resort, implementors should either set the alt attribute to the empty string, under the assumption that the image is a purely decorative image that doesn't add any information but is still specific to the surrounding content, or omit the alt attribute altogether, under the assumption that the image is a key part of the content.

Markup generators should generally avoid using the image's own file name as the alternative text.

4.8.2.1.14 Guidance for conformance checkers

Conformance checkers must report the lack of an alt attribute as an error unless the conditions listed above for images whose contents are not known or they have been configured to assume that the document is an e-mail or document intended for a specific person who is known to be able to view images.

4.8.3 The iframe element

Categories
Flow content.
Phrasing content.
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Text that conforms to the requirements given in the prose.
Content attributes:
Global attributes
src
name
sandbox
seamless
width
height
DOM interface:
interface HTMLIFrameElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString name;
           attribute DOMString sandbox;
           attribute boolean seamless;
           attribute DOMString width;
           attribute DOMString height;
};

Objects implementing the HTMLIFrameElement interface must also implement the EmbeddingElement interface defined in the Window Object specification. [WINDOW]

The iframe element represents a nested browsing context.

The src attribute gives the address of a page that the nested browsing context is to contain. The attribute, if present, must be a valid URL. When the browsing context is created, if the attribute is present, the user agent must resolve the value of that attribute, relative to the element, and if that is successful, must then navigate the element's browsing context to the resulting absolute URL, with replacement enabled, and with the iframe element's document's browsing context as the source browsing context. If the user navigates away from this page, the iframe's corresponding WindowProxy object will proxy new Window objects for new Document objects, but the src attribute will not change.

Whenever the src attribute is set, the user agent must resolve the value of that attribute, relative to the element, and if that is successful, the nested browsing context must be navigated to the resulting absolute URL, with the iframe element's document's browsing context as the source browsing context.

If the src attribute is not set when the element is created, or if its value cannot be resolved, the browsing context will remain at the initial about:blank page.

The name attribute, if present, must be a valid browsing context name. The given value is used to name the nested browsing context. When the browsing context is created, if the attribute is present, the browsing context name must be set to the value of this attribute; otherwise, the browsing context name must be set to the empty string.

Whenever the name attribute is set, the nested browsing context's name must be changed to the new value. If the attribute is removed, the browsing context name must be set to the empty string.

When content loads in an iframe, after any load events are fired within the content itself, the user agent must fire a simple event called load at the iframe element. When content fails to load (e.g. due to a network error), then the user agent must fire a simple event called error at the element instead.

When there is an active parser in the iframe, and when anything in the iframe is delaying the load event of the iframe's browsing context's active document, the iframe must delay the load event of its document.

If, during the handling of the load event, the browsing context in the iframe is again navigated, that will further delay the load event.


The sandbox attribute, when specified, enables a set of extra restrictions on any content hosted by the iframe. Its value must be an unordered set of unique space-separated tokens. The allowed values are allow-same-origin, allow-forms, and allow-scripts. When the attribute is set, the content is treated as being from a unique origin, forms and scripts are disabled, links are prevented from targeting other browsing contexts, and plugins are disabled. The allow-same-origin token allows the content to be treated as being from the same origin instead of forcing it into a unique origin, and the allow-forms and allow-scripts tokens re-enable forms and scripts respectively (though scripts are still prevented from creating popups).

While the sandbox attribute is specified, the iframe element's nested browsing context, and all the browsing contexts nested within it (either directly or indirectly through other nested browsing contexts) must have the following flags set:

The sandboxed navigation browsing context flag

This flag prevents content from navigating browsing contexts other than the sandboxed browsing context itself (or browsing contexts further nested inside it).

This flag also prevents content from creating new auxiliary browsing contexts, e.g. using the target attribute or the window.open() method.

The sandboxed plugins browsing context flag

This flag prevents content from instantiating plugins, whether using the embed element, the object element, the applet element, or through navigation of a nested browsing context.

The sandboxed origin browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-same-origin keyword set

This flag forces content into a unique origin for the purposes of the same-origin policy.

This flag also prevents script from reading the document.cookie DOM attribute.

The allow-same-origin attribute is intended for two cases.

First, it can be used to allow content from the same site to be sandboxed to disable scripting, while still allowing access to the DOM of the sandboxed content.

Second, it can be used to embed content from a third-party site, sandboxed to prevent that site from opening popup windows, etc, without preventing the embedded page from communicating back to its originating site, using the database APIs to store data, etc.

This flag only takes effect when the nested browsing context of the iframe is navigated.

The sandboxed forms browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-forms keyword set

This flag blocks form submission.

The sandboxed scripts browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-scripts keyword set

This flag blocks script execution.

If the sandbox attribute is dynamically added after the iframe has loaded a page, scripts already compiled by that page (whether in script elements, or in event handler attributes, or elsewhere) will continue to run. Only new scripts will be prevented from executing by this flag.

These flags must not be set unless the conditions listed above define them as being set.

In this example, some completely-unknown, potentially hostile, user-provided HTML content is embedded in a page. Because it is sandboxed, it is treated by the user agent as being from a unique origin, despite the content being served from the same site. Thus it is affected by all the normal cross-site restrictions. In addition, the embedded page has scripting disabled, plugins disabled, forms disabled, and it cannot navigate any frames or windows other than itself (or any frames or windows it itself embeds).

<p>We're not scared of you! Here is your content, unedited:</p>
<iframe sandbox src="getusercontent.cgi?id=12193"></iframe>

Note that cookies are still sent to the server in the getusercontent.cgi request, though they are not visible in the document.cookie DOM attribute.

In this example, a gadget from another site is embedded. The gadget has scripting and forms enabled, and the origin sandbox restrictions are lifted, allowing the gadget to communicate with its originating server. The sandbox is still useful, however, as it disables plugins and popups, thus reducing the risk of the user being exposed to malware and other annoyances.

<iframe sandbox="allow-same-origin allow-forms allow-scripts"
        src="http://maps.example.com/embedded.html"></iframe>

The seamless attribute is a boolean attribute. When specified, it indicates that the iframe element's browsing context is to be rendered in a manner that makes it appear to be part of the containing document (seamlessly included in the parent document). Specifically, when the attribute is set on an element and while the browsing context's active document has the same origin as the iframe element's document, or the browsing context's active document's address has the same origin as the iframe element's document, the following requirements apply:

If the attribute is not specified, or if the origin conditions listed above are not met, then the user agent should render the nested browsing context in a manner that is clearly distinguishable as a separate browsing context, and the seamless browsing context flag must be set to false for that browsing context.

It is important that user agents recheck the above conditions whenever the active document of the nested browsing context of the iframe changes, such that the seamless browsing context flag gets unset if the nested browsing context is navigated to another origin.

The attribute can be set or removed dynamically, with the rendering updating in tandem.

In this example, the site's navigation is embedded using a client-side include using an iframe. Any links in the iframe will, in new user agents, be automatically opened in the iframe's parent browsing context; for legacy user agents, the site could also include a base element with a target attribute with the value _parent. Similarly, in new user agents the styles of the parent page will be automatically applied to the contents of the frame, but to support legacy user agents authors might wish to include the styles explicitly.

<nav><iframe seamless src="nav.include.html"></iframe></nav>

The iframe element supports dimension attributes for cases where the embedded content has specific dimensions (e.g. ad units have well-defined dimensions).

An iframe element never has fallback content, as it will always create a nested browsing context, regardless of whether the specified initial contents are successfully used.

Descendants of iframe elements represent nothing. (In legacy user agents that do not support iframe elements, the contents would be parsed as markup that could act as fallback content.)

The content model of iframe elements is text, except that the text must be such that ... anyone have any bright ideas?

The HTML parser treats markup inside iframe elements as text.

The DOM attributes src, name, sandbox, and seamless must reflect the respective content attributes of the same name.

4.8.4 The embed element

Categories
Flow content.
Phrasing content.
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Empty.
Content attributes:
Global attributes
src
type
width
height
Any other attribute that has no namespace (see prose).
DOM interface:
interface HTMLEmbedElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString type;
           attribute DOMString width;
           attribute DOMString height;
};

Depending on the type of content instantiated by the embed element, the node may also support other interfaces.

The embed element represents an integration point for an external (typically non-HTML) application or interactive content.

The src attribute gives the address of the resource being embedded. The attribute, if present, must contain a valid URL.

The type attribute, if present, gives the MIME type of the plugin to instantiate. The value must be a valid MIME type, optionally with parameters. If both the type attribute and the src attribute are present, then the type attribute must specify the same type as the explicit Content-Type metadata of the resource given by the src attribute. [RFC2046]

When the element is created with neither a src attribute nor a type attribute, and when attributes are removed such that neither attribute is present on the element anymore, and when the element has an ancestor object element that is not showing its fallback content, any plugins instantiated for the element must be removed, and the embed element represents nothing.

When the sandboxed plugins browsing context flag is set on the browsing context for which the embed element's document is the active document, then the user agent must render the embed element in a manner that conveys that the plugin was disabled. The user agent may offer the user the option to override the sandbox and instantiate the plugin anyway; if the user invokes such an option, the user agent must act as if the sandboxed plugins browsing context flag was not set for the purposes of this element.

Plugins are disabled in sandboxed browsing contexts because they might not honor the restrictions imposed by the sandbox (e.g. they might allow scripting even when scripting in the sandbox is disabled). User agents should convey the danger of overriding the sandbox to the user if an option to do so is provided.

When the element is created with a src attribute, and whenever the src attribute is subsequently set, and whenever the type attribute is set or removed while the element has a src attribute, if the element is not in a sandboxed browsing context and not a descendant of an object element that is not showing its fallback content, the user agent must resolve the value of the attribute, relative to the element, and if that is successful, should fetch the resulting absolute URL. The task that is queued by the networking task source once the resource has been fetched must find and instantiate an appropriate plugin based on the content's type, and hand that plugin the content of the resource, replacing any previously instantiated plugin for the element.

Fetching the resource must delay the load event of the element's document.

The type of the content being embedded is defined as follows:

  1. If the element has a type attribute, and that attribute's value is a type that a plugin supports, then the value of the type attribute is the content's type.

  2. Otherwise, if the <path> component of the URL of the specified resource matches a pattern that a plugin supports, then the content's type is the type that that plugin can handle.

    For example, a plugin might say that it can handle resources with <path> components that end with the four character string ".swf".

    It would be better if browsers didn't do extension sniffing like this, and only based their decision on the actual contents of the resource. Couldn't we just apply the sniffed type of a resource steps?

  3. Otherwise, if the specified resource has explicit Content-Type metadata, then that is the content's type.

  4. Otherwise, the content has no type and there can be no appropriate plugin for it.

Whether the resource is fetched successfully or not (e.g. whether the response code was a 2xx code or equivalent) must be ignored when determining the resource's type and when handing the resource to the plugin.

This allows servers to return data for plugins even with error responses (e.g. HTTP 500 Internal Server Error codes can still contain plugin data).

When the element is created with a type attribute and no src attribute, and whenever the type attribute is subsequently set, so long as no src attribute is set, and whenever the src attribute is removed when the element has a type attribute, if the element is not in a sandboxed browsing context, user agents should find and instantiate an appropriate plugin based on the value of the type attribute.

Any (namespace-less) attribute may be specified on the embed element, so long as its name is XML-compatible and contains no characters in the range U+0041 .. U+005A (LATIN CAPITAL LETTER A LATIN CAPITAL LETTER Z).

All attributes in HTML documents get lowercased automatically, so the restriction on uppercase letters doesn't affect such documents.

The user agent should pass the names and values of all the attributes of the embed element that have no namespace to the plugin used, when it is instantiated.

If the plugin instantiated for the embed element supports a scriptable interface, the HTMLEmbedElement object representing the element should expose that interface while the element is instantiated.

The embed element has no fallback content. If the user agent can't find a suitable plugin, then the user agent must use a default plugin. (This default could be as simple as saying "Unsupported Format".)

The embed element supports dimension attributes.

The DOM attributes src and type each must reflect the respective content attributes of the same name.

4.8.5 The object element

Categories
Flow content.
Phrasing content.
Embedded content.
Listed, submittable, form-associated element.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Zero or more param elements, then, transparent.
Content attributes:
Global attributes
data
type
name
usemap
form
width
height
DOM interface:
interface HTMLObjectElement : HTMLElement {
           attribute DOMString data;
           attribute DOMString type;
           attribute DOMString name;
           attribute DOMString useMap;
  readonly attribute HTMLFormElement form;
           attribute DOMString width;
           attribute DOMString height;
};

Objects implementing the HTMLObjectElement interface must also implement the EmbeddingElement interface defined in the Window Object specification. [WINDOW]

Depending on the type of content instantiated by the object element, the node may also support other interfaces.

The object element can represent an external resource, which, depending on the type of the resource, will either be treated as an image, as a nested browsing context, or as an external resource to be processed by a plugin.

The data attribute, if present, specifies the address of the resource. If present, the attribute must be a valid URL.

The type attribute, if present, specifies the type of the resource. If present, the attribute must be a valid MIME type, optionally with parameters. [RFC2046]

One or both of the data and type attributes must be present.

The name attribute, if present, must be a valid browsing context name. The given value is used to name the nested browsing context, if applicable.

When the element is created, and subsequently whenever the classid attribute changes or is removed, or, if the classid attribute is not present, whenever the data attribute changes or is removed, or, if neither classid attribute nor the data attribute are present, whenever the type attribute changes or is removed, the user agent must run the following steps to determine what the object element represents:

  1. If the element has an ancestor object element that is not showing its fallback content, then jump to the last step in the overall set of steps (fallback).

  2. If the classid attribute is present, and has a value that isn't the empty string, then: if the user agent can find a plugin suitable according to the value of the classid attribute, and plugins aren't being sandboxed, then that plugin should be used, and the value of the data attribute, if any, should be passed to the plugin. If no suitable plugin can be found, or if the plugin reports an error, jump to the last step in the overall set of steps (fallback).

  3. If the data attribute is present, then:

    1. If the type attribute is present and its value is not a type that the user agent supports, and is not a type that the user agent can find a plugin for, then the user agent may jump to the last step in the overall set of steps (fallback) without fetching the content to examine its real type.

    2. Resolve the URL specified by the data attribute, relative to the element.

      If that is successful, fetch the resulting absolute URL.

      Fetching the resource must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined next) has been run.

    3. If the resource is not yet available (e.g. because the resource was not available in the cache, so that loading the resource required making a request over the network), then jump to the last step in the overall set of steps (fallback). The task that is queued by the networking task source once the resource is available must restart this algorithm from this step. Resources can load incrementally; user agents may opt to consider a resource "available" whenever enough data has been obtained to begin processing the resource.

    4. If the load failed (e.g. the URL could not be resolved, there was an HTTP 404 error, there was a DNS error), fire a simple event called error at the element, then jump to the last step in the overall set of steps (fallback).

    5. Determine the resource type, as follows:

      1. Let the resource type be unknown.

      2. If the resource has associated Content-Type metadata, then let the resource type be the type specified in the resource's Content-Type metadata.

      3. If the resource type is unknown or "application/octet-stream" and there is a type attribute present on the object element, then change the resource type to instead be the type specified in that type attribute.

        Otherwise, if the resource type is "application/octet-stream" but there is no type attribute on the object element, then change the resource type to be unknown, so that the sniffing rules in the next step are invoked.

      4. If the resource type is still unknown, then change the resource type to instead be the sniffed type of the resource.

    6. Handle the content as given by the first of the following cases that matches:

      If the resource type can be handled by a plugin and plugins aren't being sandboxed

      The user agent should use that plugin and pass the content of the resource to that plugin. If the plugin reports an error, then jump to the last step in the overall set of steps (fallback).

      If the resource type is an XML MIME type
      If the resource type is HTML
      If the resource type does not start with "image/"

      The object element must be associated with a nested browsing context, if it does not already have one. The element's nested browsing context must then be navigated to the given resource, with replacement enabled, and with the object element's document's browsing context as the source browsing context. (The data attribute of the object element doesn't get updated if the browsing context gets further navigated to other locations.)

      The object element represents the nested browsing context.

      If the name attribute is present, the browsing context name must be set to the value of this attribute; otherwise, the browsing context name must be set to the empty string.

      navigation might end up treating it as something else, because it can do sniffing. how should we handle that? it could also refetch the resource entirely, maybe from another application cache.

      If the resource type starts with "image/", and support for images has not been disabled

      Apply the image sniffing rules to determine the type of the image.

      The object element represents the specified image. The image is not a nested browsing context.

      If the image cannot be rendered, e.g. because it is malformed or in an unsupported format, jump to the last step in the overall set of steps (fallback).

      Otherwise

      The given resource type is not supported. Jump to the last step in the overall set of steps (fallback).

    7. The element's contents are not part of what the object element represents.

    8. Once the resource is completely loaded, fire a simple event called load at the element.

  4. If the data attribute is absent but the type attribute is present, plugins aren't being sandboxed, and the user agent can find a plugin suitable according to the value of the type attribute, then that plugin should be used. If no suitable plugin can be found, or if the plugin reports an error, jump to the next step (fallback).

  5. (Fallback.) The object element represents the element's children, ignoring any leading param element children. This is the element's fallback content.

When the algorithm above instantiates a plugin, the user agent should pass the names and values of all the attributes on the element, and all the names and values of parameters given by param elements that are children of the object element, in tree order, to the plugin used. If the plugin supports a scriptable interface, the HTMLObjectElement object representing the element should expose that interface. The object element represents the plugin. The plugin is not a nested browsing context.

If the sandboxed plugins browsing context flag is set on the browsing context for which the object element's document is the active document, then the steps above must always act as if they had failed to find a plugin, even if one would otherwise have been used.

Due to the algorithm above, the contents of object elements act as fallback content, used only when referenced resources can't be shown (e.g. because it returned a 404 error). This allows multiple object elements to be nested inside each other, targeting multiple user agents with different capabilities, with the user agent picking the first one it supports.

Whenever the name attribute is set, if the object element has a nested browsing context, its name must be changed to the new value. If the attribute is removed, if the object element has a browsing context, the browsing context name must be set to the empty string.

The usemap attribute, if present while the object element represents an image, can indicate that the object has an associated image map. The attribute must be ignored if the object element doesn't represent an image.

The form attribute is used to explicitly associate the object element with its form owner.

Constraint validation: object elements are always barred from constraint validation.

The object element supports dimension attributes.

The DOM attributes data, type, name, and useMap each must reflect the respective content attributes of the same name.

In the following example, a Java applet is embedded in a page using the object element. (Generally speaking, it is better to avoid using applets like these and instead use native JavaScript and HTML to provide the functionality, since that way the application will work on all Web browsers without requiring a third-party plugin. Many devices, especially embedded devices, do not support third-party technologies like Java.)

<figure>
 <object type="application/x-java-applet">
  <param name="code" value="MyJavaClass">
  <p>You do not have Java available, or it is disabled.</p>
 </object>
 <legend>My Java Clock</legend>
</figure>

In this example, an HTML page is embedded in another using the object element.

<figure>
 <object data="clock.html"></object>
 <legend>My HTML Clock</legend>
</figure>

4.8.6 The param element

Categories
None.
Contexts in which this element may be used:
As a child of an object element, before any flow content.
Content model:
Empty.
Content attributes:
Global attributes
name
value
DOM interface:
interface HTMLParamElement : HTMLElement {
           attribute DOMString name;
           attribute DOMString value;
};

The param element defines parameters for plugins invoked by object elements. It does not represent anything on its own.

The name attribute gives the name of the parameter.

The value attribute gives the value of the parameter.

Both attributes must be present. They may have any value.

If both attributes are present, and if the parent element of the param is an object element, then the element defines a parameter with the given name/value pair.

The DOM attributes name and value must both reflect the respective content attributes of the same name.

4.8.7 The video element

Categories
Flow content.
Phrasing content.
Embedded content.
If the element has a controls attribute: Interactive content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
If the element has a src attribute: transparent.
If the element does not have a src attribute: one or more source elements, then, transparent.
Content attributes:
Global attributes
src
poster
autobuffer
autoplay
loop
controls
width
height
DOM interface:
interface HTMLVideoElement : HTMLMediaElement {
           attribute DOMString width;
           attribute DOMString height;
  readonly attribute unsigned long videoWidth;
  readonly attribute unsigned long videoHeight;
           attribute DOMString poster;
};

A video element represents a video or movie.

Content may be provided inside the video element. User agents should not show this content to the user; it is intended for older Web browsers which do not support video, so that legacy video plugins can be tried, or to show text to the users of these older browser informing them of how to access the video contents.

In particular, this content is not fallback content intended to address accessibility concerns. To make video content accessible to the blind, deaf, and those with other physical or cognitive disabilities, authors are expected to provide alternative media streams and/or to embed accessibility aids (such as caption or subtitle tracks) into their media streams.

The video element is a media element whose media data is ostensibly video data, possibly with associated audio data.

The src, autobuffer, autoplay, loop, and controls attributes are the attributes common to all media elements.

The poster attribute gives the address of an image file that the user agent can show while no video data is available. The attribute, if present, must contain a valid URL. If the specified resource is to be used, then, when the element is created or when the poster attribute is set, its value must be resolved relative to the element, and if that is successful, the resulting absolute URL must be fetched; this must delay the load event of the element's document. The poster frame is then the image obtained from that resource, if any.

The image given by the poster attribute, the poster frame, is intended to be a representative frame of the video (typically one of the first non-blank frames) that gives the user an idea of what the video is like.

The poster DOM attribute must reflect the poster content attribute.


When no video data is available (the element's readyState attribute is either HAVE_NOTHING, or HAVE_METADATA but no video data has yet been obtained at all), the video element represents either the poster frame, or nothing.

When a video element is paused and the current playback position is the first frame of video, the element represents either the frame of video corresponding to the current playback position or the poster frame, at the discretion of the user agent.

Notwithstanding the above, the poster frame should be preferred over nothing, but the poster frame should not be shown again after a frame of video has been shown.

When a video element is paused at any other position, the element represents the frame of video corresponding to the current playback position, or, if that is not yet available (e.g. because the video is seeking or buffering), the last frame of the video to have been rendered.

When a video element is potentially playing, it represents the frame of video at the continuously increasing "current" position. When the current playback position changes such that the last frame rendered is no longer the frame corresponding to the current playback position in the video, the new frame must be rendered. Similarly, any audio associated with the video must, if played, be played synchronized with the current playback position, at the specified volume with the specified mute state.

When a video element is neither potentially playing nor paused (e.g. when seeking or stalled), the element represents the last frame of the video to have been rendered.

Which frame in a video stream corresponds to a particular playback position is defined by the video stream's format.

In addition to the above, the user agent may provide messages to the user (such as "buffering", "no video loaded", "error", or more detailed information) by overlaying text or icons on the video or other areas of the element's playback area, or in another appropriate manner.

User agents that cannot render the video may instead make the element represent a link to an external video playback utility or to the video data itself.


video . videoWidth
video . videoHeight

These attributes return the intrinsic dimensions of the video, or zero if the dimensions are not known.

The intrinsic width and intrinsic height of the media resource are the dimensions of the resource in CSS pixels after taking into account the resource's dimensions, aspect ratio, clean aperture, resolution, and so forth, as defined for the format used by the resource.

The videoWidth DOM attribute must return the intrinsic width of the video in CSS pixels. The videoHeight DOM attribute must return the intrinsic height of the video in CSS pixels. If the element's readyState attribute is HAVE_NOTHING, then the attributes must return 0.

The video element supports dimension attributes.

Video content should be rendered inside the element's playback area such that the video content is shown centered in the playback area at the largest possible size that fits completely within it, with the video content's aspect ratio being preserved. Thus, if the aspect ratio of the playback area does not match the aspect ratio of the video, the video will be shown letterboxed or pillarboxed. Areas of the element's playback area that do not contain the video represent nothing.

The intrinsic width of a video element's playback area is the intrinsic width of the video resource, if that is available; otherwise it is the intrinsic width of the poster frame, if that is available; otherwise it is 300 CSS pixels.

The intrinsic height of a video element's playback area is the intrinsic height of the video resource, if that is available; otherwise it is the intrinsic height of the poster frame, if that is available; otherwise it is 150 CSS pixels.


User agents should provide controls to enable or disable the display of closed captions associated with the video stream, though such features should, again, not interfere with the page's normal rendering.

User agents may allow users to view the video content in manners more suitable to the user (e.g. full-screen or in an independent resizable window). As for the other user interface features, controls to enable this should not interfere with the page's normal rendering unless the user agent is exposing a user interface. In such an independent context, however, user agents may make full user interfaces visible, with, e.g., play, pause, seeking, and volume controls, even if the controls attribute is absent.

User agents may allow video playback to affect system features that could interfere with the user's experience; for example, user agents could disable screensavers while video playback is in progress.

User agents should not provide a public API to cause videos to be shown full-screen. A script, combined with a carefully crafted video file, could trick the user into thinking a system-modal dialog had been shown, and prompt the user for a password. There is also the danger of "mere" annoyance, with pages launching full-screen videos when links are clicked or pages navigated. Instead, user-agent specific interface features may be provided to easily allow the user to obtain a full-screen playback mode.

4.8.7.1 Video and audio codecs for video elements

User agents may support any video and audio codecs and container formats.

It would be helpful for interoperability if all browsers could support the same codecs. However, there are no known codecs that satisfy all the current players: we need a codec that is known to not require per-unit or per-distributor licensing, that is compatible with the open source development model, that is of sufficient quality as to be usable, and that is not an additional submarine patent risk for large companies. This is an ongoing issue and this section will be updated once more information is available.

Certain user agents might support no codecs at all, e.g. text browsers running over SSH connections.

4.8.8 The audio element

Categories
Flow content.
Phrasing content.
Embedded content.
If the element has a controls attribute: Interactive content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
If the element has a src attribute: transparent.
If the element does not have a src attribute: one or more source elements, then, transparent.
Content attributes:
Global attributes
src
autobuffer
autoplay
loop
controls
DOM interface:
[NamedConstructor=Audio(),
 NamedConstructor=Audio(in DOMString src)]
interface HTMLAudioElement : HTMLMediaElement {
  // no members
};

An audio element represents a sound or audio stream.

Content may be provided inside the audio element. User agents should not show this content to the user; it is intended for older Web browsers which do not support audio, so that legacy audio plugins can be tried, or to show text to the users of these older browser informing them of how to access the audio contents.

In particular, this content is not fallback content intended to address accessibility concerns. To make audio content accessible to the deaf or to those with other physical or cognitive disabilities, authors are expected to provide alternative media streams and/or to embed accessibility aids (such as transcriptions) into their media streams.

The audio element is a media element whose media data is ostensibly audio data.

The src, autobuffer, autoplay, loop, and controls attributes are the attributes common to all media elements.

When an audio element is potentially playing, it must have its audio data played synchronized with the current playback position, at the specified volume with the specified mute state.

When an audio element is not potentially playing, audio must not play for the element.

audio = new Audio( [ url ] )

Returns a new audio element, with the src attribute set to the value passed in the argument, if applicable.

Two constructors are provided for creating HTMLAudioElement objects (in addition to the factory methods from DOM Core such as createElement()): Audio() and Audio(src). When invoked as constructors, these must return a new HTMLAudioElement object (a new audio element). If the src argument is present, the object created must have its src content attribute set to the provided value, and the user agent must invoke the object's resource selection algorithm before returning.

4.8.8.1 Audio codecs for audio elements

User agents may support any audio codecs and container formats.

User agents must support the WAVE container format with audio encoded using the PCM format.

4.8.9 The source element

Categories
None.
Contexts in which this element may be used:
As a child of a media element, before any flow content.
Content model:
Empty.
Content attributes:
Global attributes
src
type
media
DOM interface:
interface HTMLSourceElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString type;
           attribute DOMString media;
};

The source element allows authors to specify multiple media resources for media elements. It does not represent anything on its own.

The src attribute gives the address of the media resource. The value must be a valid URL. This attribute must be present.

The type attribute gives the type of the media resource, to help the user agent determine if it can play this media resource before fetching it. If specified, its value must be a MIME type. The codecs parameter may be specified and might be necessary to specify exactly how the resource is encoded. [RFC2046] [RFC4281]

The following list shows some examples of how to use the codecs= MIME parameter in the type attribute.

H.264 Simple baseline profile video (main and extended video compatible) level 3 and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;avc1.42E01E, mp4a.40.2&quot;">
H.264 Extended profile video (baseline-compatible) level 3 and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;avc1.58A01E, mp4a.40.2&quot;">
H.264 Main profile video level 3 and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;avc1.4D401E, mp4a.40.2&quot;">
H.264 "High" profile video (incompatible with main, baseline, or extended profiles) level 3 and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;avc1.64001E, mp4a.40.2&quot;">
MPEG-4 Visual Simple Profile Level 0 video and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;mp4v.20.8, mp4a.40.2&quot;">
MPEG-4 Advanced Simple Profile Level 0 video and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;mp4v.20.240, mp4a.40.2&quot;">
MPEG-4 Visual Simple Profile Level 0 video and AMR audio in 3GPP container
<source src="video.3gp" type="video/3gpp; codecs=&quot;mp4v.20.8, samr&quot;">
Theora video and Vorbis audio in Ogg container
<source src="video.ogv" type="video/ogg; codecs=&quot;theora, vorbis&quot;">
Theora video and Speex audio in Ogg container
<source src="video.ogv" type="video/ogg; codecs=&quot;theora, speex&quot;">
Vorbis audio alone in Ogg container
<source src="audio.ogg" type="audio/ogg; codecs=vorbis">
Speex audio alone in Ogg container
<source src="audio.spx" type="audio/ogg; codecs=speex">
FLAC audio alone in Ogg container
<source src="audio.oga" type="audio/ogg; codecs=flac">
Dirac video and Vorbis audio in Ogg container
<source src="video.ogv" type="video/ogg; codecs=&quot;dirac, vorbis&quot;">
Theora video and Vorbis audio in Matroska container
<source src="video.mkv" type="video/x-matroska; codecs=&quot;theora, vorbis&quot;">

The media attribute gives the intended media type of the media resource, to help the user agent determine if this media resource is useful to the user before fetching it. Its value must be a valid media query. [MQ]

The DOM attributes src, type, and media must reflect the respective content attributes of the same name.

4.8.10 Media elements

Media elements implement the following interface:

interface HTMLMediaElement : HTMLElement {

  // error state
  readonly attribute MediaError error;

  // network state
           attribute DOMString src;
  readonly attribute DOMString currentSrc;
  const unsigned short NETWORK_EMPTY = 0;
  const unsigned short NETWORK_IDLE = 1;
  const unsigned short NETWORK_LOADING = 2;
  const unsigned short NETWORK_LOADED = 3;
  const unsigned short NETWORK_NO_SOURCE = 4;
  readonly attribute unsigned short networkState;
           attribute boolean autobuffer;
  readonly attribute TimeRanges buffered;
  void load();
  DOMString canPlayType(in DOMString type);

  // ready state
  const unsigned short HAVE_NOTHING = 0;
  const unsigned short HAVE_METADATA = 1;
  const unsigned short HAVE_CURRENT_DATA = 2;
  const unsigned short HAVE_FUTURE_DATA = 3;
  const unsigned short HAVE_ENOUGH_DATA = 4;
  readonly attribute unsigned short readyState;
  readonly attribute boolean seeking;

  // playback state
           attribute float currentTime;
  readonly attribute float startTime;
  readonly attribute float duration;
  readonly attribute boolean paused;
           attribute float defaultPlaybackRate;
           attribute float playbackRate;
  readonly attribute TimeRanges played;
  readonly attribute TimeRanges seekable;
  readonly attribute boolean ended;
           attribute boolean autoplay;
           attribute boolean loop;
  void play();
  void pause();

  // cue ranges
  void addCueRange(in DOMString className, in DOMString id, in float start, in float end, in boolean pauseOnExit, in CueRangeCallback enterCallback, in CueRangeCallback exitCallback);
  void removeCueRanges(in DOMString className);

  // controls
           attribute boolean controls;
           attribute float volume;
           attribute boolean muted;
};

[Callback=FunctionOnly, NoInterfaceObject]
interface CueRangeCallback {
  void handleEvent(in DOMString id);
};

The media element attributes, src, autobuffer, autoplay, loop, and controls, apply to all media elements. They are defined in this section.

Media elements are used to present audio data, or video and audio data, to the user. This is referred to as media data in this section, since this section applies equally to media elements for audio or for video. The term media resource is used to refer to the complete set of media data, e.g. the complete video file, or complete audio file.

Unless otherwise specified, the task source for all the tasks queued in this section and its subsections is the media element event task source.

4.8.10.1 Error codes
media . error

Returns a MediaError object representing the current error state of the element.

Returns null if there is no error.

All media elements have an associated error status, which records the last error the element encountered since its resource selection algorithm was last invoked. The error attribute, on getting, must return the MediaError object created for this last error, or null if there has not been an error.

interface MediaError {
  const unsigned short MEDIA_ERR_ABORTED = 1;
  const unsigned short MEDIA_ERR_NETWORK = 2;
  const unsigned short MEDIA_ERR_DECODE = 3;
  const unsigned short MEDIA_ERR_SRC_NOT_SUPPORTED = 4;
  readonly attribute unsigned short code;
};
media . error . code

Returns the current error's error code, from the list below.

The code attribute of a MediaError object must return the code for the error, which must be one of the following:

MEDIA_ERR_ABORTED (numeric value 1)
The fetching process for the media resource was aborted by the user agent at the user's request.
MEDIA_ERR_NETWORK (numeric value 2)
A network error of some description caused the user agent to stop fetching the media resource, after the resource was established to be usable.
MEDIA_ERR_DECODE (numeric value 3)
An error of some description occurred while decoding the media resource, after the resource was established to be usable.
MEDIA_ERR_SRC_NOT_SUPPORTED (numeric value 4)
The media resource indicated by the src attribute was not suitable.
4.8.10.2 Location of the media resource

The src content attribute on media elements gives the address of the media resource (video, audio) to show. The attribute, if present, must contain a valid URL.

The src DOM attribute on media elements must reflect the respective content attribute of the same name.

media . currentSrc

Returns the address of the current media resource.

Returns the empty string when there is no media resource.

The currentSrc DOM attribute is initially the empty string. Its value is changed by the resource selection algorithm defined below.

There are two ways to specify a media resource, the src attribute, or source elements. The attribute overrides the elements.

4.8.10.3 Media types

A media resource can be described in terms of its type, specifically a MIME type, optionally with a codecs parameter. [RFC2046] [RFC4281].

Types are usually somewhat incomplete descriptions; for example "video/mpeg" doesn't say anything except what the container type is, and even a type like "video/mp4; codecs="avc1.42E01E, mp4a.40.2"" doesn't include information like the actual bitrate (only the maximum bitrate). Thus, given a type, a user agent can often only know whether it might be able to play media of that type (with varying levels of confidence), or whether it definitely cannot play media of that type.

A type that the user agent knows it cannot render is one that describes a resource that the user agent definitely does not support, for example because it doesn't recognize the container type, or it doesn't support the listed codecs.

media . canPlayType(type)

Returns "no", "maybe", or "probably" based on how confident the user agent is that it can play media resources of the given type.

The canPlayType(type) method must return the string "no" if type is a type that the user agent knows it cannot render; it must return "probably" if the user agent is confident that the type represents a media resource that it can render if used in with this audio or video element; and it must return "maybe" otherwise. Implementors are encouraged to return "maybe" unless the type can be confidently established as being supported or not. Generally, a user agent should never return "probably" if the type doesn't have a codecs parameter.

This script tests to see if the user agent supports a (fictional) new format to dynamically decide whether to use a video element or a plugin:

<section id="video">
 <p><a href="playing-cats.nfv">Download video</a></p>
</section>
<script>
 var videoSection = document.getElementById('video');
 var videoElement = document.createElement('video');
 var support = videoElement.canPlayType('video/x-new-fictional-format;codecs="kittens,bunnies"');
 if (support != "probably" && "New Fictional Video Plug-in" in navigator.plugins) {
   // not confident of browser support
   // but we have a plugin
   // so use plugin instead
   videoElement = document.createElement("embed");
 } else if (support == "no") {
   // no support from browser and no plugin
   // do nothing
   videoElement = null;
 }
 if (videoElement) {
   while (videoSection.hasChildNodes())
     videoSection.removeChild(videoSection.firstChild);
   videoElement.setAttribute("src", "playing-cats.nfv");
   videoSection.appendChild(videoElement);
 }
</script>

To express the type of a media resource to allow the user agent to avoid downloading resources it can't render, authors can use the source element's type attribute.

4.8.10.4 Network states
media . networkState

Returns the current state of network activity for the element, from the codes in the list below.

As media elements interact with the network, their current network activity is represented by the networkState attribute. On getting, it must return the current network state of the element, which must be one of the following values:

NETWORK_EMPTY (numeric value 0)
The element has not yet been initialized. All attributes are in their initial states.
NETWORK_IDLE (numeric value 1)
The element's resource selection algorithm is active and has selected a resource, but it is not actually using the network at this time.
NETWORK_LOADING (numeric value 2)
The user agent is actively trying to download data.
NETWORK_LOADED (numeric value 3)
The entire media resource has been obtained and is available to the user agent locally. Network connectivity could be lost without affecting the media playback.
NETWORK_NO_SOURCE (numeric value 4)
The element's resource selection algorithm is active, but it has failed to find a resource to use.

The resource selection algorithm defined below describes exactly when the networkState attribute changes value and what events fire to indicate changes in this state.

Some resources, e.g. streaming Web radio, can never reach the NETWORK_LOADED state.

4.8.10.5 Loading the media resource
media . load()

Causes the element to reset and start selecting and loading a new media resource from scratch.

All media elements have an autoplaying flag, which must begin in the true state, and a delaying-the-load-event flag, which must begin in the false state. While the delaying-the-load-event flag is true, the element must delay the load event of its document.

When the load() method on a media element is invoked, the user agent must run the following steps. Note that this algorithm might get aborted, e.g. if the load() method itself is invoked again.

  1. If the load() method for this element is already being invoked, then abort these steps.

  2. Abort any already-running instance of the resource selection algorithm for this element.

  3. If there are any tasks from the media element's media element event task source in one of the task queues, then remove those tasks.

    Basically, pending events and callbacks for the media element are discarded when the media element starts loading a new resource.

  4. If the media element's networkState is set to NETWORK_LOADING or NETWORK_IDLE, set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_ABORTED, and fire a progress event called abort at the media element.

  5. Set the error attribute to null and the autoplaying flag to true.

  6. Set the playbackRate attribute to the value of the defaultPlaybackRate attribute.

  7. If the media element's networkState is not set to NETWORK_EMPTY, then run these substeps:

    1. If a fetching process is in progress for the media element, the user agent should stop it.

    2. Set the networkState attribute to NETWORK_EMPTY.
    3. If readyState is not set to HAVE_NOTHING, then set it to that state.
    4. If the paused attribute is false, then set to true.
    5. If seeking is true, set it to false.
    6. Set the current playback position to 0.
    7. Fire a simple event called emptied at the media element.
  8. Invoke the media element's resource selection algorithm.

  9. Playback of any previously playing media resource for this element stops.

The resource selection algorithm for a media element is as follows. This algorithm is always invoked synchronously, but one of the first steps in the algorithm is to return and continue running the remaining steps asynchronously, meaning that it runs in the background with scripts and other tasks running in parallel.

  1. If the media element has neither a src attribute nor any source element children, run these substeps:

    1. Set the networkState to NETWORK_NO_SOURCE.

    2. Run the remainder of the resource selection algorithm steps asynchronously, allowing the task that invoked this algorithm to continue.

    3. While the media element has neither a src attribute nor any source element children, wait. (This step might wait forever.)

    4. Before the task that set the src attribute or inserted the source element has a chance to complete, set the media element's delaying-the-load-event flag to true (this delays the load event), and set its networkState to NETWORK_LOADING.

    5. If a src attribute was set before a source element was inserted, let src equal the first value that was assigned to the src attribute after this algorithm was invoked.

    Otherwise, run these substeps:

    1. Set the media element's delaying-the-load-event flag to true (this delays the load event), and set its networkState to NETWORK_LOADING.

    2. If the media element has a src attribute, let src equal the value of that attribute.

    3. Run the remainder of the resource selection algorithm steps asynchronously, allowing the task that invoked this algorithm to continue.

  2. By this point, the algorithm is running asynchronously.

  3. Queue a task to fire a progress event called loadstart at the media element.

  4. If src was given a value in the earlier steps, then run these substeps:

    1. Let absolute URL be the absolute URL that would have resulted from resolving the URL given by src relative to the media element when the src attribute was set to src.

    2. If absolute URL was successfully obtained, then run the resource fetch algorithm with absolute URL. If that algorithm returns without aborting this one, then the load failed.

    3. Reaching this step indicates that either the URL failed to resolve, or the media resource failed to load. Set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_SRC_NOT_SUPPORTED.

    4. Set the element's networkState attribute to the NETWORK_NO_SOURCE value.

    5. Queue a task to fire a progress event called error at the media element.

    6. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.

    7. Abort these steps. Until the load() method is invoked, the element won't attempt to load another resource.

    Otherwise, the source elements will be used; run these substeps:

    1. Let pointer be a position defined by two adjacent nodes in the media element's child list, treating the start of the list (before the first child in the list, if any) and end of the list (after the last child in the list, if any) as nodes in their own right. One node is the node before pointer, and the other node is the node after pointer. Initially, let pointer be the position between the start of the list and the next node (either the first child node of the media element, if there are any, or the end of the list, if it is empty).

      As elements are inserted and removed into the media element, pointer must be updated as follows:

      If a new element is inserted between the two nodes that define pointer
      Let pointer be the point between the node before pointer and the new node. In other words, insertions at pointer go after pointer.
      If the node before pointer is removed
      Let pointer be the point between the node after pointer and the node before the node after pointer. In other words, pointer doesn't move relative to the remaining nodes.
      If the node after pointer is removed
      Let pointer be the point between the node before pointer and the node after the node before pointer. Just as with the previous case, pointer doesn't move relative to the remaining nodes.

      Other changes don't affect pointer.

    2. Search loop: Queue a task to run the following steps (so that no other tasks are running that could make the DOM change while these steps are running):

      1. Let candidate be null.

      2. If the node after pointer is the end of the list, then abort the task.

      3. If the node after pointer is a source element, let candidate be that element.

      4. Advance pointer so that the node before pointer is now the node that was after pointer, and the node after pointer is the node after the node that used to be after pointer.

      5. If candidate is null, restart these substeps from the first substep. Otherwise, abort the task.

      6. Resolve the URL given by the candidate element's src attribute relative to candidate.

      Wait for the task to run. When the task ends, if candidate is null, then jump to the step below labeled waiting. Otherwise, continue with the next step.

    3. If any of the following conditions are true, then queue a task to fire a simple event called error at the candidate element and then jump back to the step labelled search loop:

      • The candidate element does not have a src attribute.
      • Resolving the URL given by the candidate element's src attribute relative to candidate failed.
      • The candidate element has a type attribute whose value, when parsed as a MIME type (including any codecs described by the codec parameter), represents a type that the user agent knows it cannot render.
      • The candidate element has a media attribute whose value, when processed according to the rules for media queries, does not match the current environment. [MQ]
    4. Set the networkState to NETWORK_LOADING again, in case it was set to NETWORK_NO_SOURCE above.

    5. Run the resource fetch algorithm with the absolute URL that resulted from resolving the URL given by the candidate element's src attribute relative to candidate. If that algorithm returns without aborting this one, then the load failed.

    6. Queue a task to fire a simple event called error at the candidate element.

    7. Return to the step labeled search loop.

    8. Waiting: Set the element's networkState attribute to the NETWORK_NO_SOURCE value

    9. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.

    10. Wait until the node after pointer is a node other than the end of the list. (This step might wait forever.)

    11. Before the task that inserted the source element has a chance to complete, set the element's delaying-the-load-event flag back to true. This delays the load event again, in case it hasn't been fired yet.

    12. Jump back to the step labeled search loop.

The resource fetch algorithm for a media element and a given absolute URL is as follows:

  1. Let the current media resource be the resource given by the absolute URL passed to this algorithm. This is now the element's media resource.

  2. Set the currentSrc attribute to the absolute URL of the current media resource.

  3. Begin to fetch the current media resource.

    Every 350ms (±200ms) or for every byte received, whichever is least frequent, queue a task to fire a progress event called progress at the element.

    If at any point the user agent has received no data for more than about three seconds, then queue a task to fire a progress event called stalled at the element.

    User agents may allow users to selectively block or slow media data downloads. When a media element's download has been blocked altogether, the user agent must act as if it was stalled (as opposed to acting as if the connection was closed). The rate of the download may also be throttled automatically by the user agent, e.g. to balance the download with other connections sharing the same bandwidth.

    User agents may decide to not download more content at any time, e.g. after buffering five minutes of a one hour media resource, while waiting for the user to decide whether to play the resource or not, or while waiting for user input in an interactive resource. When a media element's download has been suspended, the user agent must set the networkState to NETWORK_IDLE and queue a task to fire a progress event called suspend at the element. If and when downloading of the resource resumes, the user agent must set the networkState to NETWORK_LOADING.

    The autobuffer attribute provides a hint that the author expects that downloading the entire resource optimistically will be worth it, even in the absence of the autoplay attribute. In the absence of either attribute, the user agent is likely to find that waiting until the user starts playback before downloading any further content leads to a more efficient use of the network resources.

    When a user agent decides to completely stall a download, e.g. if it is waiting until the user starts playback before downloading any further content, the element's delaying-the-load-event flag must be set to false. This stops delaying the load event.

    The user agent may use whatever means necessary to fetch the resource (within the constraints put forward by this and other specifications); for example, reconnecting to the server in the face of network errors, using HTTP partial range requests, or switching to a streaming protocol. The user agent must consider a resource erroneous only if it has given up trying to fetch it.

    The networking task source tasks to process the data as it is being fetched must, when appropriate, include the relevant substeps from the following list:

    If the media data cannot be fetched at all, due to network errors, causing the user agent to give up trying to fetch the resource
    If the media data can be fetched but is in an unsupported format, or can otherwise not be rendered at all

    DNS errors, HTTP 4xx and 5xx errors (and equivalents in other protocols), and other fatal network errors that occur before the user agent has established whether the current media resource is usable, as well as the file using an unsupported container format, or using unsupported codecs for all the data, must cause the user agent to execute the following steps:

    1. The user agent should cancel the fetching process.

    2. Abort this subalgorithm, returning to the resource selection algorithm.

    Once enough of the media data has been fetched to determine the duration of the media resource, its dimensions, and other metadata

    This indicates that the resource is usable. The user agent must follow these substeps:

    1. Set the current playback position to the earliest possible position.

    2. Set the readyState attribute to HAVE_METADATA.

    3. For video elements, set the videoWidth and videoHeight attributes.

    4. Set the duration attribute to the duration of the resource.

      The user agent will queue a task to fire a simple event called durationchange at the element at this point.

    5. Queue a task to fire a simple event called loadedmetadata at the element.

    6. If either the media resource or the address of the current media resource indicate a particular start time, then seek to that time. Ignore any resulting exceptions (if the position is out of range, it is effectively ignored).

      For example, a fragment identifier could be used to indicate a start position.

    7. Once the readyState attribute reaches HAVE_CURRENT_DATA, after the loadeddata event has been fired, set the element's delaying-the-load-event flag to false. This stops delaying the load event.

      A user agent that is attempting to reduce network usage while still fetching the metadata for each media resource would also stop buffering at this point, causing the networkState attribute to switch to the NETWORK_IDLE value, if the media element did not have an autobuffer or autoplay attribute.

    The user agent is required to determine the duration of the media resource and go through this step before playing.

    If the connection is interrupted, causing the user agent to give up trying to fetch the resource

    Fatal network errors that occur after the user agent has established whether the current media resource is usable must cause the user agent to execute the following steps:

    1. The user agent should cancel the fetching process.

    2. Set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_NETWORK.

    3. Queue a task to fire a progress event called error at the media element.

    4. Set the element's networkState attribute to the NETWORK_EMPTY value and queue a task to fire a simple event called emptied at the element.

    5. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.

    6. Abort the overall resource selection algorithm.

    If the media data is corrupted

    Fatal errors in decoding the media data that occur after the user agent has established whether the current media resource is usable must cause the user agent to execute the following steps:

    1. The user agent should cancel the fetching process.

    2. Set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_DECODE.

    3. Queue a task to fire a progress event called error at the media element.

    4. Set the element's networkState attribute to the NETWORK_EMPTY value and queue a task to fire a simple event called emptied at the element.

    5. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.

    6. Abort the overall resource selection algorithm.

    If the media data fetching process is aborted by the user

    The fetching process is aborted by the user, e.g. because the user navigated the browsing context to another page, the user agent must execute the following steps. These steps are not followed if the load() method itself is invoked while these steps are running, as the steps above handle that particular kind of abort.

    1. The user agent should cancel the fetching process.

    2. Set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_ABORT.

    3. Queue a task to fire a progress event called abort at the media element.

    4. If the media element's readyState attribute has a value equal to HAVE_NOTHING, set the element's networkState attribute to the NETWORK_EMPTY value and queue a task to fire a simple event called emptied at the element. Otherwise, set the element's networkState attribute to the NETWORK_IDLE value.

    5. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.

    6. Abort the overall resource selection algorithm.

    If the media data can be fetched but has non-fatal errors or uses, in part, codecs that are unsupported, preventing the user agent from rendering the content completely correctly but not preventing playback altogether

    The server returning data that is partially usable but cannot be optimally rendered must cause the user agent to execute the following steps.

    1. Should we fire a 'warning' event? Set the 'error' flag to 'MEDIA_ERR_SUBOPTIMAL' or something?

    When the user agent has completely fetched of the entire media resource, it must move on to the next step. This might never happen, e.g. when streaming an infinite resource such as Web radio.

  4. If the fetching process completes without errors, then set the networkState attribute to NETWORK_LOADED, and queue a task to fire a progress event called load at the element.

  5. Then, abort the overall resource selection algorithm.

If a media element whose networkState has the value NETWORK_EMPTY is inserted into a document, the user agent must invoke the media element's resource selection algorithm.

The autobuffer attribute is a boolean attribute. Its presence hints to the user agent that the author believes that the media element will likely be used, even though the element does not have an autoplay attribute. (The attribute has no effect if used in conjunction with the autoplay attribute, though including both is not an error.) This attribute may be ignored altogether. The attribute must be ignored if the autoplay attribute is present.

The autobuffer DOM attribute must reflect the content attribute of the same name.

media . buffered

Returns a TimeRanges object that represents the ranges of the media resource that the user agent has buffered.

The buffered attribute must return a new static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent has buffered, at the time the attribute is evaluated. Users agents must accurately determine the ranges available, even for media streams where this can only be determined by tedious inspection.

Typically this will be a single range anchored at the zero point, but if, e.g. the user agent uses HTTP range requests in response to seeking, then there could be multiple ranges.

User agents may discard previously buffered data.

Thus, a time position included within a range of the objects return by the buffered attribute at one time can end up being not included in the range(s) of objects returned by the same attribute at later times.

4.8.10.6 Offsets into the media resource
media . duration

Returns the length of the media resource, in seconds.

Returns NaN if the duration isn't available.

Returns Infinity for unbounded streams.

media . currentTime [ = value ]

Returns the current playback position, in seconds.

Can be set, to seek to the given time.

Will throw an INVALID_STATE_ERR exception if there is no selected media resource. Will throw an INDEX_SIZE_ERR exception if the given time is not within the ranges to which the user agent can seek.

media . startTime

Returns the earliest possible position, in seconds. This is the time for the start of the current clip. It might not be zero if the clip's timeline is not zero-based, or if the resource is a streaming resource (in which case it gives the earliest time that the user agent is able to seek back to).

The duration attribute must return the length of the media resource, in seconds. If no media data is available, then the attributes must return the Not-a-Number (NaN) value. If the media resource is known to be unbounded (e.g. a streaming radio), then the attribute must return the positive Infinity value.

The user agent must determine the duration of the media resource before playing any part of the media data and before setting readyState to a value equal to or greater than HAVE_METADATA, even if doing so requires seeking to multiple parts of the resource.

When the length of the media resource changes (e.g. from being unknown to known, or from a previously established length to a new length) the user agent must queue a task to fire a simple event called durationchange at the media element.

If an "infinite" stream ends for some reason, then the duration would change from positive Infinity to the time of the last frame or sample in the stream, and the durationchange event would be fired. Similarly, if the user agent initially estimated the media resource's duration instead of determining it precisely, and later revises the estimate based on new information, then the duration would change and the durationchange event would be fired.

Media elements have a current playback position, which must initially be zero. The current position is a time.

The currentTime attribute must, on getting, return the current playback position, expressed in seconds. On setting, the user agent must seek to the new value (which might raise an exception).

If the media resource is a streaming resource, then the user agent might be unable to obtain certain parts of the resource after it has expired from its buffer. Similarly, some media resources might have a timeline that doesn't start at zero. The earliest possible position is the earliest position in the stream or resource that the user agent can ever obtain again.

The startTime attribute must, on getting, return the earliest possible position, expressed in seconds.

When the earliest possible position changes, then: if the current playback position is before the earliest possible position, the user agent must seek to the earliest possible position; otherwise, if the user agent has not fired a timeupdate event at the element in the past 15 to 250ms, then the user agent must queue a task to fire a simple event called timeupdate at the element.

The loop attribute is a boolean attribute that, if specified, indicates that the media element is to seek back to the start of the media resource upon reaching the end.

The loop DOM attribute must reflect the content attribute of the same name.

4.8.10.7 The ready states
media . readyState

Returns a value that expresses the current state of the element with respect to rendering the current playback position, from the codes in the list below.

Media elements have a ready state, which describes to what degree they are ready to be rendered at the current playback position. The possible values are as follows; the ready state of a media element at any particular time is the greatest value describing the state of the element:

HAVE_NOTHING (numeric value 0)
No information regarding the media resource is available. No data for the current playback position is available. Media elements whose networkState attribute is NETWORK_EMPTY are always in the HAVE_NOTHING state.
HAVE_METADATA (numeric value 1)
Enough of the resource has been obtained that the duration of the resource is available. In the case of a video element, the dimensions of the video are also available. The API will no longer raise an exception when seeking. No media data is available for the immediate current playback position.
HAVE_CURRENT_DATA (numeric value 2)
Data for the immediate current playback position is available, but either not enough data is available that the user agent could successfully advance the current playback position in the direction of playback at all without immediately reverting to the HAVE_METADATA state, or there is no more data to obtain in the direction of playback. For example, in video this corresponds to the user agent having data from the current frame, but not the next frame; and to when playback has ended.
HAVE_FUTURE_DATA (numeric value 3)
Data for the immediate current playback position is available, as well as enough data for the user agent to advance the current playback position in the direction of playback at least a little without immediately reverting to the HAVE_METADATA state. For example, in video this corresponds to the user agent having data for at least the current frame and the next frame. The user agent cannot be in this state if playback has ended, as the current playback position can never advanced in this case.
HAVE_ENOUGH_DATA (numeric value 4)
All the conditions described for the HAVE_FUTURE_DATA state are met, and, in addition, the user agent estimates that data is being fetched at a rate where the current playback position, if it were to advance at the rate given by the defaultPlaybackRate attribute, would not overtake the available data before playback reaches the end of the media resource.

When the ready state of a media element whose networkState is not NETWORK_EMPTY changes, the user agent must follow the steps given below:

If the previous ready state was HAVE_NOTHING, and the new ready state is HAVE_METADATA

A loadedmetadata DOM event will be fired as part of the load() algorithm.

If the previous ready state was HAVE_METADATA and the new ready state is HAVE_CURRENT_DATA or greater

If this is the first time this occurs for this media element since the load() algorithm was last invoked, the user agent must queue a task to fire a simple event called loadeddata at the element.

If the new ready state is HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA, then the relevant steps below must then be run also.

If the previous ready state was HAVE_FUTURE_DATA or more, and the new ready state is HAVE_CURRENT_DATA or less

A waiting DOM event can be fired, depending on the current state of playback.

If the previous ready state was HAVE_CURRENT_DATA or less, and the new ready state is HAVE_FUTURE_DATA

The user agent must queue a task to fire a simple event called canplay.

If the element is potentially playing, the user agent must queue a task to fire a simple event called playing.

If the new ready state is HAVE_ENOUGH_DATA

If the previous ready state was HAVE_CURRENT_DATA or less, the user agent must queue a task to fire a simple event called canplay, and, if the element is also potentially playing, queue a task to fire a simple event called playing.

If the autoplaying flag is true, and the paused attribute is true, and the media element has an autoplay attribute specified, then the user agent may also set the paused attribute to false, queue a task to fire a simple event called play, and queue a task to fire a simple event called playing.

User agents are not required to autoplay, and it is suggested that user agents honor user preferences on the matter. Authors are urged to use the autoplay attribute rather than using script to force the video to play, so as to allow the user to override the behavior if so desired.

In any case, the user agent must finally queue a task to fire a simple event called canplaythrough.

It is possible for the ready state of a media element to jump between these states discontinuously. For example, the state of a media element can jump straight from HAVE_METADATA to HAVE_ENOUGH_DATA without passing through the HAVE_CURRENT_DATA and HAVE_FUTURE_DATA states.

The readyState DOM attribute must, on getting, return the value described above that describes the current ready state of the media element.

The autoplay attribute is a boolean attribute. When present, the user agent (as described in the algorithm described herein) will automatically begin playback of the media resource as soon as it can do so without stopping.

The autoplay DOM attribute must reflect the content attribute of the same name.

4.8.10.8 Cue ranges
media . addCueRange(className, id, start, end, pauseOnExit, enterCallback, exitCallback)

Registers a range of time, given in seconds, and a pair of callbacks, the first of which will be invoked when the current playback position enters the range, and the second of which will be invoked when it exits the range. The callbacks are invoked with the given ID as their argument.

In addition, if the pauseOnExit argument is true, then playback will pause when it reaches the end of the range.

media . removeCueRange(className)

Removes all the ranges that were registered with the given class name.

Media elements have a set of cue ranges. Each cue range is made up of the following information:

A class name
A group of related ranges can be given the same class name so that they can all be removed at the same time.
An identifier
A string can be assigned to each cue range for identification by script. The string need not be unique and can contain any value.
A start time
An end time
The actual time range, using the same timeline as the media resource itself.
A "pause" boolean
A flag indicating whether to pause playback on exit.
An "enter" callback
A callback that is called when the current playback position enters the range.
An "exit" callback
A callback that is called when the current playback position exits the range.
An "active" boolean
A flag indicating whether the range is active or not.

The addCueRange(className, id, start, end, pauseOnExit, enterCallback, exitCallback) method must, when called, add a cue range to the media element, that cue range having the class name className, the identifier id, the start time start (in seconds), the end time end (in seconds), the "pause" boolean with the same value as pauseOnExit, the "enter" callback enterCallback, the "exit" callback exitCallback, and an "active" boolean that is true if the current playback position is equal to or greater than the start time and less than the end time, and false otherwise.

The removeCueRanges(className) method must, when called, remove all the cue ranges of the media element which have the class name className.

4.8.10.9 Playing the media resource
media . paused

Returns true if playback is paused; false otherwise.

media . ended

Returns true if playback has reached the end of the media resource.

media . defaultPlaybackRate [ = value ]

Returns the default rate of playback, for when the user is not fast-forwarding or reversing through the media resource.

Can be set, to change the default rate of playback.

The default rate has no direct effect on playback, but if the user switches to a fast-forward mode, when they return to the normal playback mode, it is expected that the rate of playback will be returned to the default rate of playback.

media . playbackRate [ = value ]

Returns the current rate playback, where 1.0 is normal speed.

Can be set, to change the rate of playback.

media . played

Returns a TimeRanges object that represents the ranges of the media resource that the user agent has played.

media . play()

Sets the paused attribute to false, loading the media resource and beginning playback if necessary. If the playback had ended, will restart it from the start.

media . pause()

Sets the paused attribute to true, loading the media resource if necessary.

The paused attribute represents whether the media element is paused or not. The attribute must initially be true.

A media element is said to be potentially playing when its paused attribute is false, the readyState attribute is either HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA, the element has not ended playback, playback has not stopped due to errors, and the element has not paused for user interaction.

A media element is said to have ended playback when the element's readyState attribute is HAVE_METADATA or greater, and either the current playback position is the end of the media resource and the direction of playback is forwards and the media element does not have a loop attribute specified, or the current playback position is the earliest possible position and the direction of playback is backwards.

The ended attribute must return true if the media element has ended playback and the direction of playback is forwards, and false otherwise.

A media element is said to have stopped due to errors when the element's readyState attribute is HAVE_METADATA or greater, and the user agent encounters a non-fatal error during the processing of the media data, and due to that error, is not able to play the content at the current playback position.

A media element is said to have paused for user interaction when its paused attribute is false, the readyState attribute is either HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA and the user agent has reached a point in the media resource where the user has to make a selection for the resource to continue.

It is possible for a media element to have both ended playback and paused for user interaction at the same time.

When a media element that is potentially playing stops playing because it has paused for user interaction, the user agent must queue a task to fire a simple event called timeupdate at the element.

When a media element that is potentially playing stops playing because its readyState attribute changes to a value lower than HAVE_FUTURE_DATA, without the element having ended playback, or playback having stopped due to errors, or playback having paused for user interaction, or the seeking algorithm being invoked, the user agent must queue a task to fire a simple event called timeupdate at the element, and queue a task to fire a simple event called waiting at the element.

When the current playback position reaches the end of the media resource when the direction of playback is forwards, then the user agent must follow these steps:

  1. If the media element has a loop attribute specified, then seek to the earliest possible position of the media resource and abort these steps.

  2. Stop playback.

    The ended attribute becomes true.

  3. The user agent must queue a task to fire a simple event called timeupdate at the element.

  4. The user agent must queue a task to fire a simple event called ended at the element.

When the current playback position reaches the earliest possible position of the media resource when the direction of playback is backwards, then the user agent must follow these steps:

  1. Stop playback.

  2. The user agent must queue a task to fire a simple event called timeupdate at the element.

The defaultPlaybackRate attribute gives the desired speed at which the media resource is to play, as a multiple of its intrinsic speed. The attribute is mutable: on getting it must return the last value it was set to, or 1.0 if it hasn't yet been set; on setting the attribute must be set to the new value.

The playbackRate attribute gives the speed at which the media resource plays, as a multiple of its intrinsic speed. If it is not equal to the defaultPlaybackRate, then the implication is that the user is using a feature such as fast forward or slow motion playback. The attribute is mutable: on getting it must return the last value it was set to, or 1.0 if it hasn't yet been set; on setting the attribute must be set to the new value, and the playback must change speed (if the element is potentially playing).

If the playbackRate is positive or zero, then the direction of playback is forwards. Otherwise, it is backwards.

The "play" function in a user agent's interface must set the playbackRate attribute to the value of the defaultPlaybackRate attribute before invoking the play() method's steps. Features such as fast-forward or rewind must be implemented by only changing the playbackRate attribute.

When the defaultPlaybackRate or playbackRate attributes change value (either by being set by script or by being changed directly by the user agent, e.g. in response to user control) the user agent must queue a task to fire a simple event called ratechange at the media element.

The played attribute must return a new static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent has so far rendered, at the time the attribute is evaluated.


When the play() method on a media element is invoked, the user agent must run the following steps.

  1. If the media element's networkState attribute has the value NETWORK_EMPTY, then the user agent must invoke the media element's resource selection algorithm.

  2. If the playback has ended, then the user agent must seek to the earliest possible position of the media resource.

    This will cause the user agent to queue a task to fire a simple event called timeupdate at the media element.

  3. If the media element's paused attribute is true, it must be set to false.

    If this changed the value of paused, the user agent must run the following substeps:

    1. Queue a task to fire a simple event called play at the element.

    2. If the media element's readyState attribute has the value HAVE_NOTHING, HAVE_METADATA, or HAVE_CURRENT_DATA, queue a task to fire a simple event called waiting at the element.

    3. Otherwise, the media element's readyState attribute has the value HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA; queue a task to fire a simple event called playing at the element.

  4. The media element's autoplaying flag must be set to false.

  5. The method must then return.


When the pause() method is invoked, the user agent must run the following steps:

  1. If the media element's networkState attribute has the value NETWORK_EMPTY, then the user agent must invoke the media element's resource selection algorithm.

  2. If the media element's paused attribute is false, it must be set to true.

  3. The media element's autoplaying flag must be set to false.

  4. If the second step above changed the value of paused, then the user agent must queue a task to fire a simple event called timeupdate at the element, and queue a task to fire a simple event called pause at the element.


When a media element is potentially playing and its Document is an active document, its current playback position must increase monotonically at playbackRate units of media time per unit time of wall clock time.

This specification doesn't define how the user agent achieves the appropriate playback rate — depending on the protocol and media available, it is plausible that the user agent could negotiate with the server to have the server provide the media data at the appropriate rate, so that (except for the period between when the rate is changed and when the server updates the stream's playback rate) the client doesn't actually have to drop or interpolate any frames.

When the playbackRate is negative (playback is backwards), any corresponding audio must be muted. When the playbackRate is so low or so high that the user agent cannot play audio usefully, the corresponding audio must also be muted. If the playbackRate is not 1.0, the user agent may apply pitch adjustments to the audio as necessary to render it faithfully.

The playbackRate can be 0.0, in which case the current playback position doesn't move, despite playback not being paused (paused doesn't become true, and the pause event doesn't fire).

Media elements that are potentially playing while not in a Document must not play any video, but should play any audio component. Media elements must not stop playing just because all references to them have been removed; only once a media element to which no references exist has reached a point where no further audio remains to be played for that element (e.g. because the element is paused, or because the end of the clip has been reached, or because its playbackRate is 0.0) may the element be garbage collected.


When the current playback position of a media element changes (e.g. due to playback or seeking), the user agent must run the following steps. If the current playback position changes while the steps are running, then the user agent must wait for the steps to complete, and then must immediately rerun the steps. (These steps are thus run as often as possible or needed — if one iteration takes a long time, this can cause certain ranges to be skipped over as the user agent rushes ahead to "catch up".)

  1. Let current ranges be an ordered list of cue ranges, initialized to contain all the cue ranges of the media element whose start times are less than or equal to the current playback position and whose end times are greater than the current playback position, in the order they were added to the element.

  2. Let other ranges be an ordered list of cue ranges, initialized to contain all the cue ranges of the media element that are not present in current ranges, in the order they were added to the element.

  3. If the time was reached through the usual monotonic increase of the current playback position during normal playback, and if the user agent has not fired a timeupdate event at the element in the past 15 to 250ms, then the user agent must queue a task to fire a simple event called timeupdate at the element. (In the other cases, such as explicit seeks, relevant events get fired as part of the overall process of changing the current playback position.)

    The event thus is not to be fired faster than about 66Hz or slower than 4Hz. User agents are encouraged to vary the frequency of the event based on the system load and the average cost of processing the event each time, so that the UI updates are not any more frequent than the user agent can comfortably handle while decoding the video.

  4. If none of the cue ranges in current ranges have their "active" boolean set to "false" (inactive) and none of the cue ranges in other ranges have their "active" boolean set to "true" (active), then abort these steps.

  5. If the time was reached through the usual monotonic increase of the current playback position during normal playback, and there are cue ranges in other ranges that have both their "active" boolean and their "pause" boolean set to "true", then immediately act as if the element's pause() method had been invoked. (In the other cases, such as explicit seeks, playback is not paused by exiting a cue range, even if that cue range has its "pause" boolean set to "true".)

  6. For each non-null "exit" callback of the cue ranges in other ranges that have their "active" boolean set to "true" (active), in list order, queue a task that invokes the callback, passing the cue range's identifier as the callback's only argument.

  7. For each non-null "enter" callback of the cue ranges in current ranges that have their "active" boolean set to "false" (inactive), in list order, queue a task that invokes the callback, passing the cue range's identifier as the callback's only argument.

  8. Set the "active" boolean of all the cue ranges in the current ranges list to "true" (active), and the "active" boolean of all the cue ranges in the other ranges list to "false" (inactive).

When a media element is removed from a Document, if the media element's networkState attribute has a value other than NETWORK_EMPTY then the user agent must act as if the pause() method had been invoked.

If the media element's Document stops being a fully active document, then the playback will stop until the document is active again.

4.8.10.10 Seeking
media . seeking

Returns true if the user agent is currently seeking.

media . seekable

Returns a TimeRanges object that represents the ranges of the media resource to which it is possible for the user agent to seek.

The seeking attribute must initially have the value false.

When the user agent is required to seek to a particular new playback position in the media resource, it means that the user agent must run the following steps:

  1. If the media element's readyState is HAVE_NOTHING, then the user agent must raise an INVALID_STATE_ERR exception (if the seek was in response to a DOM method call or setting of a DOM attribute), and abort these steps.

  2. If the new playback position is later than the end of the media resource, then let it be the end of the media resource instead.

  3. If the new playback position is less than the earliest possible position, let it be that position instead.

  4. If the (possibly now changed) new playback position is not in one of the ranges given in the seekable attribute, then the user agent must raise an INDEX_SIZE_ERR exception (if the seek was in response to a DOM method call or setting of a DOM attribute), and abort these steps.

  5. The current playback position must be set to the given new playback position.

  6. The seeking DOM attribute must be set to true.

  7. The user agent must queue a task to fire a simple event called timeupdate at the element.

  8. If the media element was potentially playing immediately before it started seeking, but seeking caused its readyState attribute to change to a value lower than HAVE_FUTURE_DATA, the user agent must queue a task to fire a simple event called waiting at the element.

  9. If, when it reaches this step, the user agent has still not established whether or not the media data for the new playback position is available, and, if it is, decoded enough data to play back that position, the user agent must queue a task to fire a simple event called seeking at the element.

  10. If the seek was in response to a DOM method call or setting of a DOM attribute, then continue the script. The remainder of these steps must be run asynchronously.

  11. The user agent must wait until it has established whether or not the media data for the new playback position is available, and, if it is, until it has decoded enough data to play back that position.

  12. The seeking DOM attribute must be set to false.

  13. The user agent must queue a task to fire a simple event called seeked at the element.

The seekable attribute must return a new static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent is able to seek to, at the time the attribute is evaluated.

If the user agent can seek to anywhere in the media resource, e.g. because it a simple movie file and the user agent and the server support HTTP Range requests, then the attribute would return an object with one range, whose start is the time of the first frame (typically zero), and whose end is the same as the time of the first frame plus the duration attribute's value (which would equal the time of the last frame).

The range might be continuously changing, e.g. if the user agent is buffering a sliding window on an infinite stream. This is the behavior seen with DVRs viewing live TV, for instance.

Media resources might be internally scripted or interactive. Thus, a media element could play in a non-linear fashion. If this happens, the user agent must act as if the algorithm for seeking was used whenever the current playback position changes in a discontinuous fashion (so that the relevant events fire).

4.8.10.11 User interface

The controls attribute is a boolean attribute. If present, it indicates that the author has not provided a scripted controller and would like the user agent to provide its own set of controls.

If the attribute is present, or if scripting is disabled for the media element, then the user agent should expose a user interface to the user. This user interface should include features to begin playback, pause playback, seek to an arbitrary position in the content (if the content supports arbitrary seeking), change the volume, and show the media content in manners more suitable to the user (e.g. full-screen video or in an independent resizable window). Other controls may also be made available.

If the attribute is absent, then the user agent should avoid making a user interface available that could conflict with an author-provided user interface. User agents may make the following features available, however, even when the attribute is absent:

User agents may provide controls to affect playback of the media resource (e.g. play, pause, seeking, and volume controls), but such features should not interfere with the page's normal rendering. For example, such features could be exposed in the media element's context menu.

Where possible (specifically, for starting, stopping, pausing, and unpausing playback, for muting or changing the volume of the audio, and for seeking), user interface features exposed by the user agent must be implemented in terms of the DOM API described above, so that, e.g., all the same events fire.

The controls DOM attribute must reflect the content attribute of the same name.


media . volume [ = value ]

Returns the current playback volume, as a number in the range 0.0 to 1.0, where 0.0 is the quietest and 1.0 the loudest.

Can be set, to change the volume.

Throws an INDEX_SIZE_ERR if the new value is not in the range 0.0 .. 1.0.

media . muted [ = value ]

Returns true if audio is muted, overriding the volume attribute, and false if the volume attribute is being honored.

Can be set, to change whether the audio is muted or not.

The volume attribute must return the playback volume of any audio portions of the media element, in the range 0.0 (silent) to 1.0 (loudest). Initially, the volume must be 1.0, but user agents may remember the last set value across sessions, on a per-site basis or otherwise, so the volume may start at other values. On setting, if the new value is in the range 0.0 to 1.0 inclusive, the attribute must be set to the new value and the playback volume must be correspondingly adjusted as soon as possible after setting the attribute, with 0.0 being silent, and 1.0 being the loudest setting, values in between increasing in loudness. The range need not be linear. The loudest setting may be lower than the system's loudest possible setting; for example the user could have set a maximum volume. If the new value is outside the range 0.0 to 1.0 inclusive, then, on setting, an INDEX_SIZE_ERR exception must be raised instead.

The muted attribute must return true if the audio channels are muted and false otherwise. Initially, the audio channels should not be muted (false), but user agents may remember the last set value across sessions, on a per-site basis or otherwise, so the muted state may start as muted (true). On setting, the attribute must be set to the new value; if the new value is true, audio playback for this media resource must then be muted, and if false, audio playback must then be enabled.

Whenever either the muted or volume attributes are changed, the user agent must queue a task to fire a simple event called volumechange at the media element.

4.8.10.12 Time ranges

Objects implementing the TimeRanges interface represent a list of ranges (periods) of time.

interface TimeRanges {
  readonly attribute unsigned long length;
  float start(in unsigned long index);
  float end(in unsigned long index);
};
media . length

Returns the number of ranges in the object.

time = media . start(index)

Returns the time for the start of the range with the given index.

Throws an INDEX_SIZE_ERR if the index is out of range.

time = media . end(index)

Returns the time for the end of the range with the given index.

Throws an INDEX_SIZE_ERR if the index is out of range.

The length DOM attribute must return the number of ranges represented by the object.

The start(index) method must return the position of the start of the indexth range represented by the object, in seconds measured from the start of the timeline that the object covers.

The end(index) method must return the position of the end of the indexth range represented by the object, in seconds measured from the start of the timeline that the object covers.

These methods must raise INDEX_SIZE_ERR exceptions if called with an index argument greater than or equal to the number of ranges represented by the object.

When a TimeRanges object is said to be a normalized TimeRanges object, the ranges it represents must obey the following criteria:

In other words, the ranges in such an object are ordered, don't overlap, aren't empty, and don't touch (adjacent ranges are folded into one bigger range).

The timelines used by the objects returned by the buffered, seekable and played DOM attributes of media elements must be the same as that element's media resource's timeline.

4.8.10.13 Event summary

The following events fire on media elements as part of the processing model described above:

Event name Interface Dispatched when... Preconditions
loadstart ProgressEvent [PROGRESS] The user agent begins looking for media data, as part of the resource selection algorithm. networkState equals NETWORK_LOADING
progress ProgressEvent [PROGRESS] The user agent is fetching media data. networkState equals NETWORK_LOADING
suspend ProgressEvent [PROGRESS] The user agent is intentionally not currently fetching media data, but does not have the entire media resource downloaded. networkState equals NETWORK_IDLE
load ProgressEvent [PROGRESS] The user agent finishes fetching the entire media resource. networkState equals NETWORK_LOADED
abort ProgressEvent [PROGRESS] The user agent stops fetching the media data before it is completely downloaded. error is an object with the code MEDIA_ERR_ABORTED. networkState equals either NETWORK_EMPTY or NETWORK_LOADED, depending on when the download was aborted.
error ProgressEvent [PROGRESS] An error occurs while fetching the media data. error is an object with the code MEDIA_ERR_NETWORK or higher. networkState equals either NETWORK_EMPTY or NETWORK_LOADED, depending on when the download was aborted.
emptied Event A media element whose networkState was previously not in the NETWORK_EMPTY state has just switched to that state (either because of a fatal error during load that's about to be reported, or because the load() method was invoked while the resource selection algorithm was already running, in which case it is fired synchronously during the load() method call). networkState is NETWORK_EMPTY; all the DOM attributes are in their initial states.
stalled ProgressEvent The user agent is trying to fetch media data, but data is unexpectedly not forthcoming. networkState is NETWORK_LOADING.
play Event Playback has begun. Fired after the play() method has returned. paused is newly false.
pause Event Playback has been paused. Fired after the pause method has returned. paused is newly true.
loadedmetadata Event The user agent has just determined the duration and dimensions of the media resource. readyState is newly equal to HAVE_METADATA or greater for the first time.
loadeddata Event The user agent can render the media data at the current playback position for the first time. readyState newly increased to HAVE_CURRENT_DATA or greater for the first time.
waiting Event Playback has stopped because the next frame is not available, but the user agent expects that frame to become available in due course. readyState is newly equal to or less than HAVE_CURRENT_DATA, and paused is false. Either seeking is true, or the current playback position is not contained in any of the ranges in buffered. It is possible for playback to stop for two other reasons without paused being false, but those two reasons do not fire this event: maybe playback ended, or playback stopped due to errors.
playing Event Playback has started. readyState is newly equal to or greater than HAVE_FUTURE_DATA, paused is false, seeking is false, or the current playback position is contained in one of the ranges in buffered.
canplay Event The user agent can resume playback of the media data, but estimates that if playback were to be started now, the media resource could not be rendered at the current playback rate up to its end without having to stop for further buffering of content. readyState newly increased to HAVE_FUTURE_DATA or greater.
canplaythrough Event The user agent estimates that if playback were to be started now, the media resource could be rendered at the current playback rate all the way to its end without having to stop for further buffering. readyState is newly equal to HAVE_ENOUGH_DATA.
seeking Event The seeking DOM attribute changed to true and the seek operation is taking long enough that the user agent has time to fire the event.
seeked Event The seeking DOM attribute changed to false.
timeupdate Event The current playback position changed as part of normal playback or in an especially interesting way, for example discontinuously.
ended Event Playback has stopped because the end of the media resource was reached. currentTime equals the end of the media resource; ended is true.
ratechange Event Either the defaultPlaybackRate or the playbackRate attribute has just been updated.
durationchange Event The duration attribute has just been updated.
volumechange Event Either the volume attribute or the muted attribute has changed. Fired after the relevant attribute's setter has returned.
4.8.10.14 Security and privacy considerations

The main security and privacy implications of the video and audio elements come from the ability to embed media cross-origin. There are two directions that threats can flow: from hostile content to a victim page, and from a hostile page to victim content.


If a victim page embeds hostile content, the threat is that the content might contain scripted code that attempts to interact with the Document that embeds the content. To avoid this, user agents must ensure that there is no access from the content to the embedding page. In the case of media content that uses DOM concepts, the embedded content must be treated as if it was in its own unrelated top-level browsing context.

For instance, if an SVG animation was embedded in a video element, the user agent would not give it access to the DOM of the outer page. From the perspective of scripts in the SVG resource, the SVG file would appear to be in a lone top-level browsing context with no parent.


If a hostile page embeds victim content, the threat is that the embedding page could obtain information from the content that it would not otherwise have access to. The API does expose some information: the existence of the media, its type, its duration, its size, and the performance characteristics of its host. Such information is already potentially problematic, but in practice the same information can more or less be obtained using the img element, and so it has been deemed acceptable.

However, significantly more sensitive information could be obtained if the user agent further exposes metadata within the content such as subtitles or chapter titles. This version of the API does not expose such information. Future extensions to this API will likely reuse a mechanism such as CORS to check that the embedded content's site has opted in to exposing such information. [CORS]

An attacker could trick a user running within a corporate network into visiting a site that attempts to load a video from a previously leaked location on the corporation's intranet. If such a video included confidential plans for a new product, then being able to read the subtitles would present a confidentiality breach.

4.8.11 The canvas element

Categories
Flow content.
Phrasing content.
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Transparent.
Content attributes:
Global attributes
width
height
DOM interface:
interface HTMLCanvasElement : HTMLElement {
           attribute unsigned long width;
           attribute unsigned long height;

  DOMString toDataURL([Optional] in DOMString type, [Variadic] in any args);

  Object getContext(in DOMString contextId);
};

The canvas element represents a resolution-dependent bitmap canvas, which can be used for rendering graphs, game graphics, or other visual images on the fly.

Authors should not use the canvas element in a document when a more suitable element is available. For example, it is inappropriate to use a canvas element to render a page heading: if the desired presentation of the heading is graphically intense, it should be marked up using appropriate elements (typically h1) and then styled using CSS and supporting technologies such as XBL.

When authors use the canvas element, they must also provide content that, when presented to the user, conveys essentially the same function or purpose as the bitmap canvas. This content may be placed as content of the canvas element. The contents of the canvas element, if any, are the element's fallback content.

In interactive visual media, if scripting is enabled for the canvas element, the canvas element represents an embedded element with a dynamically created image.

In non-interactive, static, visual media, if the canvas element has been previously painted on (e.g. if the page was viewed in an interactive visual medium and is now being printed, or if some script that ran during the page layout process painted on the element), then the canvas element represents embedded content with the current image and size. Otherwise, the element represents its fallback content instead.

In non-visual media, and in visual media if scripting is disabled for the canvas element, the canvas element represents its fallback content instead.

The canvas element has two attributes to control the size of the coordinate space: width and height. These attributes, when specified, must have values that are valid non-negative integers. The rules for parsing non-negative integers must be used to obtain their numeric values. If an attribute is missing, or if parsing its value returns an error, then the default value must be used instead. The width attribute defaults to 300, and the height attribute defaults to 150.

The intrinsic dimensions of the canvas element equal the size of the coordinate space, with the numbers interpreted in CSS pixels. However, the element can be sized arbitrarily by a style sheet. During rendering, the image is scaled to fit this layout size.

The size of the coordinate space does not necessarily represent the size of the actual bitmap that the user agent will use internally or during rendering. On high-definition displays, for instance, the user agent may internally use a bitmap with two device pixels per unit in the coordinate space, so that the rendering remains at high quality throughout.

Whenever the width and height attributes are set (whether to a new value or to the previous value), the bitmap and any associated contexts must be cleared back to their initial state and reinitialized with the newly specified coordinate space dimensions.

The width and height DOM attributes must reflect the respective content attributes of the same name.

Only one square appears to be drawn in the following example:

  // canvas is a reference to a <canvas> element
  var context = canvas.getContext('2d');
  context.fillRect(0,0,50,50);
  canvas.setAttribute('width', '300'); // clears the canvas
  context.fillRect(0,100,50,50);
  canvas.width = canvas.width; // clears the canvas
  context.fillRect(100,0,50,50); // only this square remains

When the canvas is initialized it must be set to fully transparent black.

To draw on the canvas, authors must first obtain a reference to a context using the getContext(contextId) method of the canvas element.

context = canvas . getContext(contextId)

Returns an object that exposes an API for drawing on the canvas.

Returns null if the given context ID is not supported.

This specification only defines one context, with the name "2d". If getContext() is called with that exact string for its contextId argument, then the UA must return a reference to an object implementing CanvasRenderingContext2D. Other specifications may define their own contexts, which would return different objects.

Vendors may also define experimental contexts using the syntax vendorname-context, for example, moz-3d.

When the UA is passed an empty string or a string specifying a context that it does not support, then it must return null. String comparisons must be case-sensitive.

A future version of this specification will probably define a 3d context (probably based on the OpenGL ES API).


url = canvas . toDataURL( [ type, ... ])

Returns a data: URL for the image in the canvas.

The first argument, if provided, controls the type of the image to be returned (e.g. PNG or JPEG). The default is image/png; that type is also used if the given type isn't supported. The other arguments are specific to the type, and control the way that the image is generated, as given in the table below.

The toDataURL() method must, when called with no arguments, return a data: URL containing a representation of the image as a PNG file. [PNG].

If the canvas has no pixels (i.e. either its horizontal dimension or its vertical dimension is zero) then the method must return the string "data:,". (This is the shortest data: URL; it represents the empty string in a text/plain resource.)

When the toDataURL(type) method, when called with one or more arguments, must return a data: URL containing a representation of the image in the format given by type. The possible values are MIME types with no parameters, for example image/png, image/jpeg, or even maybe image/svg+xml if the implementation actually keeps enough information to reliably render an SVG image from the canvas.

For image types that do not support an alpha channel, the image must be composited onto a solid black background using the source-over operator, and the resulting image must be the one used to create the data: URL.

Only support for image/png is required. User agents may support other types. If the user agent does not support the requested type, it must return the image using the PNG format.

User agents must convert the provided type to lower case before establishing if they support that type and before creating the data: URL.

When trying to use types other than image/png, authors can check if the image was really returned in the requested format by checking to see if the returned string starts with one the exact strings "data:image/png," or "data:image/png;". If it does, the image is PNG, and thus the requested type was not supported. (The one exception to this is if the canvas has either no height or no width, in which case the result might simply be "data:,".)

If the method is invoked with the first argument giving a type corresponding to one of the types given in the first column of the following table, and the user agent supports that type, then the subsequent arguments, if any, must be treated as described in the second cell of that row.

Type Other arguments
image/jpeg The second argument, if it is a number between 0.0 and 1.0, must be treated as the desired quality level. If it is not a number or is outside that range, the user agent must use its default value, as if the argument had been omitted.

Other arguments must be ignored and must not cause the user agent to raise an exception. A future version of this specification will probably define other parameters to be passed to toDataURL() to allow authors to more carefully control compression settings, image metadata, etc.

4.8.11.1 The 2D context

When the getContext() method of a canvas element is invoked with 2d as the argument, a CanvasRenderingContext2D object is returned.

There is only one CanvasRenderingContext2D object per canvas, so calling the getContext() method with the 2d argument a second time must return the same object.

The 2D context represents a flat Cartesian surface whose origin (0,0) is at the top left corner, with the coordinate space having x values increasing when going right, and y values increasing when going down.

interface CanvasRenderingContext2D {

  // back-reference to the canvas
  readonly attribute HTMLCanvasElement canvas;

  // state
  void save(); // push state on state stack
  void restore(); // pop state stack and restore state

  // transformations (default transform is the identity matrix)
  void scale(in float x, in float y);
  void rotate(in float angle);
  void translate(in float x, in float y);
  void transform(in float m11, in float m12, in float m21, in float m22, in float dx, in float dy);
  void setTransform(in float m11, in float m12, in float m21, in float m22, in float dx, in float dy);

  // compositing
           attribute float globalAlpha; // (default 1.0)
           attribute DOMString globalCompositeOperation; // (default source-over)

  // colors and styles
           attribute any strokeStyle; // (default black)
           attribute any fillStyle; // (default black)
  CanvasGradient createLinearGradient(in float x0, in float y0, in float x1, in float y1);
  CanvasGradient createRadialGradient(in float x0, in float y0, in float r0, in float x1, in float y1, in float r1);
  CanvasPattern createPattern(in HTMLImageElement image, in DOMString repetition);
  CanvasPattern createPattern(in HTMLCanvasElement image, in DOMString repetition);
  CanvasPattern createPattern(in HTMLVideoElement image, in DOMString repetition);

  // line caps/joins
           attribute float lineWidth; // (default 1)
           attribute DOMString lineCap; // "butt", "round", "square" (default "butt")
           attribute DOMString lineJoin; // "round", "bevel", "miter" (default "miter")
           attribute float miterLimit; // (default 10)

  // shadows
           attribute float shadowOffsetX; // (default 0)
           attribute float shadowOffsetY; // (default 0)
           attribute float shadowBlur; // (default 0)
           attribute DOMString shadowColor; // (default transparent black)

  // rects
  void clearRect(in float x, in float y, in float w, in float h);
  void fillRect(in float x, in float y, in float w, in float h);
  void strokeRect(in float x, in float y, in float w, in float h);

  // path API
  void beginPath();
  void closePath();
  void moveTo(in float x, in float y);
  void lineTo(in float x, in float y);
  void quadraticCurveTo(in float cpx, in float cpy, in float x, in float y);
  void bezierCurveTo(in float cp1x, in float cp1y, in float cp2x, in float cp2y, in float x, in float y);
  void arcTo(in float x1, in float y1, in float x2, in float y2, in float radius);
  void rect(in float x, in float y, in float w, in float h);
  void arc(in float x, in float y, in float radius, in float startAngle, in float endAngle, in boolean anticlockwise);
  void fill();
  void stroke();
  void clip();
  boolean isPointInPath(in float x, in float y);

  // text
           attribute DOMString font; // (default 10px sans-serif)
           attribute DOMString textAlign; // "start", "end", "left", "right", "center" (default: "start")
           attribute DOMString textBaseline; // "top", "hanging", "middle", "alphabetic", "ideographic", "bottom" (default: "alphabetic")
  void fillText(in DOMString text, in float x, in float y, [Optional] in float maxWidth);
  void strokeText(in DOMString text, in float x, in float y, [Optional] in float maxWidth);
  TextMetrics measureText(in DOMString text);

  // drawing images
  void drawImage(in HTMLImageElement image, in float dx, in float dy, [Optional] in float dw, in float dh);
  void drawImage(in HTMLImageElement image, in float sx, in float sy, in float sw, in float sh, in float dx, in float dy, in float dw, in float dh);
  void drawImage(in HTMLCanvasElement image, in float dx, in float dy, [Optional] in float dw, in float dh);
  void drawImage(in HTMLCanvasElement image, in float sx, in float sy, in float sw, in float sh, in float dx, in float dy, in float dw, in float dh);
  void drawImage(in HTMLVideoElement image, in float dx, in float dy, [Optional] in float dw, in float dh);
  void drawImage(in HTMLVideoElement image, in float sx, in float sy, in float sw, in float sh, in float dx, in float dy, in float dw, in float dh);

  // pixel manipulation
  ImageData createImageData(in float sw, in float sh);
  ImageData createImageData(in ImageData imagedata);
  ImageData getImageData(in float sx, in float sy, in float sw, in float sh);
  void putImageData(in ImageData imagedata, in float dx, in float dy, [Optional] in float dirtyX, in float dirtyY, in float dirtyWidth, in float dirtyHeight);
};

interface CanvasGradient {
  // opaque object
  void addColorStop(in float offset, in DOMString color);
};

interface CanvasPattern {
  // opaque object
};

interface TextMetrics {
  readonly attribute float width;
};

interface ImageData {
  readonly attribute unsigned long width;
  readonly attribute unsigned long height;
  readonly attribute CanvasPixelArray data;
};

[IndexGetter, IndexSetter]
interface CanvasPixelArray {
  readonly attribute unsigned long length;
};
context . canvas

Returns the canvas element.

The canvas attribute must return the canvas element that the context paints on.

Unless otherwise stated, for the 2D context interface, any method call with a numeric argument whose value is infinite or a NaN value must be ignored.

Whenever the CSS value currentColor is used as a color in this API, the "computed value of the 'color' property" for the purposes of determining the computed value of the currentColor keyword is the computed value of the 'color' property on the element in question at the time that the color is specified (e.g. when the appropriate attribute is set, or when the method is called; not when the color is rendered or otherwise used). If the computed value of the 'color' property is undefined for a particular case (e.g. because the element is not in a document), then the "computed value of the 'color' property" for the purposes of determining the computed value of the currentColor keyword is fully opaque black. [CSS3COLOR]

4.8.11.1.1 The canvas state

Each context maintains a stack of drawing states. Drawing states consist of:

The current path and the current bitmap are not part of the drawing state. The current path is persistent, and can only be reset using the beginPath() method. The current bitmap is a property of the canvas, not the context.

context . save()

Pushes the current state onto the stack.

context . restore()

Pops the top state on the stack, restoring the context to that state.

The save() method must push a copy of the current drawing state onto the drawing state stack.

The restore() method must pop the top entry in the drawing state stack, and reset the drawing state it describes. If there is no saved state, the method must do nothing.

4.8.11.1.2 Transformations

The transformation matrix is applied to coordinates when creating shapes and paths.

When the context is created, the transformation matrix must initially be the identity transform. It may then be adjusted using the transformation methods.

The transformations must be performed in reverse order. For instance, if a scale transformation that doubles the width is applied, followed by a rotation transformation that rotates drawing operations by a quarter turn, and a rectangle twice as wide as it is tall is then drawn on the canvas, the actual result will be a square.

context . scale(x, y)

Changes the transformation matrix to apply a scaling transformation with the given characteristics.

context . rotate(angle)

Changes the transformation matrix to apply a rotation transformation with the given characteristics.

context . translate(x, y)

Changes the transformation matrix to apply a translation transformation with the given characteristics.

context . transform(m11, m12, m21, m22, dx, dy)

Changes the transformation matrix to apply the matrix given by the arguments as described below.

context . setTransform(m11, m12, m21, m22, dx, dy)

Changes the transformation matrix to the matrix given by the arguments as described below.

The scale(x, y) method must add the scaling transformation described by the arguments to the transformation matrix. The x argument represents the scale factor in the horizontal direction and the y argument represents the scale factor in the vertical direction. The factors are multiples.

The rotate(angle) method must add the rotation transformation described by the argument to the transformation matrix. The angle argument represents a clockwise rotation angle expressed in radians.

The translate(x, y) method must add the translation transformation described by the arguments to the transformation matrix. The x argument represents the translation distance in the horizontal direction and the y argument represents the translation distance in the vertical direction. The arguments are in coordinate space units.

The transform(m11, m12, m21, m22, dx, dy) method must multiply the current transformation matrix with the matrix described by:

m11 m21 dx
m12 m22 dy
0 0 1

The setTransform(m11, m12, m21, m22, dx, dy) method must reset the current transform to the identity matrix, and then invoke the transform(m11, m12, m21, m22, dx, dy) method with the same arguments.

4.8.11.1.3 Compositing
context . globalAlpha [ = value ]

Returns the current alpha value applied to rendering operations.

Can be set, to change the alpha value. Values outside of the range 0.0 .. 1.0 are ignored.

context . globalCompositeOperation [ = value ]

Returns the current composition operation, from the list below.

Can be set, to change the composition operation. Unknown values are ignored.

All drawing operations are affected by the global compositing attributes, globalAlpha and globalCompositeOperation.

The globalAlpha attribute gives an alpha value that is applied to shapes and images before they are composited onto the canvas. The value must be in the range from 0.0 (fully transparent) to 1.0 (no additional transparency). If an attempt is made to set the attribute to a value outside this range, the attribute must retain its previous value. When the context is created, the globalAlpha attribute must initially have the value 1.0.

The globalCompositeOperation attribute sets how shapes and images are drawn onto the existing bitmap, once they have had globalAlpha and the current transformation matrix applied. It must be set to a value from the following list. In the descriptions below, the source image, A, is the shape or image being rendered, and the destination image, B, is the current state of the bitmap.

source-atop
A atop B. Display the source image wherever both images are opaque. Display the destination image wherever the destination image is opaque but the source image is transparent. Display transparency elsewhere.
source-in
A in B. Display the source image wherever both the source image and destination image are opaque. Display transparency elsewhere.
source-out
A out B. Display the source image wherever the source image is opaque and the destination image is transparent. Display transparency elsewhere.
source-over (default)
A over B. Display the source image wherever the source image is opaque. Display the destination image elsewhere.
destination-atop
B atop A. Same as source-atop but using the destination image instead of the source image and vice versa.
destination-in
B in A. Same as source-in but using the destination image instead of the source image and vice versa.
destination-out
B out A. Same as source-out but using the destination image instead of the source image and vice versa.
destination-over
B over A. Same as source-over but using the destination image instead of the source image and vice versa.
lighter
A plus B. Display the sum of the source image and destination image, with color values approaching 1 as a limit.
copy
A (B is ignored). Display the source image instead of the destination image.
xor
A xor B. Exclusive OR of the source image and destination image.
vendorName-operationName
Vendor-specific extensions to the list of composition operators should use this syntax.

These values are all case-sensitive — they must be used exactly as shown. User agents must not recognize values that are not a case-sensitive match for one of the values given above.

The operators in the above list must be treated as described by the Porter-Duff operator given at the start of their description (e.g. A over B). [PORTERDUFF]

On setting, if the user agent does not recognize the specified value, it must be ignored, leaving the value of globalCompositeOperation unaffected.

When the context is created, the globalCompositeOperation attribute must initially have the value source-over.

4.8.11.1.4 Colors and styles
context . strokeStyle [ = value ]

Returns the current style used for stroking shapes.

Can be set, to change the stroke style.

The style can be either a string containing a CSS color, or a CanvasGradient or CanvasPattern object. Invalid values are ignored.

context . fillStyle [ = value ]

Returns the current style used for filling shapes.

Can be set, to change the fill style.

The style can be either a string containing a CSS color, or a CanvasGradient or CanvasPattern object. Invalid values are ignored.

The strokeStyle attribute represents the color or style to use for the lines around shapes, and the fillStyle attribute represents the color or style to use inside the shapes.

Both attributes can be either strings, CanvasGradients, or CanvasPatterns. On setting, strings must be parsed as CSS <color> values and the color assigned, and CanvasGradient and CanvasPattern objects must be assigned themselves. [CSS3COLOR] If the value is a string but is not a valid color, or is neither a string, a CanvasGradient, nor a CanvasPattern, then it must be ignored, and the attribute must retain its previous value.

On getting, if the value is a color, then the serialization of the color must be returned. Otherwise, if it is not a color but a CanvasGradient or CanvasPattern, then the respective object must be returned. (Such objects are opaque and therefore only useful for assigning to other attributes or for comparison to other gradients or patterns.)

The serialization of a color for a color value is a string, computed as follows: if it has alpha equal to 1.0, then the string is a lowercase six-digit hex value, prefixed with a "#" character (U+0023 NUMBER SIGN), with the first two digits representing the red component, the next two digits representing the green component, and the last two digits representing the blue component, the digits being in the range 0-9 a-f (U+0030 to U+0039 and U+0061 to U+0066). Otherwise, the color value has alpha less than 1.0, and the string is the color value in the CSS rgba() functional-notation format: the literal string rgba (U+0072 U+0067 U+0062 U+0061) followed by a U+0028 LEFT PARENTHESIS, a base-ten integer in the range 0-255 representing the red component (using digits 0-9, U+0030 to U+0039, in the shortest form possible), a literal U+002C COMMA and U+0020 SPACE, an integer for the green component, a comma and a space, an integer for the blue component, another comma and space, a U+0030 DIGIT ZERO, a U+002E FULL STOP (representing the decimal point), one or more digits in the range 0-9 (U+0030 to U+0039) representing the fractional part of the alpha value, and finally a U+0029 RIGHT PARENTHESIS.

When the context is created, the strokeStyle and fillStyle attributes must initially have the string value #000000.


There are two types of gradients, linear gradients and radial gradients, both represented by objects implementing the opaque CanvasGradient interface.

Once a gradient has been created (see below), stops are placed along it to define how the colors are distributed along the gradient. The color of the gradient at each stop is the color specified for that stop. Between each such stop, the colors and the alpha component must be linearly interpolated over the RGBA space without premultiplying the alpha value to find the color to use at that offset. Before the first stop, the color must be the color of the first stop. After the last stop, the color must be the color of the last stop. When there are no stops, the gradient is transparent black.

gradient . addColorStop(offset, color)

Adds a color stop with the given color to the gradient at the given offset. 0.0 is the offset at one end of the gradient, 1.0 is the offset at the other end.

Throws an INDEX_SIZE_ERR exception if the offset it out of range. Throws a SYNTAX_ERR exception if the color cannot be parsed.

gradient = context . createLinearGradient(x0, y0, x1, y1)

Returns a CanvasGradient object that represents a linear gradient that paints along the line given by the coordinates represented by the arguments.

If any of the arguments are not finite numbers, throws a NOT_SUPPORTED_ERR exception.

gradient = context . createRadialGradient(x0, y0, r0, x1, y1, r1)

Returns a CanvasGradient object that represents a radial gradient that paints along the cone given by the circles represented by the arguments.

If any of the arguments are not finite numbers, throws a NOT_SUPPORTED_ERR exception. If either of the radii are negative throws an INDEX_SIZE_ERR exception.

The addColorStop(offset, color) method on the CanvasGradient interface adds a new stop to a gradient. If the offset is less than 0, greater than 1, infinite, or NaN, then an INDEX_SIZE_ERR exception must be raised. If the color cannot be parsed as a CSS color, then a SYNTAX_ERR exception must be raised. Otherwise, the gradient must have a new stop placed, at offset offset relative to the whole gradient, and with the color obtained by parsing color as a CSS <color> value. If multiple stops are added at the same offset on a gradient, they must be placed in the order added, with the first one closest to the start of the gradient, and each subsequent one infinitesimally further along towards the end point (in effect causing all but the first and last stop added at each point to be ignored).

The createLinearGradient(x0, y0, x1, y1) method takes four arguments that represent the start point (x0, y0) and end point (x1, y1) of the gradient. If any of the arguments to createLinearGradient() are infinite or NaN, the method must raise a NOT_SUPPORTED_ERR exception. Otherwise, the method must return a linear CanvasGradient initialized with the specified line.

Linear gradients must be rendered such that all points on a line perpendicular to the line that crosses the start and end points have the color at the point where those two lines cross (with the colors coming from the interpolation and extrapolation described above). The points in the linear gradient must be transformed as described by the current transformation matrix when rendering.

If x0 = x1 and y0 = y1, then the linear gradient must paint nothing.

The createRadialGradient(x0, y0, r0, x1, y1, r1) method takes six arguments, the first three representing the start circle with origin (x0, y0) and radius r0, and the last three representing the end circle with origin (x1, y1) and radius r1. The values are in coordinate space units. If any of the arguments are infinite or NaN, a NOT_SUPPORTED_ERR exception must be raised. If either of r0 or r1 are negative, an INDEX_SIZE_ERR exception must be raised. Otherwise, the method must return a radial CanvasGradient initialized with the two specified circles.

Radial gradients must be rendered by following these steps:

  1. If x0 = x1 and y0 = y1 and r0 = r1, then the radial gradient must paint nothing. Abort these steps.

  2. Let x(ω) = (x1-x0)ω + x0

    Let y(ω) = (y1-y0)ω + y0

    Let r(ω) = (r1-r0)ω + r0

    Let the color at ω be the color at that position on the gradient (with the colors coming from the interpolation and extrapolation described above).

  3. For all values of ω where r(ω) > 0, starting with the value of ω nearest to positive infinity and ending with the value of ω nearest to negative infinity, draw the circumference of the circle with radius r(ω) at position (x(ω), y(ω)), with the color at ω, but only painting on the parts of the canvas that have not yet been painted on by earlier circles in this step for this rendering of the gradient.

This effectively creates a cone, touched by the two circles defined in the creation of the gradient, with the part of the cone before the start circle (0.0) using the color of the first offset, the part of the cone after the end circle (1.0) using the color of the last offset, and areas outside the cone untouched by the gradient (transparent black).

Gradients must be painted only where the relevant stroking or filling effects requires that they be drawn.

The points in the radial gradient must be transformed as described by the current transformation matrix when rendering.


Patterns are represented by objects implementing the opaque CanvasPattern interface.

pattern = context . createPattern(image, repetition)

Returns a CanvasPattern object that uses the given image and repeats in the direction(s) given by the repetition argument.

The allowed values for repeat are repeat (both directions), repeat-x (horizontal only), repeat-y (vertical only), and no-repeat (neither). If the repetition argument is empty or null, the value repeat is used.

If the first argument isn't an img, canvas, or video element, throws a TYPE_MISMATCH_ERR exception. If the image is not fully decoded yet, or has no image data, throws an INVALID_STATE_ERR exception. If the second argument isn't one of the allowed values, throws a SYNTAX_ERR exception.

To create objects of this type, the createPattern(image, repetition) method is used. The first argument gives the image to use as the pattern (either an HTMLImageElement or an HTMLCanvasElement). Modifying this image after calling the createPattern() method must not affect the pattern. The second argument must be a string with one of the following values: repeat, repeat-x, repeat-y, no-repeat. If the empty string or null is specified, repeat must be assumed. If an unrecognized value is given, then the user agent must raise a SYNTAX_ERR exception. User agents must recognize the four values described above exactly (e.g. they must not do case folding). The method must return a CanvasPattern object suitably initialized.

The image argument must be an instance of HTMLImageElement, HTMLCanvasElement, or HTMLVideoElement. If the image is of the wrong type or null, the implementation must raise a TYPE_MISMATCH_ERR exception.

If the image argument is an HTMLImageElement object whose complete attribute is false, then the implementation must raise an INVALID_STATE_ERR exception.

If the image argument is an HTMLVideoElement object whose readyState attribute is either HAVE_NOTHING or HAVE_METADATA, then the implementation must raise an INVALID_STATE_ERR exception.

If the image argument is an HTMLCanvasElement object with either a horizontal dimension or a vertical dimension equal to zero, then the implementation must raise an INVALID_STATE_ERR exception.

Patterns must be painted so that the top left of the first image is anchored at the origin of the coordinate space, and images are then repeated horizontally to the left and right (if the repeat-x string was specified) or vertically up and down (if the repeat-y string was specified) or in all four directions all over the canvas (if the repeat string was specified). The images are not scaled by this process; one CSS pixel of the image must be painted on one coordinate space unit. Of course, patterns must actually be painted only where the stroking or filling effect requires that they be drawn, and are affected by the current transformation matrix.

When the createPattern() method is passed, as its image argument, an animated image, the poster frame of the animation, or the first frame of the animation if there is no poster frame, must be used.

When the image argument is an HTMLVideoElement, then the frame at the current playback position must be used as the source image.

4.8.11.1.5 Line styles
context . lineWidth [ = value ]

Returns the current line width.

Can be set, to change the line width. Values that are not finite values greater than zero are ignored.

context . lineCap [ = value ]

Returns the current line cap style.

Can be set, to change the line cap style.

The possible line cap styles are butt, round, and square. Other values are ignored.

context . lineJoin [ = value ]

Returns the current line join style.

Can be set, to change the line join style.

The possible line join styles are bevel, round, and miter. Other values are ignored.

context . miterLimit [ = value ]

Returns the current miter limit ratio.

Can be set, to change the miter limit ratio. Values that are not finite values greater than zero are ignored.

The lineWidth attribute gives the width of lines, in coordinate space units. On setting, zero, negative, infinite, and NaN values must be ignored, leaving the value unchanged.

When the context is created, the lineWidth attribute must initially have the value 1.0.

The lineCap attribute defines the type of endings that UAs will place on the end of lines. The three valid values are butt, round, and square. The butt value means that the end of each line has a flat edge perpendicular to the direction of the line (and that no additional line cap is added). The round value means that a semi-circle with the diameter equal to the width of the line must then be added on to the end of the line. The square value means that a rectangle with the length of the line width and the width of half the line width, placed flat against the edge perpendicular to the direction of the line, must be added at the end of each line. On setting, any other value than the literal strings butt, round, and square must be ignored, leaving the value unchanged.

When the context is created, the lineCap attribute must initially have the value butt.

The lineJoin attribute defines the type of corners that UAs will place where two lines meet. The three valid values are bevel, round, and miter.

On setting, any other value than the literal strings bevel, round, and miter must be ignored, leaving the value unchanged.

When the context is created, the lineJoin attribute must initially have the value miter.

A join exists at any point in a subpath shared by two consecutive lines. When a subpath is closed, then a join also exists at its first point (equivalent to its last point) connecting the first and last lines in the subpath.

In addition to the point where the join occurs, two additional points are relevant to each join, one for each line: the two corners found half the line width away from the join point, one perpendicular to each line, each on the side furthest from the other line.

A filled triangle connecting these two opposite corners with a straight line, with the third point of the triangle being the join point, must be rendered at all joins. The lineJoin attribute controls whether anything else is rendered. The three aforementioned values have the following meanings:

The bevel value means that this is all that is rendered at joins.

The round value means that a filled arc connecting the two aforementioned corners of the join, abutting (and not overlapping) the aforementioned triangle, with the diameter equal to the line width and the origin at the point of the join, must be rendered at joins.

The miter value means that a second filled triangle must (if it can given the miter length) be rendered at the join, with one line being the line between the two aforementioned corners, abutting the first triangle, and the other two being continuations of the outside edges of the two joining lines, as long as required to intersect without going over the miter length.

The miter length is the distance from the point where the lines touch on the inside of the join to the intersection of the line edges on the outside of the join. The miter limit ratio is the maximum allowed ratio of the miter length to half the line width. If the miter length would cause the miter limit ratio to be exceeded, this second triangle must not be rendered.

The miter limit ratio can be explicitly set using the miterLimit attribute. On setting, zero, negative, infinite, and NaN values must be ignored, leaving the value unchanged.

When the context is created, the miterLimit attribute must initially have the value 10.0.

4.8.11.1.6 Shadows

All drawing operations are affected by the four global shadow attributes.

context . shadowColor [ = value ]

Returns the current shadow color.

Can be set, to change the shadow color. Values that cannot be parsed as CSS colors are ignored.

context . shadowOffsetX [ = value ]
context . shadowOffsetY [ = value ]

Returns the current shadow offset.

Can be set, to change the shadow offset. Values that are not finite numbers are ignored.

context . shadowBlur [ = value ]

Returns the current level of blur applied to shadows.

Can be set, to change the blur level. Values that are not finite numbers greater than or equal to zero are ignored.

The shadowColor attribute sets the color of the shadow.

When the context is created, the shadowColor attribute initially must be fully-transparent black.

On getting, the serialization of the color must be returned.

On setting, the new value must be parsed as a CSS <color> value and the color assigned. If the value is not a valid color, then it must be ignored, and the attribute must retain its previous value. [CSS3COLOR]

The shadowOffsetX and shadowOffsetY attributes specify the distance that the shadow will be offset in the positive horizontal and positive vertical distance respectively. Their values are in coordinate space units. They are not affected by the current transformation matrix.

When the context is created, the shadow offset attributes must initially have the value 0.

On getting, they must return their current value. On setting, the attribute being set must be set to the new value, except if the value is infinite or NaN, in which case the new value must be ignored.

The shadowBlur attribute specifies the size of the blurring effect. (The units do not map to coordinate space units, and are not affected by the current transformation matrix.)

When the context is created, the shadowBlur attribute must initially have the value 0.

On getting, the attribute must return its current value. On setting the attribute must be set to the new value, except if the value is negative, infinite or NaN, in which case the new value must be ignored.

Shadows are only drawn if either the opacity component of the alpha component of the color of shadowColor is non-zero, or the shadowBlur is non-zero, or the shadowOffsetX is non-zero, or the shadowOffsetY is non-zero.

When shadows are drawn, they must be rendered as follows:

  1. Let A be the source image for which a shadow is being created.

  2. Let B be an infinite transparent black bitmap, with a coordinate space and an origin identical to A.

  3. Copy the alpha channel of A to B, offset by shadowOffsetX in the positive x direction, and shadowOffsetY in the positive y direction.

  4. If shadowBlur is greater than 0:

    1. If shadowBlur is less than 8, let σ be half the value of shadowBlur; otherwise, let σ be the square root of multiplying the value of shadowBlur by 2.

    2. Perform a 2D Gaussian Blur on B, using σ as the standard deviation.

    User agents may limit values of σ to an implementation-specific maximum value to avoid exceeding hardware limitations during the Gaussian blur operation.

  5. Set the red, green, and blue components of every pixel in B to the red, green, and blue components (respectively) of the color of shadowColor.

  6. Multiply the alpha component of every pixel in B by the alpha component of the color of shadowColor.

  7. The shadow is in the bitmap B, and is rendered as part of the drawing model described below.

4.8.11.1.7 Simple shapes (rectangles)

There are three methods that immediately draw rectangles to the bitmap. They each take four arguments; the first two give the x and y coordinates of the top left of the rectangle, and the second two give the width w and height h of the rectangle, respectively.

The current transformation matrix must be applied to the following four coordinates, which form the path that must then be closed to get the specified rectangle: (x, y), (x+w, y), (x+w, y+h), (x, y+h).

Shapes are painted without affecting the current path, and are subject to the clipping region, and, with the exception of clearRect(), also shadow effects, global alpha, and global composition operators.

context . clearRect(x, y, w, h)

Clears all pixels on the canvas in the given rectangle to transparent black.

context . fillRect(x, y, w, h)

Paints the given rectangle onto the canvas, using the current fill style.

context . strokeRect(x, y, w, h)

Paints the box that outlines the given rectangle onto the canvas, using the current stroke style.

The clearRect(x, y, w, h) method must clear the pixels in the specified rectangle that also intersect the current clipping region to a fully transparent black, erasing any previous image. If either height or width are zero, this method has no effect.

The fillRect(x, y, w, h) method must paint the specified rectangular area using the fillStyle. If either height or width are zero, this method has no effect.

The strokeRect(x, y, w, h) method must stroke the specified rectangle's path using the strokeStyle, lineWidth, lineJoin, and (if appropriate) miterLimit attributes. If both height and width are zero, this method has no effect, since there is no path to stroke (it's a point). If only one of the two is zero, then the method will draw a line instead (the path for the outline is just a straight line along the non-zero dimension).

4.8.11.1.8 Complex shapes (paths)

The context always has a current path. There is only one current path, it is not part of the drawing state.

A path has a list of zero or more subpaths. Each subpath consists of a list of one or more points, connected by straight or curved lines, and a flag indicating whether the subpath is closed or not. A closed subpath is one where the last point of the subpath is connected to the first point of the subpath by a straight line. Subpaths with fewer than two points are ignored when painting the path.

context . beginPath()

Resets the current path.

context . moveTo(x, y)

Creates a new subpath with the given point.

context . closePath()

Marks the current subpath as closed, and starts a new subpath with a point the same as the start and end of the newly closed subpath.

context . lineTo(x, y)

Adds the given point to the current subpath, connected to the previous one by a straight line.

context . quadraticCurveTo(cpx, cpy, x, y)

Adds the given point to the current path, connected to the previous one by a quadratic Bézier curve with the given control point.

context . bezierCurveTo(cpx, cpy, x, y)

Adds the given point to the current path, connected to the previous one by a cubic Bézier curve with the given control points.

context . arcTo(x1, y1, x2, y2, radius)

Adds a point to the current path, connected to the previous one by a straight line, then adds a second point to the current path, connected to the previous one by an arc whose properties are described by the arguments.

Throws an INDEX_SIZE_ERR exception if the given radius is negative.

context . arc(x, y, radius, startAngle, endAngle, anticlockwise)

Adds points to the subpath such that the arc described by the circumference of the circle described by the arguments, starting at the given start angle and ending at the given end angle, going in the given direction, is added to the path, connected to the previous point by a straight line.

Throws an INDEX_SIZE_ERR exception if the given radius is negative.

context . rect(x, y, w, h)

Adds a new closed subpath to the path, representing the given rectangle.

context . fill()

Fills the subpaths with the current fill style.

context . stroke()

Strokes the subpaths with the current stroke style.

context . clip()

Further constrains the clipping region to the given path.

context . isPointInPath(x, y)

Returns true if the given point is in the current path.

Initially, the context's path must have zero subpaths.

The points and lines added to the path by these methods must be transformed according to the current transformation matrix as they are added.

The beginPath() method must empty the list of subpaths so that the context once again has zero subpaths.

The moveTo(x, y) method must create a new subpath with the specified point as its first (and only) point.

The closePath() method must do nothing if the context has no subpaths. Otherwise, it must mark the last subpath as closed, create a new subpath whose first point is the same as the previous subpath's first point, and finally add this new subpath to the path. (If the last subpath had more than one point in its list of points, then this is equivalent to adding a straight line connecting the last point back to the first point, thus "closing" the shape, and then repeating the last moveTo() call.)

New points and the lines connecting them are added to subpaths using the methods described below. In all cases, the methods only modify the last subpath in the context's paths.

The lineTo(x, y) method must do nothing if the context has no subpaths. Otherwise, it must connect the last point in the subpath to the given point (x, y) using a straight line, and must then add the given point (x, y) to the subpath.

The quadraticCurveTo(cpx, cpy, x, y) method must do nothing if the context has no subpaths. Otherwise it must connect the last point in the subpath to the given point (x, y) using a quadratic Bézier curve with control point (cpx, cpy), and must then add the given point (x, y) to the subpath. [BEZIER]

The bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y) method must do nothing if the context has no subpaths. Otherwise, it must connect the last point in the subpath to the given point (x, y) using a cubic Bézier curve with control points (cp1x, cp1y) and (cp2x, cp2y). Then, it must add the point (x, y) to the subpath. [BEZIER]

The arcTo(x1, y1, x2, y2, radius) method must do nothing if the context has no subpaths. If the context does have a subpath, then the behavior depends on the arguments and the last point in the subpath.

Negative values for radius must cause the implementation to raise an INDEX_SIZE_ERR exception.

Let the point (x0, y0) be the last point in the subpath.

If the point (x0, y0) is equal to the point (x1, y1), or if the point (x1, y1) is equal to the point (x2, y2), or if the radius radius is zero, then the method must add the point (x1, y1) to the subpath, and connect that point to the previous point (x0, y0) by a straight line.

Otherwise, if the points (x0, y0), (x1, y1), and (x2, y2) all lie on a single straight line, then the method must add the point (x1, y1) to the subpath, and connect that point to the previous point (x0, y0) by a straight line.

Otherwise, let The Arc be the shortest arc given by circumference of the circle that has radius radius, and that has one point tangent to the half-infinite line that crosses the point (x0, y0) and ends at the point (x1, y1), and that has a different point tangent to the half-infinite line that ends at the point (x1, y1) and crosses the point (x2, y2). The points at which this circle touches these two lines are called the start and end tangent points respectively.

The method must connect the point (x0, y0) to the start tangent point by a straight line, adding the start tangent point to the subpath, and then must connect the start tangent point to the end tangent point by The Arc, adding the end tangent point to the subpath.

The arc(x, y, radius, startAngle, endAngle, anticlockwise) method draws an arc. If the context has any subpaths, then the method must add a straight line from the last point in the subpath to the start point of the arc. In any case, it must draw the arc between the start point of the arc and the end point of the arc, and add the start and end points of the arc to the subpath. The arc and its start and end points are defined as follows:

Consider a circle that has its origin at (x, y) and that has radius radius. The points at startAngle and endAngle along this circle's circumference, measured in radians clockwise from the positive x-axis, are the start and end points respectively.

If the anticlockwise argument is false and endAngle-startAngle is equal to or greater than , or, if the anticlockwise argument is true and startAngle-endAngle is equal to or greater than , then the arc is the whole circumference of this circle.

Otherwise, the arc is the path along the circumference of this circle from the start point to the end point, going anti-clockwise if the anticlockwise argument is true, and clockwise otherwise. Since the points are on the circle, as opposed to being simply angles from zero, the arc can never cover an angle greater than radians. If the two points are the same, or if the radius is zero, then the arc is defined as being of zero length in both directions.

Negative values for radius must cause the implementation to raise an INDEX_SIZE_ERR exception.

The rect(x, y, w, h) method must create a new subpath containing just the four points (x, y), (x+w, y), (x+w, y+h), (x, y+h), with those four points connected by straight lines, and must then mark the subpath as closed. It must then create a new subpath with the point (x, y) as the only point in the subpath.

The fill() method must fill all the subpaths of the current path, using fillStyle, and using the non-zero winding number rule. Open subpaths must be implicitly closed when being filled (without affecting the actual subpaths).

Thus, if two overlapping but otherwise independent subpaths have opposite windings, they cancel out and result in no fill. If they have the same winding, that area just gets painted once.

The stroke() method must calculate the strokes of all the subpaths of the current path, using the lineWidth, lineCap, lineJoin, and (if appropriate) miterLimit attributes, and then fill the combined stroke area using the strokeStyle attribute.

Since the subpaths are all stroked as one, overlapping parts of the paths in one stroke operation are treated as if their union was what was painted.

Paths, when filled or stroked, must be painted without affecting the current path, and must be subject to shadow effects, global alpha, the clipping region, and global composition operators. (Transformations affect the path when the path is created, not when it is painted, though the stroke style is still affected by the transformation during painting.)

Zero-length line segments must be pruned before stroking a path. Empty subpaths must be ignored.

The clip() method must create a new clipping region by calculating the intersection of the current clipping region and the area described by the current path, using the non-zero winding number rule. Open subpaths must be implicitly closed when computing the clipping region, without affecting the actual subpaths. The new clipping region replaces the current clipping region.

When the context is initialized, the clipping region must be set to the rectangle with the top left corner at (0,0) and the width and height of the coordinate space.

The isPointInPath(x, y) method must return true if the point given by the x and y coordinates passed to the method, when treated as coordinates in the canvas coordinate space unaffected by the current transformation, is inside the current path as determined by the non-zero winding number rule; and must return false otherwise. Points on the path itself are considered to be inside the path. If either of the arguments is infinite or NaN, then the method must return false.

4.8.11.1.9 Text
context . font [ = value ]

Returns the current font settings.

Can be set, to change the font. The syntax is the same as for the CSS 'font' property; values that cannot be parsed as CSS font values are ignored.

Relative keywords and lengths are computed relative to the default font, 10px sans-serif.

context . textAlign [ = value ]

Returns the current text alignment settings.

Can be set, to change the alignment. The possible values are start, end, left, right, and center. The default is start. Other values are ignored.

context . textBaseline [ = value ]

Returns the current baseline alignment settings.

Can be set, to change the baseline alignment. The possible values and their meanings are given below. The default is alphabetic. Other values are ignored.

context . fillText(text, x, y [, maxWidth ] )
context . strokeText(text, x, y [, maxWidth ] )

Fills or strokes (respectively) the given text at the given position. If a maximum width is provided, the text will be scaled to fit that width if necessary.

metrics = context . measureText(text)

Returns a TextMetrics object with the metrics of the given text in the current font.

metrics . width

Returns the advance width of the text that was passed to the measureText() method.

The font DOM attribute, on setting, must be parsed the same way as the 'font' property of CSS (but without supporting property-independent stylesheet syntax like 'inherit'), and the resulting font must be assigned to the context, with the 'line-height' component forced to 'normal'. If the new value is syntactically incorrect, then it must be ignored, without assigning a new font value. [CSS]

Font names must be interpreted in the context of the canvas element's stylesheets; any fonts embedded using @font-face must therefore be available. [CSSWEBFONTS]

Only vector fonts should be used by the user agent; if a user agent were to use bitmap fonts then transformations would likely make the font look very ugly.

On getting, the font attribute must return the serialized form of the current font of the context. [CSSOM]

When the context is created, the font of the context must be set to 10px sans-serif. When the 'font-size' component is set to lengths using percentages, 'em' or 'ex' units, or the 'larger' or 'smaller' keywords, these must be interpreted relative to the computed value of the 'font-size' property of the corresponding canvas element at the time that the attribute is set. When the 'font-weight' component is set to the relative values 'bolder' and 'lighter', these must be interpreted relative to the computed value of the 'font-weight' property of the corresponding canvas element at the time that the attribute is set. If the computed values are undefined for a particular case (e.g. because the canvas element is not in a document), then the relative keywords must be interpreted relative to the normal-weight 10px sans-serif default.

The textAlign DOM attribute, on getting, must return the current value. On setting, if the value is one of start, end, left, right, or center, then the value must be changed to the new value. Otherwise, the new value must be ignored. When the context is created, the textAlign attribute must initially have the value start.

The textBaseline DOM attribute, on getting, must return the current value. On setting, if the value is one of top, hanging, middle, alphabetic, ideographic, or bottom, then the value must be changed to the new value. Otherwise, the new value must be ignored. When the context is created, the textBaseline attribute must initially have the value alphabetic.

The textBaseline attribute's allowed keywords correspond to alignment points in the font:

The top of the em square is
  roughly at the top of the glyphs in a font, the hanging baseline is
  where some glyphs like आ are anchored, the middle is half-way
  between the top of the em square and the bottom of the em square,
  the alphabetic baseline is where characters like Á, ÿ,
  f, and Ω are anchored, the ideographic baseline is
  where glyphs like 私 and 達 are anchored, and the bottom
  of the em square is roughly at the bottom of the glyphs in a
  font. The top and bottom of the bounding box can be far from these
  baselines, due to glyphs extending far outside the em square.

The keywords map to these alignment points as follows:

top
The top of the em square
hanging
The hanging baseline
middle
The middle of the em square
alphabetic
The alphabetic baseline
ideographic
The ideographic baseline
bottom
The bottom of the em square

The fillText() and strokeText() methods take three or four arguments, text, x, y, and optionally maxWidth, and render the given text at the given (x, y) coordinates ensuring that the text isn't wider than maxWidth if specified, using the current font, textAlign, and textBaseline values. Specifically, when the methods are called, the user agent must run the following steps:

  1. Let font be the current font of the context, as given by the font attribute.

  2. Replace all the space characters in text with U+0020 SPACE characters.

  3. Form a hypothetical infinitely wide CSS line box containing a single inline box containing the text text, with all the properties at their initial values except the 'font' property of the inline box set to font and the 'direction' property of the inline box set to the directionality of the canvas element. [CSS]

  4. If the maxWidth argument was specified and the hypothetical width of the inline box in the hypothetical line box is greater than maxWidth CSS pixels, then change font to have a more condensed font (if one is available or if a reasonably readable one can be synthesized by applying a horizontal scale factor to the font) or a smaller font, and return to the previous step.

  5. Let the anchor point be a point on the inline box, determined by the textAlign and textBaseline values, as follows:

    Horizontal position:

    If textAlign is left
    If textAlign is start and the directionality of the canvas element is 'ltr'
    If textAlign is end and the directionality of the canvas element is 'rtl'
    Let the anchor point's horizontal position be the left edge of the inline box.
    If textAlign is right
    If textAlign is end and the directionality of the canvas element is 'ltr'
    If textAlign is start and the directionality of the canvas element is 'rtl'
    Let the anchor point's horizontal position be the right edge of the inline box.
    If textAlign is center
    Let the anchor point's horizontal position be half way between the left and right edges of the inline box.

    Vertical position:

    If textBaseline is top
    Let the anchor point's vertical position be the top of the em box of the first available font of the inline box.
    If textBaseline is hanging
    Let the anchor point's vertical position be the hanging baseline of the first available font of the inline box.
    If textBaseline is middle
    Let the anchor point's vertical position be half way between the bottom and the top of the em box of the first available font of the inline box.
    If textBaseline is alphabetic
    Let the anchor point's vertical position be the alphabetic baseline of the first available font of the inline box.
    If textBaseline is ideographic
    Let the anchor point's vertical position be the ideographic baseline of the first available font of the inline box.
    If textBaseline is bottom
    Let the anchor point's vertical position be the bottom of the em box of the first available font of the inline box.
  6. Paint the hypothetical inline box as the shape given by the text's glyphs, as transformed by the current transformation matrix, and anchored and sized so that before applying the current transformation matrix, the anchor point is at (x, y) and each CSS pixel is mapped to one coordinate space unit.

    For fillText() fillStyle must be applied to the glyphs and strokeStyle must be ignored. For strokeText() the reverse holds and strokeStyle must be applied to the glyph outlines and fillStyle must be ignored.

    Text is painted without affecting the current path, and is subject to shadow effects, global alpha, the clipping region, and global composition operators.

The measureText() method takes one argument, text. When the method is invoked, the user agent must replace all the space characters in text with U+0020 SPACE characters, and then must form a hypothetical infinitely wide CSS line box containing a single inline box containing the text text, with all the properties at their initial values except the 'font' property of the inline element set to the current font of the context, as given by the font attribute, and must then return a new TextMetrics object with its width attribute set to the width of that inline box, in CSS pixels. [CSS]

The TextMetrics interface is used for the objects returned from measureText(). It has one attribute, width, which is set by the measureText() method.

Glyphs rendered using fillText() and strokeText() can spill out of the box given by the font size (the em square size) and the width returned by measureText() (the text width). This version of the specification does not provide a way to obtain the bounding box dimensions of the text. If the text is to be rendered and removed, care needs to be taken to replace the entire area of the canvas that the clipping region covers, not just the box given by the em square height and measured text width.

A future version of the 2D context API may provide a way to render fragments of documents, rendered using CSS, straight to the canvas. This would be provided in preference to a dedicated way of doing multiline layout.

4.8.11.1.10 Images

To draw images onto the canvas, the drawImage method can be used.

This method can be invoked with three different sets of arguments:

Each of those three can take either an HTMLImageElement, an HTMLCanvasElement, or an HTMLVideoElement for the image argument.

context . drawImage(image, dx, dy)
context . drawImage(image, dx, dy, dw, dh)
context . drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh)

Draws the given image onto the canvas. The arguments are interpreted as per the diagram below.

If the first argument isn't an img, canvas, or video element, throws a TYPE_MISMATCH_ERR exception. If the image is not fully decoded yet, or has no image data, throws an INVALID_STATE_ERR exception. If the second argument isn't one of the allowed values, throws a SYNTAX_ERR exception.

If not specified, the dw and dh arguments must default to the values of sw and sh, interpreted such that one CSS pixel in the image is treated as one unit in the canvas coordinate space. If the sx, sy, sw, and sh arguments are omitted, they must default to 0, 0, the image's intrinsic width in image pixels, and the image's intrinsic height in image pixels, respectively.

The image argument must be an instance of HTMLImageElement, HTMLCanvasElement, or HTMLVideoElement. If the image is of the wrong type or null, the implementation must raise a TYPE_MISMATCH_ERR exception.

If the image argument is an HTMLImageElement object whose complete attribute is false, then the implementation must raise an INVALID_STATE_ERR exception.

If the image argument is an HTMLVideoElement object whose readyState attribute is either HAVE_NOTHING or HAVE_METADATA, then the implementation must raise an INVALID_STATE_ERR exception.

If the image argument is an HTMLCanvasElement object with either a horizontal dimension or a vertical dimension equal to zero, then the implementation must raise an INVALID_STATE_ERR exception.

The source rectangle is the rectangle whose corners are the four points (sx, sy), (sx+sw, sy), (sx+sw, sy+sh), (sx, sy+sh).

If the source rectangle is not entirely within the source image, or if one of the sw or sh arguments is zero, the implementation must raise an INDEX_SIZE_ERR exception.

The destination rectangle is the rectangle whose corners are the four points (dx, dy), (dx+dw, dy), (dx+dw, dy+dh), (dx, dy+dh).

When drawImage() is invoked, the region of the image specified by the source rectangle must be painted on the region of the canvas specified by the destination rectangle, after applying the current transformation matrix to the points of the destination rectangle.

When a canvas is drawn onto itself, the drawing model requires the source to be copied before the image is drawn back onto the canvas, so it is possible to copy parts of a canvas onto overlapping parts of itself.

When the drawImage() method is passed, as its image argument, an HTMLImageElement representing an animated image, the poster frame of the animation, or the first frame of the animation if there is no poster frame, must be used.

When the image argument is an HTMLVideoElement, then the frame at the current playback position must be used as the source image.

Images are painted without affecting the current path, and are subject to shadow effects, global alpha, the clipping region, and global composition operators.

4.8.11.1.11 Pixel manipulation
imagedata = context . createImageData(sw, sh)

Returns an ImageData object with the given dimensions in CSS pixels (which might map to a different number of actual device pixels exposed by the object itself). All the pixels in the returned object are transparent black.

imagedata = context . createImageData(imagedata)

Returns an ImageData object with the same dimensions as the argument. All the pixels in the returned object are transparent black.

Throws a NOT_SUPPORTED_ERR exception if the argument is null.

imagedata = context . getImageData(sx, sy, sw, sh)

Returns an ImageData object containing the image data for the given rectangle of the canvas.

Throws a NOT_SUPPORTED_ERR exception if any of the arguments are not finite. Throws an INDEX_SIZE_ERR exception if the either of the width or height arguments are zero.

imagedata . width
imagedata . height

Returns the actual dimensions of the data in the ImageData object, in device pixels.

imagedata . data

Returns the one-dimensional array containing the data.

context . putImageData(imagedata, dx, dy [, dirtyX, dirtyY, dirtyWidth, dirtyHeight ])

Paints the data from the given ImageData object onto the canvas. If a dirty rectangle is provided, only the pixels from that rectangle are painted.

If the first argument isn't an ImageData object, throws a TYPE_MISMATCH_ERR exception. Throws a NOT_SUPPORTED_ERR exception if any of the other arguments are not finite.

The createImageData() method is used to instantiate new blank ImageData objects. When the method is invoked with two arguments sw and sh, it must return an ImageData object representing a rectangle with a width in CSS pixels equal to the absolute magnitude of sw and a height in CSS pixels equal to the absolute magnitude of sh. When invoked with a single imagedata argument, it must return an ImageData object representing a rectangle with the same dimensions as the ImageData object passed as the argument. The ImageData object return must be filled with transparent black.

The getImageData(sx, sy, sw, sh) method must return an ImageData object representing the underlying pixel data for the area of the canvas denoted by the rectangle whose corners are the four points (sx, sy), (sx+sw, sy), (sx+sw, sy+sh), (sx, sy+sh), in canvas coordinate space units. Pixels outside the canvas must be returned as transparent black. Pixels must be returned as non-premultiplied alpha values.

If any of the arguments to createImageData() or getImageData() are infinite or NaN, or if the createImageData() method is invoked with only one argument but that argument is null, the method must instead raise a NOT_SUPPORTED_ERR exception. If either the sw or sh arguments are zero, the method must instead raise an INDEX_SIZE_ERR exception.

ImageData objects must be initialized so that their width attribute is set to w, the number of physical device pixels per row in the image data, their height attribute is set to h, the number of rows in the image data, and their data attribute is initialized to a CanvasPixelArray object holding the image data. At least one pixel's worth of image data must be returned.

The CanvasPixelArray object provides ordered, indexed access to the color components of each pixel of the image data. The data must be represented in left-to-right order, row by row top to bottom, starting with the top left, with each pixel's red, green, blue, and alpha components being given in that order for each pixel. Each component of each device pixel represented in this array must be in the range 0..255, representing the 8 bit value for that component. The components must be assigned consecutive indices starting with 0 for the top left pixel's red component.

The CanvasPixelArray object thus represents h×w×4 integers. The length attribute of a CanvasPixelArray object must return this number.

The object's indices of the supported indexed properties are the numbers in the range 0 .. h×w×4-1.

When a CanvasPixelArray object is indexed to retrieve an indexed property index, the value returned must be the value of the indexth component in the array.

When a CanvasPixelArray object is indexed to modify an indexed property index with value value, the value of the indexth component in the array must be set to value. JS undefined values must be converted to zero. Other values must first be converted to numbers using JavaScript's ToNumber algorithm, and if the result is a NaN value, then the value must be converted to zero. If the result is less than 0, it must be clamped to zero. If the result is more than 255, it must be clamped to 255. If the number is not an integer, it should be rounded to the nearest integer using the IEEE 754r convertToIntegerTiesToEven rounding mode. [ECMA262] [IEEE754R]

The width and height (w and h) might be different from the sw and sh arguments to the above methods, e.g. if the canvas is backed by a high-resolution bitmap, or if the sw and sh arguments are negative.

The putImageData(imagedata, dx, dy, dirtyX, dirtyY, dirtyWidth, dirtyHeight) method writes data from ImageData structures back to the canvas.

If any of the arguments to the method are infinite or NaN, the method must raise a NOT_SUPPORTED_ERR exception.

If the first argument to the method is null or not an ImageData object then the putImageData() method must raise a TYPE_MISMATCH_ERR exception.

When the last four arguments are omitted, they must be assumed to have the values 0, 0, the width member of the imagedata structure, and the height member of the imagedata structure, respectively.

When invoked with arguments that do not, per the last few paragraphs, cause an exception to be raised, the putImageData() method must act as follows:

  1. Let dxdevice be the x-coordinate of the device pixel in the underlying pixel data of the canvas corresponding to the dx coordinate in the canvas coordinate space.

    Let dydevice be the y-coordinate of the device pixel in the underlying pixel data of the canvas corresponding to the dy coordinate in the canvas coordinate space.

  2. If dirtyWidth is negative, let dirtyX be dirtyX+dirtyWidth, and let dirtyWidth be equal to the absolute magnitude of dirtyWidth.

    If dirtyHeight is negative, let dirtyY be dirtyY+dirtyHeight, and let dirtyHeight be equal to the absolute magnitude of dirtyHeight.

  3. If dirtyX is negative, let dirtyWidth be dirtyWidth+dirtyX, and let dirtyX be zero.

    If dirtyY is negative, let dirtyHeight be dirtyHeight+dirtyY, and let dirtyY be zero.

  4. If dirtyX+dirtyWidth is greater than the width attribute of the imagedata argument, let dirtyWidth be the value of that width attribute, minus the value of dirtyX.

    If dirtyY+dirtyHeight is greater than the height attribute of the imagedata argument, let dirtyHeight be the value of that height attribute, minus the value of dirtyY.

  5. If, after those changes, either dirtyWidth or dirtyHeight is negative or zero, stop these steps without affecting the canvas.

  6. Otherwise, for all integer values of x and y where dirtyX ≤ x < dirtyX+dirtyWidth and dirtyY ≤ y < dirtyY+dirtyHeight, copy the four channels of the pixel with coordinate (x, y) in the imagedata data structure to the pixel with coordinate (dxdevice+x, dydevice+y) in the underlying pixel data of the canvas.

The handling of pixel rounding when the specified coordinates do not exactly map to the device coordinate space is not defined by this specification, except that the following must result in no visible changes to the rendering:

context.putImageData(context.getImageData(x, y, w, h), x, y);

...for any value of x, y, w, and h, and the following two calls:

context.createImageData(w, h);
context.getImageData(0, 0, w, h);

...must return ImageData objects with the same dimensions, for any value of w and h. In other words, while user agents may round the arguments of these methods so that they map to device pixel boundaries, any rounding performed must be performed consistently for all of the createImageData(), getImageData() and putImageData() operations.

The current path, transformation matrix, shadow attributes, global alpha, the clipping region, and global composition operator must not affect the getImageData() and putImageData() methods.

The data returned by getImageData() is at the resolution of the canvas backing store, which is likely to not be one device pixel to each CSS pixel if the display used is a high resolution display.

In the following example, the script generates an ImageData object so that it can draw onto it.

// canvas is a reference to a <canvas> element
var context = canvas.getContext('2d');

// create a blank slate
var data = context.createImageData(canvas.width, canvas.height);

// create some plasma
FillPlasma(data, 'green'); // green plasma

// add a cloud to the plasma
AddCloud(data, data.width/2, data.height/2); // put a cloud in the middle

// paint the plasma+cloud on the canvas
context.putImageData(data, 0, 0);

// support methods
function FillPlasma(data, color) { ... }
function AddCloud(data, x, y) { ... }

Here is an example of using getImageData() and putImageData() to implement an edge detection filter.

<!DOCTYPE HTML>
<html>
 <head>
  <title>Edge detection demo</title>
  <script>
   var image = new Image();
   function init() {
     image.onload = demo;
     image.src = "image.jpeg";
   }
   function demo() {
     var canvas = document.getElementsByTagName('canvas')[0];
     var context = canvas.getContext('2d');

     // draw the image onto the canvas
     context.drawImage(image, 0, 0);

     // get the image data to manipulate
     var input = context.getImageData(0, 0, canvas.width, canvas.height);

     // get an empty slate to put the data into
     var output = context.createImageData(canvas.width, canvas.height);

     // alias some variables for convenience
     // notice that we are using input.width and input.height here
     // as they might not be the same as canvas.width and canvas.height
     // (in particular, they might be different on high-res displays)
     var w = input.width, h = input.height;
     var inputData = input.data;
     var outputData = output.data;

     // edge detection
     for (var y = 1; y < h-1; y += 1) {
       for (var x = 1; x < w-1; x += 1) {
         for (var c = 0; c < 3; c += 1) {
           var i = (y*w + x)*4 + c;
           outputData[i] = 127 + -inputData[i - w*4 - 4] -   inputData[i - w*4] - inputData[i - w*4 + 4] +
                                 -inputData[i - 4]       + 8*inputData[i]       - inputData[i + 4] +
                                 -inputData[i + w*4 - 4] -   inputData[i + w*4] - inputData[i + w*4 + 4];
         }
         outputData[(y*w + x)*4 + 3] = 255; // alpha
       }
     }

     // put the image data back after manipulation
     context.putImageData(output, 0, 0);
   }
  </script>
 </head>
 <body onload="init()">
  <canvas></canvas>
 </body>
</html>
4.8.11.1.12 Drawing model

When a shape or image is painted, user agents must follow these steps, in the order given (or act as if they do):

  1. Render the shape or image, creating image A, as described in the previous sections. For shapes, the current fill, stroke, and line styles must be honored, and the stroke must itself also be subjected to the current transformation matrix.

  2. When shadows are drawn, render the shadow from image A, using the current shadow styles, creating image B.

  3. When shadows are drawn, multiply the alpha component of every pixel in B by globalAlpha.

  4. When shadows are drawn, composite B within the clipping region over the current canvas bitmap using the current composition operator.

  5. Multiply the alpha component of every pixel in A by globalAlpha.

  6. Composite A within the clipping region over the current canvas bitmap using the current composition operator.

4.8.11.2 Color spaces and color correction

The canvas APIs must perform color correction at only two points: when rendering images with their own gamma correction and color space information onto the canvas, to convert the image to the color space used by the canvas (e.g. using the drawImage() method with an HTMLImageElement object), and when rendering the actual canvas bitmap to the output device.

Thus, in the 2D context, colors used to draw shapes onto the canvas will exactly match colors obtained through the getImageData() method.

The toDataURL() method must not include color space information in the resource returned. Where the output format allows it, the color of pixels in resources created by toDataURL() must match those returned by the getImageData() method.

In user agents that support CSS, the color space used by a canvas element must match the color space used for processing any colors for that element in CSS.

The gamma correction and color space information of images must be handled in such a way that an image rendered directly using an img element would use the same colors as one painted on a canvas element that is then itself rendered. Furthermore, the rendering of images that have no color correction information (such as those returned by the toDataURL() method) must be rendered with no color correction.

Thus, in the 2D context, calling the drawImage() method to render the output of the toDataURL() method to the canvas, given the appropriate dimensions, has no visible effect.

4.8.11.3 Security with canvas elements

Information leakage can occur if scripts from one origin can access information (e.g. read pixels) from images from another origin (one that isn't the same).

To mitigate this, canvas elements are defined to have a flag indicating whether they are origin-clean. All canvas elements must start with their origin-clean set to true. The flag must be set to false if any of the following actions occur:

Whenever the toDataURL() method of a canvas element whose origin-clean flag is set to false is called, the method must raise a SECURITY_ERR exception.

Whenever the getImageData() method of the 2D context of a canvas element whose origin-clean flag is set to false is called with otherwise correct arguments, the method must raise a SECURITY_ERR exception.

Even resetting the canvas state by changing its width or height attributes doesn't reset the origin-clean flag.

4.8.12 The map element

Categories
Flow content.
When the element only contains phrasing content: phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Transparent.
Content attributes:
Global attributes
name
DOM interface:
interface HTMLMapElement : HTMLElement {
           attribute DOMString name;
  readonly attribute HTMLCollection areas;
  readonly attribute HTMLCollection images;
};

The map element, in conjunction with any area element descendants, defines an image map. The element represents its children.

The name attribute gives the map a name so that it can be referenced. The attribute must be present and must have a non-empty value with no space characters. If the id attribute is also specified, both attributes must have the same value.

map . areas

Returns an HTMLCollection of the area elements in the map.

map . images

Returns an HTMLCollection of the img and object elements that use the map.

The areas attribute must return an HTMLCollection rooted at the map element, whose filter matches only area elements.

The images attribute must return an HTMLCollection rooted at the Document node, whose filter matches only img and object elements that are associated with this map element according to the image map processing model.

The DOM attribute name must reflect the content attribute of the same name.

4.8.13 The area element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected, but only if there is a map element ancestor.
Content model:
Empty.
Content attributes:
Global attributes
alt
coords
shape
href
target
ping
rel
media
hreflang
type
DOM interface:
[Stringifies=href] interface HTMLAreaElement : HTMLElement {
           attribute DOMString alt;
           attribute DOMString coords;
           attribute DOMString shape;
           attribute DOMString href;
           attribute DOMString target;
           attribute DOMString ping;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;

  // URL decomposition attributes
           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;
};

The area element represents either a hyperlink with some text and a corresponding area on an image map, or a dead area on an image map.

If the area element has an href attribute, then the area element represents a hyperlink. In this case, the alt attribute must be present. It specifies the text of the hyperlink. Its value must be text that, when presented with the texts specified for the other hyperlinks of the image map, and with the alternative text of the image, but without the image itself, provides the user with the same kind of choice as the hyperlink would when used without its text but with its shape applied to the image. The alt attribute may be left blank if there is another area element in the same image map that points to the same resource and has a non-blank alt attribute.

If the area element has no href attribute, then the area represented by the element cannot be selected, and the alt attribute must be omitted.

In both cases, the shape and coords attributes specify the area.

The shape attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the rows with keywords give the states to which those keywords map. Some of the keywords are non-conforming, as noted in the last column.

State Keywords Notes
Circle state circle
circ Non-conforming
Default state default
Polygon state poly
polygon Non-conforming
Rectangle state rect
rectangle Non-conforming

The attribute may be omitted. The missing value default is the rectangle state.

The coords attribute must, if specified, contain a valid list of integers. This attribute gives the coordinates for the shape described by the shape attribute. The processing for this attribute is described as part of the image map processing model.

In the circle state, area elements must have a coords attribute present, with three integers, the last of which must be non-negative. The first integer must be the distance in CSS pixels from the left edge of the image to the center of the circle, the second integer must be the distance in CSS pixels from the top edge of the image to the center of the circle, and the third integer must be the radius of the circle, again in CSS pixels.

In the default state state, area elements must not have a coords attribute. (The area is the whole image.)

In the polygon state, area elements must have a coords attribute with at least six integers, and the number of integers must be even. Each pair of integers must represent a coordinate given as the distances from the left and the top of the image in CSS pixels respectively, and all the coordinates together must represent the points of the polygon, in order.

In the rectangle state, area elements must have a coords attribute with exactly four integers, the first of which must be less than the third, and the second of which must be less than the fourth. The four points must represent, respectively, the distance from the left edge of the image to the left side of the rectangle, the distance from the top edge to the top side, the distance from the left edge to the right side, and the distance from the top edge to the bottom side, all in CSS pixels.

When user agents allow users to follow hyperlinks created using the area element, as described in the next section, the href, target and ping attributes decide how the link is followed. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

The target, ping, rel, media, hreflang, and type attributes must be omitted if the href attribute is not present.

The activation behavior of area elements is to run the following steps:

  1. If the DOMActivate event in question is not trusted (i.e. a click() method call was the reason for the event being dispatched), and the area element's target attribute is ... then raise an INVALID_ACCESS_ERR exception.
  2. Otherwise, the user agent must follow the hyperlink defined by the area element, if any.

The DOM attributes alt, coords, href, target, ping, rel, media, hreflang, and type, each must reflect the respective content attributes of the same name.

The DOM attribute shape must reflect the shape content attribute, limited to only known values.

The DOM attribute relList must reflect the rel content attribute.

The area element also suports the complement of URL decomposition attributes, protocol, host, port, hostname, pathname, search, and hash. These must follow the rules given for URL decomposition attributes, with the input being the result of resolving the element's href attribute relative to the element, if there is such an attribute and resolving it is successful, or the empty string otherwise; and the common setter action being the same as setting the element's href attribute to the new output value.

4.8.14 Image maps

4.8.14.1 Authoring

An image map allows geometric areas on an image to be associated with hyperlinks.

An image, in the form of an img element or an object element representing an image, may be associated with an image map (in the form of a map element) by specifying a usemap attribute on the img or object element. The usemap attribute, if specified, must be a valid hash-name reference to a map element.

Consider an image that looks as follows:

A line with four shapes in it, equally spaced: a red hollow box, a green circle, a blue triangle, and a yellow four-pointed star.

If we wanted just the colored areas to be clickable, we could do it as follows:

<p>
 Please select a shape:
 <img src="shapes.png" usemap="#shapes"
      alt="Four shapes are available: a red hollow box, a green circle, a blue triangle, and a yellow four-pointed star.">
 <map name="shapes">
  <area shape=rect coords="50,50,100,100"> <!-- the hole in the red box -->
  <area shape=rect coords="25,25,125,125" href="red.html" alt="Red box.">
  <area shape=circle coords="200,75,50" href="green.html" alt="Green circle.">
  <area shape=poly coords="325,25,262,125,388,125" href="blue.html" alt="Blue triangle.">
  <area shape=poly coords="450,25,435,60,400,75,435,90,450,125,465,90,500,75,465,60"
        href="yellow.html" alt="Yellow star.">
 </map>
</p>
4.8.14.2 Processing model

If an img element or an object element representing an image has a usemap attribute specified, user agents must process it as follows:

  1. First, rules for parsing a hash-name reference to a map element must be followed. This will return either an element (the map) or null.

  2. If that returned null, then abort these steps. The image is not associated with an image map after all.

  3. Otherwise, the user agent must collect all the area elements that are descendants of the map. Let those be the areas.

Having obtained the list of area elements that form the image map (the areas), interactive user agents must process the list in one of two ways.

If the user agent intends to show the text that the img element represents, then it must use the following steps.

In user agents that do not support images, or that have images disabled, object elements cannot represent images, and thus this section never applies (the fallback content is shown instead). The following steps therefore only apply to img elements.

  1. Remove all the area elements in areas that have no href attribute.

  2. Remove all the area elements in areas that have no alt attribute, or whose alt attribute's value is the empty string, if there is another area element in areas with the same value in the href attribute and with a non-empty alt attribute.

  3. Each remaining area element in areas represents a hyperlink. Those hyperlinks should all be made available to the user in a manner associated with the text of the img.

    In this context, user agents may represent area and img elements with no specified alt attributes, or whose alt attributes are the empty string or some other non-visible text, in a user-agent-defined fashion intended to indicate the lack of suitable author-provided text.

If the user agent intends to show the image and allow interaction with the image to select hyperlinks, then the image must be associated with a set of layered shapes, taken from the area elements in areas, in reverse tree order (so the last specified area element in the map is the bottom-most shape, and the first element in the map, in tree order, is the top-most shape).

Each area element in areas must be processed as follows to obtain a shape to layer onto the image:

  1. Find the state that the element's shape attribute represents.

  2. Use the rules for parsing a list of integers to parse the element's coords attribute, if it is present, and let the result be the coords list. If the attribute is absent, let the coords list be the empty list.

  3. If the number of items in the coords list is less than the minimum number given for the area element's current state, as per the following table, then the shape is empty; abort these steps.

    State Minimum number of items
    Circle state 3
    Default state 0
    Polygon state 6
    Rectangle state 4
  4. Check for excess items in the coords list as per the entry in the following list corresponding to the shape attribute's state:

    Circle state
    Drop any items in the list beyond the third.
    Default state
    Drop all items in the list.
    Polygon state
    Drop the last item if there's an odd number of items.
    Rectangle state
    Drop any items in the list beyond the fourth.
  5. If the shape attribute represents the rectangle state, and the first number in the list is numerically less than the third number in the list, then swap those two numbers around.

  6. If the shape attribute represents the rectangle state, and the second number in the list is numerically less than the fourth number in the list, then swap those two numbers around.

  7. If the shape attribute represents the circle state, and the third number in the list is less than or equal to zero, then the shape is empty; abort these steps.

  8. Now, the shape represented by the element is the one described for the entry in the list below corresponding to the state of the shape attribute:

    Circle state

    Let x be the first number in coords, y be the second number, and r be the third number.

    The shape is a circle whose center is x CSS pixels from the left edge of the image and x CSS pixels from the top edge of the image, and whose radius is r pixels.

    Default state

    The shape is a rectangle that exactly covers the entire image.

    Polygon state

    Let xi be the (2i)th entry in coords, and yi be the (2i+1)th entry in coords (the first entry in coords being the one with index 0).

    Let the coordinates be (xi, yi), interpreted in CSS pixels measured from the top left of the image, for all integer values of i from 0 to (N/2)-1, where N is the number of items in coords.

    The shape is a polygon whose vertices are given by the coordinates, and whose interior is established using the even-odd rule. [GRAPHICS]

    Rectangle state

    Let x1 be the first number in coords, y1 be the second number, x2 be the third number, and y2 be the fourth number.

    The shape is a rectangle whose top-left corner is given by the coordinate (x1, y1) and whose bottom right corner is given by the coordinate (x2, y2), those coordinates being interpreted as CSS pixels from the top left corner of the image.

    For historical reasons, the coordinates must be interpreted relative to the displayed image, even if it stretched using CSS or the image element's width and height attributes.

Mouse clicks on an image associated with a set of layered shapes per the above algorithm must be dispatched to the top-most shape covering the point that the pointing device indicated (if any), and then, must be dispatched again (with a new Event object) to the image element itself. User agents may also allow individual area elements representing hyperlinks to be selected and activated (e.g. using a keyboard); events from this are not also propagated to the image.

Because a map element (and its area elements) can be associated with multiple img and object elements, it is possible for an area element to correspond to multiple focusable areas of the document.

Image maps are live; if the DOM is mutated, then the user agent must act as if it had rerun the algorithms for image maps.

4.8.15 MathML

The math element from the MathML namespace falls into the embedded content category for the purposes of the content models in this specification.

User agents must handle text other than inter-element whitespace found in MathML elements whose content models do not allow raw text by pretending for the purposes of MathML content models, layout, and rendering that that text is actually wrapped in an mtext element in the MathML namespace. (Such text is not, however, conforming.)

User agents must act as if any MathML element whose contents does not match the element's content model was replaced, for the purposes of MathML layout and rendering, by an merror element in the MathML namespace containing some appropriate error message.

To enable authors to use MathML tools that only accept MathML in its XML form, interactive HTML user agents are encouraged to provide a way to export any MathML fragment as a namespace-well-formed XML fragment.

4.8.16 SVG

The svg element from the SVG namespace falls into the embedded content category for the purposes of the content models in this specification.

To enable authors to use SVG tools that only accept SVG in its XML form, interactive HTML user agents are encouraged to provide a way to export any SVG fragment as a namespace-well-formed XML fragment.

When the SVG foreignObject element contains elements from the HTML namespace, such elements must all be flow content. [SVG]

The content model for title elements in the SVG namespace inside HTML documents is phrasing content. (This further constrains the requirements given in the SVG specification.)

4.8.17 Dimension attributes

Author requirements: The width and height attributes on img, iframe, embed, object, video, and, when their type attribute is in the Image Button state, input elements may be specified to give the dimensions of the visual content of the element (the width and height respectively, relative to the nominal direction of the output medium), in CSS pixels. The attributes, if specified, must have values that are valid non-negative integers.

The specified dimensions given may differ from the dimensions specified in the resource itself, since the resource may have a resolution that differs from the CSS pixel resolution. (On screens, CSS pixels have a resolution of 96ppi, but in general the CSS pixel resolution depends on the reading distance.) If both attributes are specified, then one of the following statements must be true:

The target ratio is the ratio of the intrinsic width to the intrinsic height in the resource. The specified width and specified height are the values of the width and height attributes respectively.

The two attributes must be omitted if the resource in question does not have both an intrinsic width and an intrinsic height.

If the two attributes are both zero, it indicates that the element is not intended for the user (e.g. it might be a part of a service to count page views).

The dimension attributes are not intended to be used to stretch the image.

User agent requirements: User agents are expected to use these attributes as hints for the rendering.

The width and height DOM attributes on the iframe, embed, object, and video elements must reflect the respective content attributes of the same name.

4.9 Tabular data

4.9.1 Introduction

This section is non-normative.

...examples, how to write tables accessibly, a brief mention of the table model, etc...

4.9.2 The table element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
In this order: optionally a caption element, followed by either zero or more colgroup elements, followed optionally by a thead element, followed optionally by a tfoot element, followed by either zero or more tbody elements or one or more tr elements, followed optionally by a tfoot element (but there can only be one tfoot element child in total).
Content attributes:
Global attributes
DOM interface:
interface HTMLTableElement : HTMLElement {
           attribute HTMLTableCaptionElement caption;
  HTMLElement createCaption();
  void deleteCaption();
           attribute HTMLTableSectionElement tHead;
  HTMLElement createTHead();
  void deleteTHead();
           attribute HTMLTableSectionElement tFoot;
  HTMLElement createTFoot();
  void deleteTFoot();
  readonly attribute HTMLCollection tBodies;
  HTMLElement createTBody();
  readonly attribute HTMLCollection rows;
  HTMLElement insertRow([Optional] in long index);
  void deleteRow(in long index);
};

The table element represents data with more than one dimension, in the form of a table.

The table element takes part in the table model.

Tables must not be used as layout aids. Historically, some Web authors have misused tables in HTML as a way to control their page layout. This usage is non-conforming, because tools attempting to extract tabular data from such documents would obtain very confusing results. In particular, users of accessibility tools like screen readers are likely to find it very difficult to navigate pages with tables used for layout.

There are a variety of alternatives to using HTML tables for layout, primarily using CSS positioning and CSS tables.

User agents that do table analysis on arbitrary content are encouraged to find heuristics to determine which tables actually contain data and which are merely being used for layout. This specification does not define a precise heuristic.

Tables have rows and columns given by their descendants. A table must not have an empty row or column, as described in the description of the table model.

If a table element has a summary attribute, the user agent may report the contents of that attribute to the user.

Authors are encouraged to use the caption element instead of the summary attribute.

table . caption [ = value ]

Returns the table's caption element.

Can be set, to replace the caption element. If the new value is not a caption element, throws a HIERARCHY_REQUEST_ERR exception.

caption = table . createCaption()

Ensures the table has a caption element, and returns it.

table . deleteCaption()

Ensures the table does not have a caption element.

table . tHead [ = value ]

Returns the table's thead element.

Can be set, to replace the thead element. If the new value is not a thead element, throws a HIERARCHY_REQUEST_ERR exception.

thead = table . createTHead()

Ensures the table has a thead element, and returns it.

table . deleteTHead()

Ensures the table does not have a thead element.

table . tFoot [ = value ]

Returns the table's tfoot element.

Can be set, to replace the tfoot element. If the new value is not a tfoot element, throws a HIERARCHY_REQUEST_ERR exception.

tfoot = table . createTFoot()

Ensures the table has a tfoot element, and returns it.

table . deleteTFoot()

Ensures the table does not have a tfoot element.

table . tBodies

Returns an HTMLCollection of the tbody elements of the table.

tbody = table . createTBody()

Creates a tbody element, inserts it into the table, and returns it.

table . rows

Returns an HTMLCollection of the tr elements of the table.

tr = table . insertRow(index)

Creates a tr element, along with a tbody if required, inserts them into the table at the position given by the argument, and returns the tr.

The position is relative to the rows in the table. The index −1 is equivalent to inserting at the end of the table.

If the given position is less than −1 or greater than the number of rows, throws an INDEX_SIZE_ERR exception.

table . deleteRow(index)

Removes the tr element with the given position in the table.

The position is relative to the rows in the table. The index −1 is equivalent to deleting the last row of the table.

If the given position is less than −1 or greater than the index of the last row, or if there are no rows, throws an INDEX_SIZE_ERR exception.

The caption DOM attribute must return, on getting, the first caption element child of the table element, if any, or null otherwise. On setting, if the new value is a caption element, the first caption element child of the table element, if any, must be removed, and the new value must be inserted as the first node of the table element. If the new value is not a caption element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createCaption() method must return the first caption element child of the table element, if any; otherwise a new caption element must be created, inserted as the first node of the table element, and then returned.

The deleteCaption() method must remove the first caption element child of the table element, if any.

The tHead DOM attribute must return, on getting, the first thead element child of the table element, if any, or null otherwise. On setting, if the new value is a thead element, the first thead element child of the table element, if any, must be removed, and the new value must be inserted immediately before the first element in the table element that is neither a caption element nor a colgroup element, if any, or at the end of the table otherwise. If the new value is not a thead element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createTHead() method must return the first thead element child of the table element, if any; otherwise a new thead element must be created and inserted immediately before the first element in the table element that is neither a caption element nor a colgroup element, if any, or at the end of the table otherwise, and then that new element must be returned.

The deleteTHead() method must remove the first thead element child of the table element, if any.

The tFoot DOM attribute must return, on getting, the first tfoot element child of the table element, if any, or null otherwise. On setting, if the new value is a tfoot element, the first tfoot element child of the table element, if any, must be removed, and the new value must be inserted immediately before the first element in the table element that is neither a caption element, a colgroup element, nor a thead element, if any, or at the end of the table if there are no such elements. If the new value is not a tfoot element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createTFoot() method must return the first tfoot element child of the table element, if any; otherwise a new tfoot element must be created and inserted immediately before the first element in the table element that is neither a caption element, a colgroup element, nor a thead element, if any, or at the end of the table if there are no such elements, and then that new element must be returned.

The deleteTFoot() method must remove the first tfoot element child of the table element, if any.

The tBodies attribute must return an HTMLCollection rooted at the table node, whose filter matches only tbody elements that are children of the table element.

The createTBody() method must create a new tbody element, insert it immediately after the last tbody element in the table element, if any, or at the end of the table element if the table element has no tbody element children, and then must return the new tbody element.

The rows attribute must return an HTMLCollection rooted at the table node, whose filter matches only tr elements that are either children of the table element, or children of thead, tbody, or tfoot elements that are themselves children of the table element. The elements in the collection must be ordered such that those elements whose parent is a thead are included first, in tree order, followed by those elements whose parent is either a table or tbody element, again in tree order, followed finally by those elements whose parent is a tfoot element, still in tree order.

The behavior of the insertRow(index) method depends on the state of the table. When it is called, the method must act as required by the first item in the following list of conditions that describes the state of the table and the index argument:

If index is less than −1 or greater than the number of elements in rows collection:
The method must raise an INDEX_SIZE_ERR exception.
If the rows collection has zero elements in it, and the table has no tbody elements in it:
The method must create a tbody element, then create a tr element, then append the tr element to the tbody element, then append the tbody element to the table element, and finally return the tr element.
If the rows collection has zero elements in it:
The method must create a tr element, append it to the last tbody element in the table, and return the tr element.
If index is missing, equal to −1, or equal to the number of items in rows collection:
The method must create a tr element, and append it to the parent of the last tr element in the rows collection. Then, the newly created tr element must be returned.
Otherwise:
The method must create a tr element, insert it immediately before the indexth tr element in the rows collection, in the same parent, and finally must return the newly created tr element.

When the deleteRow(index) method is called, the user agent must run the following steps:

  1. If index is equal to −1, then index must be set to the number if items in the rows collection, minus one.

  2. Now, if index is less than zero, or greater than or equal to the number of elements in the rows collection, the method must instead raise an INDEX_SIZE_ERR exception, and these steps must be aborted.

  3. Otherwise, the method must remove the indexth element in the rows collection from its parent.

4.9.3 The caption element

Categories
None.
Contexts in which this element may be used:
As the first element child of a table element.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The caption element represents the title of the table that is its parent, if it has a parent and that is a table element.

The caption element takes part in the table model.

The caption element should be included for any table where the reader might have difficulty understanding the content or where the table's structure would not be obvious to the user of a screen reader. The element's contents should describe what the purpose of the table is, along with any information that could be useful for understanding and using the table.

When a table element is in a figure element alone but for the figure's legend, the caption element should be omitted in favor of the legend.

Consider, for instance, the following table:

1 2 3 4 5 6
1 2 3 4 5 6 7
2 3 4 5 6 7 8
3 4 5 6 7 8 9
4 5 6 7 8 9 10
5 6 7 8 9 10 11
6 7 8 9 10 11 12

In the abstract, this table is not clear. However, with a caption giving the table's number (for reference in the main prose) and explaining its use, it makes more sense:

<caption>
<strong>Table 1.</strong>
This table shows the total score obtained from rolling two six-sided
dice. The first row represents the value of the first die, the first
column the value of the second die. The total is given in the cell
that corresponds to the values of the two dice.
</caption>

This provides the user with more context:

Table 1. This table shows the total score obtained from rolling two six-sided dice. The first row represents the value of the first die, the first column the value of the second die. The total is given in the cell that corresponds to the values of the two dice.
1 2 3 4 5 6
1 2 3 4 5 6 7
2 3 4 5 6 7 8
3 4 5 6 7 8 9
4 5 6 7 8 9 10
5 6 7 8 9 10 11
6 7 8 9 10 11 12

4.9.4 The colgroup element

Categories
None.
Contexts in which this element may be used:
As a child of a table element, after any caption elements and before any thead, tbody, tfoot, and tr elements.
Content model:
Zero or more col elements.
Content attributes:
Global attributes
span
DOM interface:
interface HTMLTableColElement : HTMLElement {
           attribute unsigned long span;
};

The colgroup element represents a group of one or more columns in the table that is its parent, if it has a parent and that is a table element.

If the colgroup element contains no col elements, then the element may have a span content attribute specified, whose value must be a valid non-negative integer greater than zero.

The colgroup element and its span attribute take part in the table model.

The span DOM attribute must reflect the respective content attribute of the same name. The value must be limited to only positive non-zero numbers.

4.9.5 The col element

Categories
None.
Contexts in which this element may be used:
As a child of a colgroup element that doesn't have a span attribute.
Content model:
Empty.
Content attributes:
Global attributes
span
DOM interface:

HTMLTableColElement, same as for colgroup elements. This interface defines one member, span.

If a col element has a parent and that is a colgroup element that itself has a parent that is a table element, then the col element represents one or more columns in the column group represented by that colgroup.

The element may have a span content attribute specified, whose value must be a valid non-negative integer greater than zero.

The col element and its span attribute take part in the table model.

The span DOM attribute must reflect the content attribute of the same name. The value must be limited to only positive non-zero numbers.

4.9.6 The tbody element

Categories
None.
Contexts in which this element may be used:
As a child of a table element, after any caption, colgroup, and thead elements, but only if there are no tr elements that are children of the table element.
Content model:
Zero or more tr elements
Content attributes:
Global attributes
DOM interface:
interface HTMLTableSectionElement : HTMLElement {
  readonly attribute HTMLCollection rows;
  HTMLElement insertRow([Optional] in long index);
  void deleteRow(in long index);
};

The HTMLTableSectionElement interface is also used for thead and tfoot elements.

The tbody element represents a block of rows that consist of a body of data for the parent table element, if the tbody element has a parent and it is a table.

The tbody element takes part in the table model.

tbody . rows

Returns an HTMLCollection of the tr elements of the table section.

tr = tbody . insertRow( [ index ] )

Creates a tr element, inserts it into the table section at the position given by the argument, and returns the tr.

The position is relative to the rows in the table section. The index −1, which is the default if the argument is omitted, is equivalent to inserting at the end of the table section.

If the given position is less than −1 or greater than the number of rows, throws an INDEX_SIZE_ERR exception.

tbody . deleteRow(index)

Removes the tr element with the given position in the table section.

The position is relative to the rows in the table section. The index −1 is equivalent to deleting the last row of the table section.

If the given position is less than −1 or greater than the index of the last row, or if there are no rows, throws an INDEX_SIZE_ERR exception.

The rows attribute must return an HTMLCollection rooted at the element, whose filter matches only tr elements that are children of the element.

The insertRow(index) method must, when invoked on an element table section, act as follows:

If index is less than −1 or greater than the number of elements in the rows collection, the method must raise an INDEX_SIZE_ERR exception.

If index is missing, equal to −1, or equal to the number of items in the rows collection, the method must create a tr element, append it to the element table section, and return the newly created tr element.

Otherwise, the method must create a tr element, insert it as a child of the table section element, immediately before the indexth tr element in the rows collection, and finally must return the newly created tr element.

The deleteRow(index) method must remove the indexth element in the rows collection from its parent. If index is less than zero or greater than or equal to the number of elements in the rows collection, the method must instead raise an INDEX_SIZE_ERR exception.

4.9.7 The thead element

Categories
None.
Contexts in which this element may be used:
As a child of a table element, after any caption, and colgroup elements and before any tbody, tfoot, and tr elements, but only if there are no other thead elements that are children of the table element.
Content model:
Zero or more tr elements
Content attributes:
Global attributes
DOM interface:
HTMLTableSectionElement, as defined for tbody elements.

The thead element represents the block of rows that consist of the column labels (headers) for the parent table element, if the thead element has a parent and it is a table.

The thead element takes part in the table model.

4.9.8 The tfoot element

Categories
None.
Contexts in which this element may be used:
As a child of a table element, after any caption, colgroup, and thead elements and before any tbody and tr elements, but only if there are no other tfoot elements that are children of the table element.
As a child of a table element, after any caption, colgroup, thead, tbody, and tr elements, but only if there are no other tfoot elements that are children of the table element.
Content model:
Zero or more tr elements
Content attributes:
Global attributes
DOM interface:
HTMLTableSectionElement, as defined for tbody elements.

The tfoot element represents the block of rows that consist of the column summaries (footers) for the parent table element, if the tfoot element has a parent and it is a table.

The tfoot element takes part in the table model.

4.9.9 The tr element

Categories
None.
Contexts in which this element may be used:
As a child of a thead element.
As a child of a tbody element.
As a child of a tfoot element.
As a child of a table element, after any caption, colgroup, and thead elements, but only if there are no tbody elements that are children of the table element.
Content model:
Zero or more td or th elements
Content attributes:
Global attributes
DOM interface:
interface HTMLTableRowElement : HTMLElement {
  readonly attribute long rowIndex;
  readonly attribute long sectionRowIndex;
  readonly attribute HTMLCollection cells;
  HTMLElement insertCell([Optional] in long index);
  void deleteCell(in long index);
};

The tr element represents a row of cells in a table.

The tr element takes part in the table model.

tr . rowIndex

Returns the position of the row in the table's rows list.

Returns −1 if the element isn't in a table.

tr . sectionRowIndex

Returns the position of the row in the table section's rows list.

Returns −1 if the element isn't in a table section.

tr . cells

Returns an HTMLCollection of the td and th elements of the row.

cell = tr . insertCell( [ index ] )

Creates a td element, inserts it into the table row at the position given by the argument, and returns the td.

The position is relative to the cells in the row. The index −1, which is the default if the argument is omitted, is equivalent to inserting at the end of the row.

If the given position is less than −1 or greater than the number of cells, throws an INDEX_SIZE_ERR exception.

tr . deleteCell(index)

Removes the td or th element with the given position in the row.

The position is relative to the cells in the row. The index −1 is equivalent to deleting the last cell of the row.

If the given position is less than −1 or greater than the index of the last cell, or if there are no cells, throws an INDEX_SIZE_ERR exception.

The rowIndex attribute must, if the element has a parent table element, or a parent tbody, thead, or tfoot element and a grandparent table element, return the index of the tr element in that table element's rows collection. If there is no such table element, then the attribute must return −1.

The sectionRowIndex attribute must, if the element has a parent table, tbody, thead, or tfoot element, return the index of the tr element in the parent element's rows collection (for tables, that's the rows collection; for table sections, that's the rows collection). If there is no such parent element, then the attribute must return −1.

The cells attribute must return an HTMLCollection rooted at the tr element, whose filter matches only td and th elements that are children of the tr element.

The insertCell(index) method must act as follows:

If index is less than −1 or greater than the number of elements in the cells collection, the method must raise an INDEX_SIZE_ERR exception.

If index is missing, equal to −1, or equal to the number of items in cells collection, the method must create a td element, append it to the tr element, and return the newly created td element.

Otherwise, the method must create a td element, insert it as a child of the tr element, immediately before the indexth td or th element in the cells collection, and finally must return the newly created td element.

The deleteCell(index) method must remove the indexth element in the cells collection from its parent. If index is less than zero or greater than or equal to the number of elements in the cells collection, the method must instead raise an INDEX_SIZE_ERR exception.

4.9.10 The td element

Categories
Sectioning root.
Contexts in which this element may be used:
As a child of a tr element.
Content model:
Flow content.
Content attributes:
Global attributes
colspan
rowspan
headers
DOM interface:
interface HTMLTableDataCellElement : HTMLTableCellElement {};

The td element represents a data cell in a table.

The td element and its colspan, rowspan, and headers attributes take part in the table model.

4.9.11 The th element

Categories
None.
Contexts in which this element may be used:
As a child of a tr element.
Content model:
Phrasing content.
Content attributes:
Global attributes
colspan
rowspan
headers
scope
DOM interface:
interface HTMLTableHeaderCellElement : HTMLTableCellElement {
           attribute DOMString scope;
};

The th element represents a header cell in a table.

The th element may have a scope content attribute specified. The scope attribute is an enumerated attribute with five states, four of which have explicit keywords:

The row keyword, which maps to the row state
The row state means the header cell applies to some of the subsequent cells in the same row(s).
The col keyword, which maps to the column state
The column state means the header cell applies to some of the subsequent cells in the same column(s).
The rowgroup keyword, which maps to the row group state
The row group state means the header cell applies to all the remaining cells in the row group. A th element's scope attribute must not be in the row group state if the element is not anchored in a row group.
The colgroup keyword, which maps to the column group state
The column group state means the header cell applies to all the remaining cells in the column group. A th element's scope attribute must not be in the column group state if the element is not anchored in a column group.
The auto state
The auto state makes the header cell apply to a set of cells selected based on context.

The scope attribute's missing value default is the auto state.

The th element and its colspan, rowspan, headers, and scope attributes take part in the table model.

The scope DOM attribute must reflect the content attribute of the same name.

4.9.12 Attributes common to td and th elements

The td and th elements may have a colspan content attribute specified, whose value must be a valid non-negative integer greater than zero.

The td and th elements may also have a rowspan content attribute specified, whose value must be a valid non-negative integer.

These attributes give the number of columns and rows respectively that the cell is to span. These attributes must not be used to overlap cells, as described in the description of the table model.


The td and th element may have a headers content attribute specified. The headers attribute, if specified, must contain a string consisting of an unordered set of unique space-separated tokens, each of which must have the value of an ID of a th element taking part in the same table as the td or th element (as defined by the table model).

A th element with ID id is said to be directly targeted by all td and th elements in the same table that have headers attributes whose values include as one of their tokens the ID id. A th element A is said to be targeted by a th or td element B if either A is directly targeted by B or if there exists an element C that is itself targeted by the element B and A is directly targeted by C.

A th element must not be targeted by itself.

The colspan, rowspan, and headers attributes take part in the table model.


The td and th elements implement interfaces that inherit from the HTMLTableCellElement interface:

interface HTMLTableCellElement : HTMLElement {
           attribute long colSpan;
           attribute long rowSpan;
           attribute DOMString headers;
  readonly attribute long cellIndex;
};
cell . cellIndex

Returns the position of the cell in the row's cells list.

Returns 0 if the element isn't in a row.

The colSpan DOM attribute must reflect the content attribute of the same name. The value must be limited to only positive non-zero numbers.

The rowSpan DOM attribute must reflect the content attribute of the same name. Its default value, which must be used if parsing the attribute as a non-negative integer returns an error, is also 1.

The headers DOM attribute must reflect the content attribute of the same name.

The cellIndex DOM attribute must, if the element has a parent tr element, return the index of the cell's element in the parent element's cells collection. If there is no such parent element, then the attribute must return 0.

4.9.13 Processing model

The various table elements and their content attributes together define the table model.

A table consists of cells aligned on a two-dimensional grid of slots with coordinates (x, y). The grid is finite, and is either empty or has one or more slots. If the grid has one or more slots, then the x coordinates are always in the range 0 ≤ x < xwidth, and the y coordinates are always in the range 0 ≤ y < yheight. If one or both of xwidth and yheight are zero, then the table is empty (has no slots). Tables correspond to table elements.

A cell is a set of slots anchored at a slot (cellx, celly), and with a particular width and height such that the cell covers all the slots with coordinates (x, y) where cellx ≤ x < cellx+width and celly ≤ y < celly+height. Cells can either be data cells or header cells. Data cells correspond to td elements, and header cells correspond to th elements. Cells of both types can have zero or more associated header cells.

It is possible, in certain error cases, for two cells to occupy the same slot.

A row is a complete set of slots from x=0 to x=xwidth-1, for a particular value of y. Rows correspond to tr elements.

A column is a complete set of slots from y=0 to y=yheight-1, for a particular value of x. Columns can correspond to col elements, but in the absence of col elements are implied.

A row group is a set of rows anchored at a slot (0, groupy) with a particular height such that the row group covers all the slots with coordinates (x, y) where 0 ≤ x < xwidth and groupy ≤ y < groupy+height. Row groups correspond to tbody, thead, and tfoot elements. Not every row is necessarily in a row group.

A column group is a set of columns anchored at a slot (groupx, 0) with a particular width such that the column group covers all the slots with coordinates (x, y) where groupx ≤ x < groupx+width and 0 ≤ y < yheight. Column groups correspond to colgroup elements. Not every column is necessarily in a column group.

Row groups cannot overlap each other. Similarly, column groups cannot overlap each other.

A cell cannot cover slots that are from two or more row groups. It is, however, possible for a cell to be in multiple column groups. All the slots that form part of one cell are part of zero or one row groups and zero or more column groups.

In addition to cells, columns, rows, row groups, and column groups, tables can have a caption element associated with them. This gives the table a heading, or legend.

A table model error is an error with the data represented by table elements and their descendants. Documents must not have table model errors.

4.9.13.1 Forming a table

To determine which elements correspond to which slots in a table associated with a table element, to determine the dimensions of the table (xwidth and yheight), and to determine if there are any table model errors, user agents must use the following algorithm:

  1. Let xwidth be zero.

  2. Let yheight be zero.

  3. Let pending tfoot elements be a list of tfoot elements, initially empty.

  4. Let the table be the table represented by the table element. The xwidth and yheight variables give the table's dimensions. The table is initially empty.

  5. If the table element has no children elements, then return the table (which will be empty), and abort these steps.

  6. Associate the first caption element child of the table element with the table. If there are no such children, then it has no associated caption element.

  7. Let the current element be the first element child of the table element.

    If a step in this algorithm ever requires the current element to be advanced to the next child of the table when there is no such next child, then the user agent must jump to the step labeled end, near the end of this algorithm.

  8. While the current element is not one of the following elements, advance the current element to the next child of the table:

  9. If the current element is a colgroup, follow these substeps:

    1. Column groups: Process the current element according to the appropriate case below:

      If the current element has any col element children

      Follow these steps:

      1. Let xstart have the value of xwidth.

      2. Let the current column be the first col element child of the colgroup element.

      3. Columns: If the current column col element has a span attribute, then parse its value using the rules for parsing non-negative integers.

        If the result of parsing the value is not an error or zero, then let span be that value.

        Otherwise, if the col element has no span attribute, or if trying to parse the attribute's value resulted in an error, then let span be 1.

      4. Increase xwidth by span.

      5. Let the last span columns in the table correspond to the current column col element.

      6. If current column is not the last col element child of the colgroup element, then let the current column be the next col element child of the colgroup element, and return to the step labeled columns.

      7. Let all the last columns in the table from x=xstart to x=xwidth-1 form a new column group, anchored at the slot (xstart, 0), with width xwidth-xstart, corresponding to the colgroup element.

      If the current element has no col element children
      1. If the colgroup element has a span attribute, then parse its value using the rules for parsing non-negative integers.

        If the result of parsing the value is not an error or zero, then let span be that value.

        Otherwise, if the colgroup element has no span attribute, or if trying to parse the attribute's value resulted in an error, then let span be 1.

      2. Increase xwidth by span.

      3. Let the last span columns in the table form a new column group, anchored at the slot (xwidth-span, 0), with width span, corresponding to the colgroup element.

    2. Advance the current element to the next child of the table.

    3. While the current element is not one of the following elements, advance the current element to the next child of the table:

    4. If the current element is a colgroup element, jump to the step labeled column groups above.

  10. Let ycurrent be zero.

  11. Let the list of downward-growing cells be an empty list.

  12. Rows: While the current element is not one of the following elements, advance the current element to the next child of the table:

  13. If the current element is a tr, then run the algorithm for processing rows, advance the current element to the next child of the table, and return to the step labeled rows.

  14. Run the algorithm for ending a row group.

  15. If the current element is a tfoot, then add that element to the list of pending tfoot elements, advance the current element to the next child of the table, and return to the step labeled rows.

  16. The current element is either a thead or a tbody.

    Run the algorithm for processing row groups.

  17. Advance the current element to the next child of the table.

  18. Return to the step labeled rows.

  19. End: For each tfoot element in the list of pending tfoot elements, in tree order, run the algorithm for processing row groups.

  20. If there exists a row or column in the table the table containing only slots that do not have a cell anchored to them, then this is a table model error.

  21. Return the table.

The algorithm for processing row groups, which is invoked by the set of steps above for processing thead, tbody, and tfoot elements, is:

  1. Let ystart have the value of yheight.

  2. For each tr element that is a child of the element being processed, in tree order, run the algorithm for processing rows.

  3. If yheight > ystart, then let all the last rows in the table from y=ystart to y=yheight-1 form a new row group, anchored at the slot with coordinate (0, ystart), with height yheight-ystart, corresponding to the element being processed.

  4. Run the algorithm for ending a row group.

The algorithm for ending a row group, which is invoked by the set of steps above when starting and ending a block of rows, is:

  1. While ycurrent is less than yheight, follow these steps:

    1. Run the algorithm for growing downward-growing cells.

    2. Increase ycurrent by 1.

  2. Empty the list of downward-growing cells.

The algorithm for processing rows, which is invoked by the set of steps above for processing tr elements, is:

  1. If yheight is equal to ycurrent, then increase yheight by 1. (ycurrent is never greater than yheight.)

  2. Let xcurrent be 0.

  3. Run the algorithm for growing downward-growing cells.

  4. If the tr element being processed has no td or th element children, then increase ycurrent by 1, abort this set of steps, and return to the algorithm above.

  5. Let current cell be the first td or th element in the tr element being processed.

  6. Cells: While xcurrent is less than xwidth and the slot with coordinate (xcurrent, ycurrent) already has a cell assigned to it, increase xcurrent by 1.

  7. If xcurrent is equal to xwidth, increase xwidth by 1. (xcurrent is never greater than xwidth.)

  8. If the current cell has a colspan attribute, then parse that attribute's value, and let colspan be the result.

    If parsing that value failed, or returned zero, or if the attribute is absent, then let colspan be 1, instead.

  9. If the current cell has a rowspan attribute, then parse that attribute's value, and let rowspan be the result.

    If parsing that value failed or if the attribute is absent, then let rowspan be 1, instead.

  10. If rowspan is zero, then let cell grows downward be true, and set rowspan to 1. Otherwise, let cell grows downward be false.

  11. If xwidth < xcurrent+colspan, then let xwidth be xcurrent+colspan.

  12. If yheight < ycurrent+rowspan, then let yheight be ycurrent+rowspan.

  13. Let the slots with coordinates (x, y) such that xcurrent ≤ x < xcurrent+colspan and ycurrent ≤ y < ycurrent+rowspan be covered by a new cell c, anchored at (xcurrent, ycurrent), which has width colspan and height rowspan, corresponding to the current cell element.

    If the current cell element is a th element, let this new cell c be a header cell; otherwise, let it be a data cell.

    To establish which header cells apply to the current cell element, use the algorithm for assigning header cells described in the next section.

    If any of the slots involved already had a cell covering them, then this is a table model error. Those slots now have two cells overlapping.

  14. If cell grows downward is true, then add the tuple {c, xcurrent, colspan} to the list of downward-growing cells.

  15. Increase xcurrent by colspan.

  16. If current cell is the last td or th element in the tr element being processed, then increase ycurrent by 1, abort this set of steps, and return to the algorithm above.

  17. Let current cell be the next td or th element in the tr element being processed.

  18. Return to the step labelled cells.

When the algorithms above require the user agent to run the algorithm for growing downward-growing cells, the user agent must, for each {cell, cellx, width} tuple in the list of downward-growing cells, if any, extend the cell cell so that it also covers the slots with coordinates (x, ycurrent), where cellx ≤ x < cellx+width.

4.9.13.2 Forming relationships between data cells and header cells

Each cell can be assigned zero or more header cells. The algorithm for assigning header cells to a cell principal cell is as follows.

  1. Let header list be an empty list of cells.

  2. Let (principalx, principaly) be the coordinate of the slot to which the principal cell is anchored.

  3. If the principal cell has a headers attribute specified
    1. Take the value of the principal cell's headers attribute and split it on spaces, letting id list be the list of tokens obtained.

    2. For each token in the id list, if the first element in the Document with an ID equal to the token is a cell in the same table, and that cell is not the principal cell, then add that cell to header list.

    If principal cell does not have a headers attribute specified
    1. Let principalwidth be the width of the principal cell.

    2. Let principalheight be the height of the principal cell.

    3. For each value of y from principaly to principaly+principalheight-1, run the internal algorithm for scanning and assigning header cells, with the principal cell, the header list, the initial coordinate (principalx,y), and the increments Δx=−1 and Δy=0.

    4. For each value of x from principalx to principalx+principalwidth-1, run the internal algorithm for scanning and assigning header cells, with the principal cell, the header list, the initial coordinate (x,principaly), and the increments Δx=0 and Δy=−1.

    5. If the principal cell is anchored in a row group, then add all header cells that are row group headers and are anchored in the same row group with an x-coordinate less than or equal to principalx+principalwidth-1 and a y-coordinate less than or equal to principaly+principalheight-1 to header list.

    6. If the principal cell is anchored in a column group, then add all header cells that are column group headers and are anchored in the same column group with an x-coordinate less than or equal to principalx+principalwidth-1 and a y-coordinate less than or equal to principaly+principalheight-1 to header list.

  4. Remove all the empty cells from the header list.

  5. Remove any duplicates from the header list.

  6. Assign the headers in the header list to the principal cell.

The internal algorithm for scanning and assigning header cells, given a principal cell, a header list, an initial coordinate (initialx, initialy), and Δx and Δy increments, is as follows:

  1. Let x equal initialx.

  2. Let y equal initialy.

  3. Let opaque headers be an empty list of cells.

  4. If principal cell is a header cell

    Let in header block be true, and let headers from current header block be a list of cells containing just the principal cell.

    Otherwise

    Let in header block be false and let headers from current header block be an empty list of cells.

  5. Loop: Increment x by Δx; increment y by Δy.

    For each invocation of this algorithm, one of Δx and Δy will be −1, and the other will be 0.

  6. If either x or y is less than 0, then abort this internal algorithm.

  7. If there is no cell covering slot (x, y), or if there is more than one cell covering slot (x, y), return to the substep marked loop.

  8. Let current cell be the cell covering slot (x, y).

  9. If current cell is a header cell
    1. Set in header block to true.

    2. Add current cell to headers from current header block.

    3. Let blocked be false.

    4. If Δx is 0

      If there are any cells in the opaque headers list anchored with the same x-coordinate as the current cell, and with the same width as current cell, then let blocked be true.

      If the current cell is not a column header, then let blocked be true.

      If Δy is 0

      If there is are any cells in the opaque headers list anchored with the same y-coordinate as the current cell, and with the same height as current cell, then let blocked be true.

      If the current cell is not a row header, then let blocked be true.

    5. If blocked is false, then add the current cell to the headers list.

    If current cell is a data cell and in header block is true

    Set in header block to false. Add all the cells in headers from current header block to the opaque headers list, and empty the headers from current header block list.

  10. Return to the step marked loop.

A header cell anchored at the slot with coordinate (x, y) with width width and height height is said to be a column header if any of the following conditions are true:

A header cell anchored at the slot with coordinate (x, y) with width width and height height is said to be a row header if any of the following conditions are true:

A header cell is said to be a column group header if its scope attribute is in the column group state.

A header cell is said to be a row group header if its scope attribute is in the row group state.

A cell is said to be an empty cell if it contains no elements and its text content, if any, consists only of White_Space characters.

4.10 Forms

Forms allow unscripted client-server interaction: given a form, a user can provide data, submit it to the server, and have the server act on it accordingly (e.g. returning the results of a search or calculation). The elements used in forms can also be used for user interaction with no associated submission mechanism, in conjunction with scripts.

Mostly for historical reasons, elements in this section fall into several overlapping (but subtly different) categories in addition to the usual ones like flow content, phrasing content, and interactive content.

A number of the elements are form-associated elements, which means they can have a form owner and, to expose this, have a form content attribute with a matching form DOM attribute.

The form-associated elements fall into several subcategories:

Submittable elements
Denotes elements that can be used for constructing the form data set when a form element is submitted.
Resettable elements
Denotes elements that can be affected when a form element is reset.
Listed
Denotes elements that are listed in the form.elements and fieldset.elements APIs.
Labelable
Denotes elements that can be associated with label elements.

In addition, some submittable elements can be, depending on their attributes, buttons. The prose below defines when an element is a button. Some buttons are specifically submit buttons.

The object element is also a form-associated element and can, with the use of a suitable plugin, partake in form submission.

4.10.1 The form element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no form element descendants.
Content attributes:
Global attributes
accept-charset
action
autocomplete
enctype
method
name
novalidate
target
DOM interface:
[Callable=namedItem]
interface HTMLFormElement : HTMLElement {
           attribute DOMString acceptCharset;
           attribute DOMString action;
           attribute boolean autocomplete;
           attribute DOMString enctype;
           attribute DOMString method;
           attribute DOMString name;
           attribute boolean novalidate;
           attribute DOMString target;

  readonly attribute HTMLFormControlsCollection elements;
  readonly attribute long length;
  [IndexGetter] any item(in DOMString name);
  [NameGetter=OverrideBuiltins] any namedItem(in DOMString name);

  void submit();
  void reset();
  boolean checkValidity();

  void dispatchFormInput();
  void dispatchFormChange();
};

The form element represents a collection of form-associated elements, some of which can represent editable values that can be submitted to a server for processing.

The accept-charset attribute gives the character encodings that are to be used for the submission. If specified, the value must be an ordered set of unique space-separated tokens, and each token must be the preferred name of an ASCII-compatible character encoding. [IANACHARSET]

The name attribute represents the form's name within the forms collection. The value must not be the empty string, and the value must be unique amongst the form elements in the forms collection that it is in, if any.

The autocomplete attribute is an enumerated attribute. The attribute has two states. The on keyword maps to the on state, and the off keyword maps to the off state. The attribute may also be omitted. The missing value default is the on state. The off state indicates that by default, input elements in the form will have their resulting autocompletion state set to off; the on state indicates that by default, input elements in the form will have their resulting autocompletion state set to on.

The action, enctype, method, novalidate, and target attributes are attributes for form submission.

form . elements

Returns an HTMLCollection of the form controls in the form (excluding image buttons for historical reasons).

form . length

Returns the number of form controls in the form (excluding image buttons for historical reasons).

element = form . item(index)
form[index]

Returns the indexth element in the form (excluding image buttons for historical reasons).

element = form . namedItem(name)
form[name]

Returns the form control in the form with the given ID or name (excluding image buttons for historical reasons).

Once an element has been referenced using a particular name, that name will continue being available as a way to reference that element in this method, even if the element's actual ID or name changes, for as long as the element remains in the Document.

If there are multiple matching items, then a NodeList object containing all those elements is returned.

Returns null if no element with that ID or name could be found.

form . submit()

Submits the form.

form . reset()

Resets the form.

form . checkValidity()

Returns true if the form's controls are all valid; otherwise, returns false.

form . dispatchFormInput()

Dispatches a forminput event at all the form controls.

form . dispatchFormChange()

Dispatches a formchange event at all the form controls.

The autocomplete and name DOM attributes must reflect the respective content attributes of the same name.

The acceptCharset DOM attribute must reflect the accept-charset content attribute.


The elements DOM attribute must return an HTMLFormControlsCollection rooted at the Document node, whose filter matches listed elements whose form owner is the form element, with the exception of input elements whose type attribute is in the Image Button state, which must, for historical reasons, be excluded from this particular collection.

The length DOM attribute must return the number of nodes represented by the elements collection.

The indices of the supported indexed properties at any instant are the indices supported by the object returned by the elements attribute at that instant.

The item(index) method must return the value returned by the method of the same name on the elements collection, when invoked with the same argument.

Each form element has a mapping of names to elements called the past names map. It is used to persist names of controls even when they change names.

The names of the supported named properties are the union of the names currently supported by the object returned by the elements attribute, and the names currently in the past names map.

The namedItem(name) method, when called, must run the following steps:

  1. If name is one of the names of the supported named properties of the object returned by the elements attribute, then run these substeps:

    1. Let candidate be the object returned by the namedItem() method on the object returned by the elements attribute when passed the name argument.

    2. If candidate is an element, then add a mapping from name to candidate in the form element's past names map, replacing the previous entry with the same name, if any.

    3. Return candidate and abort these steps.

  2. Otherwise, name is the name of one of the entries in the form element's past names map: return the object associated with name in that map.

If an element listed in the form element's past names map is removed from the Document, then its entries must be removed from the map.


The submit() method, when invoked, must submit the form element from the form element itself.

The reset() method, when invoked, must reset the form element.

If the checkValidity() method is invoked, the user agent must statically validate the constraints of the form element, and return true if the constraint validation return a positive result, and false if it returned a negative result.

If the dispatchFormInput() method is invoked, the user agent must broadcast forminput events from the form element.

If the dispatchFormChange() method is invoked, the user agent must broadcast formchange events from the form element.

4.10.2 The fieldset element

Categories
Flow content.
Listed form-associated element.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
One legend element followed by flow content.
Content attributes:
Global attributes
disabled
form
name
DOM interface:
interface HTMLFieldSetElement : HTMLElement {
           attribute boolean disabled;
  readonly attribute HTMLFormElement form;
           attribute DOMString name;

  readonly attribute DOMString type;

  readonly attribute HTMLFormControlsCollection elements;

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);
};

The fieldset element represents a set of form controls grouped under a common name.

The name of the group is given by the first legend element that is a child of the fieldset element. The remainder of the descendants form the group.

The disabled attribute, when specified, causes all the form control descendants of the fieldset element to be disabled.

The form attribute is used to explicitly associate the fieldset element with its form owner. The name attribute represents the element's name.

fieldset . type

Returns the string "fieldset".

fieldset . elements

Returns an HTMLCollection of the form controls in the element.

The disabled DOM attribute must reflect the content attribute of the same name.

The type DOM attribute must return the string "fieldset".

The elements DOM attribute must return an HTMLFormControlsCollection rooted at the fieldset element, whose filter matches listed elements.

The willValidate, validity, and validationMessage attributes, and the checkValidity() and setCustomValidity() methods, are part of the constraint validation API.

Constraint validation: fieldset elements are always barred from constraint validation.

4.10.3 The label element

Categories
Flow content.
Phrasing content.
Interactive content.
Form-associated element.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content, but with no descendant labelable form-associated elements unless it is the element's labeled control, and no descendant label elements.
Content attributes:
Global attributes
form
for
DOM interface:
interface HTMLLabelElement : HTMLElement {
  readonly attribute HTMLFormElement form;
           attribute DOMString htmlFor;
  readonly attribute HTMLElement control;
};

The label represents a caption in a user interface. The caption can be associated with a specific form control, known as the label element's labeled control, either using for attribute, or by putting the form control inside the label element itself.

Unless otherwise specified by the following rules, a label element has no labeled control.

The for attribute may be specified to indicate a form control with which the caption is to be associated. If the attribute is specified, the attribute's value must be the ID of a labelable form-associated element in the same Document as the label element. If the attribute is specified and there is an element in the Document whose ID is equal to the value of the for attribute, and the first such element is a labelable form-associated element, then that element is the label element's labeled control.

If the for attribute is not specified, but the label element has a labelable form-associated element descendant, then the first such descendant in tree order is the label element's labeled control.

The label element's exact default presentation and behavior, in particular what its activation behavior might be, if anything, should match the platform's label behavior.

For example, on platforms where clicking a checkbox label checks the checkbox, clicking the label in the following snippet could trigger the user agent to run synthetic click activation steps on the input element, as if the element itself had been triggered by the user:

<label><input type=checkbox name=lost> Lost</label>

On other platforms, the behavior might be just to focus the control, or do nothing.

label . control

Returns the form control that is associated with this element.

The form attribute is used to explicitly associate the label element with its form owner.

The htmlFor DOM attribute must reflect the for content attribute.

The control DOM attribute must return the label element's labeled control, if any, or null if there isn't one.


control . labels

Returns a NodeList of all the label elements that the form control is associated with.

Labelable form-associated elements have a NodeList object associated with them that represents the list of label elements, in tree order, whose labeled control is the element in question. The labels DOM attribute of labelable form-associated elements, on getting, must return that NodeList object.

4.10.4 The input element

Categories
Flow content.
Phrasing content.
If the type attribute is not in the Hidden state: Interactive content.
Listed, labelable, submittable, and resettable form-associated element.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Empty.
Content attributes:
Global attributes
accept
alt
autocomplete
autofocus
checked
disabled
form
formaction
formenctype
formmethod
formnovalidate
formtarget
height
list
max
maxlength
min
multiple
name
pattern
placeholder
readonly
required
size
src
step
type
value
width
DOM interface:
interface HTMLInputElement : HTMLElement {
           attribute DOMString accept;
           attribute DOMString alt;
           attribute boolean autocomplete;
           attribute boolean autofocus;
           attribute boolean defaultChecked;
           attribute boolean checked;
           attribute boolean disabled;
  readonly attribute HTMLFormElement form;
           attribute DOMString formAction;
           attribute DOMString formEnctype;
           attribute DOMString formMethod;
           attribute boolean formNoValidate;
           attribute DOMString formTarget;
           attribute DOMString height;
           attribute boolean indeterminate;
  readonly attribute HTMLElement list;
           attribute DOMString max;
           attribute long maxLength;
           attribute DOMString min;
           attribute boolean multiple;
           attribute DOMString name;
           attribute DOMString pattern;
           attribute DOMString placeholder;
           attribute boolean readOnly;
           attribute boolean required;
           attribute unsigned long size;
           attribute DOMString src;
           attribute DOMString step;
           attribute DOMString type;
           attribute DOMString defaultValue;
           attribute DOMString value;
           attribute Date valueAsDate;
           attribute float valueAsNumber;
  readonly attribute HTMLOptionElement selectedOption;
           attribute DOMString width;

  void stepUp(in long n);
  void stepDown(in long n);

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);

  readonly attribute NodeList labels;

  void select();
           attribute unsigned long selectionStart;
           attribute unsigned long selectionEnd;
  void setSelectionRange(in unsigned long start, in unsigned long end);
};

The input element represents a typed data field, usually with a form control to allow the user to edit the data.

The type attribute controls the data type (and associated control) of the element. It is an enumerated attribute. The following table lists the keywords and states for the attribute — the keywords in the left column map to the states in the cell in the second column on the same row as the keyword.

Keyword State Data type Control type
hidden Hidden An arbitrary string n/a
text Text Text with no line breaks Text field
search Search Text with no line breaks Search field
url URL An absolute IRI A text field
email E-mail An e-mail address or list of e-mail addresses A text field
password Password Text with no line breaks (sensitive information) Text field that obscures data entry
datetime Date and Time A date and time (year, month, day, hour, minute, second, fraction of a second) with the time zone set to UTC A date and time control
date Date A date (year, month, day) with no time zone A date control
month Month A date consisting of a year and a month with no time zone A month control
week Week A date consisting of a week-year number and a week number with no time zone A week control
time Time A time (hour, minute, seconds, fractional seconds) with no time zone A time control
datetime-local Local Date and Time A date and time (year, month, day, hour, minute, second, fraction of a second) with no time zone A date and time control
number Number A numerical value A text field or spinner control
range Range A numerical value, with the extra semantic that the exact value is not important A slider control or similar
color Color An sRGB color with 8-bit red, green, and blue components A color well
checkbox Checkbox A set of zero or more values from a predefined list A checkbox
radio Radio Button An enumerated value A radio button
file File Upload Zero or more files each with a MIME type and optionally a file name A label and a button
submit Submit Button An enumerated value, with the extra semantic that it must be the last value selected and initiates form submission A button
image Image Button A coordinate, relative to a particular image's size, with the extra semantic that it must be the last value selected and initiates form submission Either a clickable image, or a button
reset Reset Button n/a A button
button Button n/a A button

The missing value default is the Text state.

Which of the accept, alt, autocomplete, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, maxlength, min, multiple, pattern, readonly, required, size, src, step, and width attributes apply to an input element depends on the state of its type attribute. Similarly, the checked, valueAsDate, valueAsNumber, list, and selectedOption DOM attributes, and the stepUp() and stepDown() methods, are specific to certain states. The following table is non-normative and summarises which content attributes, DOM attributes, and methods apply to each state:

Hidden Text, Search, URL E-mail Password Date and Time, Date, Month, Week, Time Local Date and Time, Number Range Color Checkbox, Radio Button File Upload Submit Button Image Button Reset Button, Button
accept · · · · · · · · · Yes · · ·
alt · · · · · · · · · · · Yes ·
autocomplete · Yes Yes Yes Yes Yes Yes Yes · · · · ·
checked · · · · · · · · Yes · · · ·
formaction · · · · · · · · · · Yes Yes ·
formenctype · · · · · · · · · · Yes Yes ·
formmethod · · · · · · · · · · Yes Yes ·
formnovalidate · · · · · · · · · · Yes Yes ·
formtarget · · · · · · · · · · Yes Yes ·
height · · · · · · · · · · · Yes ·
list · Yes Yes · Yes Yes Yes Yes · · · · ·
max · · · · Yes Yes Yes · · · · · ·
maxlength · Yes Yes Yes · · · · · · · · ·
min · · · · Yes Yes Yes · · · · · ·
multiple · · Yes · · · · · · Yes · · ·
pattern · Yes Yes Yes · · · · · · · · ·
placeholder · Yes Yes Yes · · · · · · · · ·
readonly · Yes Yes Yes Yes Yes · · · · · · ·
required · Yes Yes Yes Yes Yes · · Yes Yes · · ·
size · Yes Yes Yes · · · · · · · · ·
src · · · · · · · · · · · Yes ·
step · · · · Yes Yes Yes · · · · · ·
width · · · · · · · · · · · Yes ·
checked · · · · · · · · Yes · · · ·
value value value value value value value value value default/on filename default default default
valueAsDate · · · · Yes · · · · · · · ·
valueAsNumber · · · · Yes Yes Yes · · · · · ·
list · Yes Yes · Yes Yes Yes Yes · · · · ·
selectedOption · Yes Yes · Yes Yes Yes Yes · · · · ·
select() · Yes Yes Yes · · · · · · · · ·
selectionStart · Yes Yes Yes · · · · · · · · ·
selectionEnd · Yes Yes Yes · · · · · · · · ·
setSelectionRange() · Yes Yes Yes · · · · · · · · ·
stepDown() · · · · Yes Yes Yes · · · · · ·
stepUp() · · · · Yes Yes Yes · · · · · ·
input event · Yes Yes Yes Yes Yes Yes Yes Yes · · · ·
change event · Yes Yes Yes Yes Yes Yes Yes Yes Yes · · ·

When an input element's type attribute changes state, and when the element is first created, the element's rendering and behavior must change to the new state's accordingly and the value sanitization algorithm, if one is defined for the type attribute's new state, must be invoked.

Each input element has a value, which is exposed by the value DOM attribute. Some states define an algorithm to convert a string to a number, an algorithm to convert a number to a string, an algorithm to convert a string to a Date object, and an algorithm to convert a Date object to a string, which are used by max, min, step, valueAsDate, valueAsNumber, stepDown(), and stepUp().

Each input element has a boolean dirty value flag. When it is true, the element is said to have a dirty value. The dirty value flag must be initially set to false when the element is created, and must be set to true whenever the user interacts with the control in a way that changes the value.

The value content attribute gives the default value of the input element. When the value content attribute is added, set, or removed, if the control does not have a dirty value, the user agent must set the value of the element to the value of the value content attribute, if there is one, or the empty string otherwise, and then run the current value sanitization algorithm, if one is defined.

Each input element has a checkedness, which is exposed by the checked DOM attribute.

Each input element has a boolean dirty checkedness flag. When it is true, the element is said to have a dirty checkedness. The dirty checkedness flag must be initially set to false when the element is created, and must be set to true whenever the user interacts with the control in a way that changes the checkedness.

The checked content attribute gives the default checkedness of the input element. When the checked content attribute is added, if the control does not have dirty checkedness, the user agent must set the checkedness of the element to true; when the checked content attribute is removed, if the control does not have dirty checkedness, the user agent must set the checkedness of the element to false.

The reset algorithm for input elements is to set the dirty value flag and dirty checkedness flag back to false, set the value of the element to the value of the value content attribute, if there is one, or the empty string otherwise, set the checkedness of the element to true if the element has a checked content attribute and false if it does not, and then invoke the value sanitization algorithm, if the type attribute's current state defines one.

Each input element has a boolean mutability flag. When it is true, the element is said to be mutable, and when it is false the element is immutable. Unless otherwise specified, an input element is always mutable. Unless otherwise specified, the user agent should not allow the user to modify the element's value or checkedness.

When an input element is disabled, it is immutable.

When an input element does not have a Document node as one of its ancestors (i.e. when it is not in the document), it is immutable.

The readonly attribute can also in some cases (e.g. for the Date state, but not the Checkbox state) make an input element immutable.

The form attribute is used to explicitly associate the input element with its form owner. The name attribute represents the element's name. The disabled attribute is used to make the control non-interactive and to prevent its value from being submitted. The autofocus attribute controls focus.

The indeterminate DOM attribute must initially be set to false. On getting, it must return the last value it was set to. On setting, it must be set to the new value. It has no effect except for changing the appearance of checkbox controls.

The accept, alt, autocomplete, max, min, multiple, pattern, placeholder, required, size, src, step, and type DOM attributes must reflect the respective content attributes of the same name. The maxLength DOM attribute must reflect the maxlength content attribute. The readOnly DOM attribute must reflect the readonly content attribute. The defaultChecked DOM attribute must reflect the checked content attribute. The defaultValue DOM attribute must reflect the value content attribute.

The willValidate, validity, and validationMessage attributes, and the checkValidity() and setCustomValidity() methods, are part of the constraint validation API. The labels attribute provides a list of the element's labels. The select(), selectionStart, selectionEnd, and setSelectionRange() methods and attributes expose the element's text selection.

4.10.4.1 States of the type attribute
4.10.4.1.1 Hidden state

When an input element's type attribute is in the Hidden state, the rules in this section apply.

The input element represents a value that is not intended to be examined or manipulated by the user.

Constraint validation: If an input element's type attribute is in the Hidden state, it is barred from constraint validation.

If the name attribute is present and has a value that is a case-sensitive match for the string "_charset_", then the element's value attribute must be omitted.

The value DOM attribute applies to this element and is in mode value.

The following content attributes must not be specified and do not apply to the element: accept, alt, autocomplete, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, maxlength, min, multiple, pattern, placeholder, readonly, required, size, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, list, selectedOption, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

The input and change events do not apply.

4.10.4.1.2 Text state and Search state

When an input element's type attribute is in the Text state or the Search state, the rules in this section apply.

The input element represents a one line plain text edit control for the element's value.

If the element is mutable, its value should be editable by the user. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the element's value.

The value attribute, if specified, must have a value that contains no U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters.

The value sanitization algorithm is as follows: Strip line breaks from the value.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, maxlength, pattern, placeholder, readonly, required, and size content attributes; list, selectedOption, selectionStart, selectionEnd, and value DOM attributes; select() and setSelectionRange() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, max, min, multiple, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, valueAsDate, and valueAsNumber DOM attributes; stepDown() and stepUp() methods.

4.10.4.1.3 URL state

When an input element's type attribute is in the URL state, the rules in this section apply.

The input element represents a control for editing a single absolute URL given in the element's value.

If the is mutable, the user agent should allow the user to change the URL represented by its value. User agents may allow the user to set the value to a string that is not a valid absolute URL, but may also or instead automatically escape characters entered by the user so that the value is always a valid absolute URL (even if that isn't the actual value seen and edited by the user in the interface). User agents should allow the user to set the value to the empty string. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the value.

The value attribute, if specified, must have a value that is a valid absolute URL.

The value sanitization algorithm is as follows: Strip line breaks from the value.

Constraint validation: While the value of the element is not a valid absolute URL, the element is suffering from a type mismatch.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, maxlength, pattern, placeholder, readonly, required, and size content attributes; list, selectedOption, selectionStart, selectionEnd, and value DOM attributes; select() and setSelectionRange() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, max, min, multiple, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, valueAsDate, and valueAsNumber DOM attributes; stepDown() and stepUp() methods.

4.10.4.1.4 E-mail state

When an input element's type attribute is in the E-mail state, the rules in this section apply.

The input element represents a control for editing a list of e-mail addresses given in the element's value.

If the element is mutable, the user agent should allow the user to change the e-mail addresses represented by its value. If the multiple attribute is specified, then the user agent should allow the user to select or provide multiple addresses; otherwise, the user agent should act in a manner consistent with expecting the user to provide a single e-mail address. User agents may allow the user to set the value to a string that is not an valid e-mail address list. User agents should allow the user to set the value to the empty string. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the value. User agents may transform the value for display and editing (e.g. converting punycode in the value to IDN in the display and vice versa).

If the multiple attribute is specified on the element, then the value attribute, if specified, must have a value that is a valid e-mail address list; otherwise, the value attribute, if specified, must have a value that is a single valid e-mail address.

The value sanitization algorithm is as follows: Strip line breaks from the value.

Constraint validation: If the multiple attribute is specified on the element, then, while the value of the element is not a valid e-mail address list, the element is suffering from a type mismatch; otherwise, while the value of the element is not a single valid e-mail address, the element is suffering from a type mismatch.

A valid e-mail address list is a set of comma-separated tokens, where each token is itself a valid e-mail address. To obtain the list of tokens from a valid e-mail address list, the user agent must split the string on commas.

A valid e-mail address is a string that matches the production dot-atom "@" dot-atom where dot-atom is defined in RFC 2822 section 3.2.4, excluding the CFWS production everywhere. [RFC2822]

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, maxlength, multiple, pattern, placeholder, readonly, required, and size content attributes; list, selectedOption, selectionStart, selectionEnd, and value DOM attributes; select() and setSelectionRange() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, max, min, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, valueAsDate, and valueAsNumber DOM attributes; stepDown() and stepUp() methods.

4.10.4.1.5 Password state

When an input element's type attribute is in the Password state, the rules in this section apply.

The input element represents a one line plain text edit control for the element's value. The user agent should obscure the value so that people other than the user cannot see it.

If the element is mutable, its value should be editable by the user. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the value.

The value attribute, if specified, must have a value that contains no U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters.

The value sanitization algorithm is as follows: Strip line breaks from the value.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, maxlength, pattern, placeholder, readonly, required, and size content attributes; selectionStart, selectionEnd, and value DOM attributes; select(), and setSelectionRange() methods.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, min, multiple, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, list, selectedOption, valueAsDate, and valueAsNumber DOM attributes; stepDown() and stepUp() methods.

4.10.4.1.6 Date and Time state

When an input element's type attribute is in the Date and Time state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific global date and time. User agents may display the date and time in whatever time zone is appropriate for the user.

If the element is mutable, the user agent should allow the user to change the global date and time represented by its value, as obtained by parsing a global date and time from it. User agents must not allow the user to set the value to a string that is not a valid global date and time string expressed in UTC, though user agents may allow the user to set and view the time in another time zone and silently translate the time to and from the UTC time zone in the value. If the user agent provides a user interface for selecting a global date and time, then the value must be set to a valid global date and time string expressed in UTC representing the user's selection. User agents should allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid global date and time string.

The value sanitization algorithm is as follows: If the value of the element is a valid global date and time string, then adjust the time so that the value represents the same point in time but expressed in the UTC time zone, otherwise, set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid global date and time string. The max attribute, if specified, must have a value that is a valid global date and time string.

The step attribute is expressed in seconds. The step scale factor is 1000 (which converts the seconds to milliseconds, as used in the other algorithms). The default step is 60 seconds.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest global date and time for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a global date and time from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z") to the parsed global date and time, ignoring leap seconds.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid global date and time string expressed in UTC that represents the global date and time that is input milliseconds after midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z").

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a global date and time from input results in an error, then return an error; otherwise, return a Date object representing the parsed global date and time, expressed in UTC.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid global date and time string expressed in UTC that represents the global date and time that is represented by input.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, max, min, readonly, required, and step content attributes; list, value, valueAsDate, valueAsNumber, and selectedOption DOM attributes; stepDown() and stepUp() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, multiple, pattern, placeholder, size, src, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, and selectionEnd DOM attributes; select() and setSelectionRange() methods.

4.10.4.1.7 Date state

When an input element's type attribute is in the Date state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific date.

If the element is mutable, the user agent should allow the user to change the date represented by its value, as obtained by parsing a date from it. User agents must not allow the user to set the value to a string that is not a valid date string. If the user agent provides a user interface for selecting a date, then the value must be set to a valid date string representing the user's selection. User agents should allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid date string.

The value sanitization algorithm is as follows: If the value of the element is not a valid date string, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid date string. The max attribute, if specified, must have a value that is a valid date string.

The step attribute is expressed in days. The step scale factor is 86,400,000 (which converts the days to milliseconds, as used in the other algorithms). The default step is 1 day.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest date for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a date from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z") to midnight UTC on the morning of the parsed date, ignoring leap seconds.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid date string that represents the date that, in UTC, is current input milliseconds after midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z").

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a date from input results in an error, then return an error; otherwise, return a Date object representing midnight UTC on the morning of the parsed date.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid date string that represents the date current at the time represented by input in the UTC time zone.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, max, min, readonly, required, and step content attributes; list, value, valueAsDate, valueAsNumber, and selectedOption DOM attributes; stepDown() and stepUp() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, multiple, pattern, placeholder, size, src, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, and selectionEnd DOM attributes; select() and setSelectionRange() methods.

4.10.4.1.8 Month state

When an input element's type attribute is in the Month state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific month.

If the element is mutable, the user agent should allow the user to change the month represented by its value, as obtained by parsing a month from it. User agents must not allow the user to set the value to a string that is not a valid month string. If the user agent provides a user interface for selecting a month, then the value must be set to a valid month string representing the user's selection. User agents should allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid month string.

The value sanitization algorithm is as follows: If the value of the element is not a valid month string, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid month string. The max attribute, if specified, must have a value that is a valid month string.

The step attribute is expressed in months. The step scale factor is 1 (there is no conversion needed as the algorithms use months). The default step is 1 month.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest month for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a month time from input results in an error, then return an error; otherwise, return the number of months between January 1970 and the parsed month.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid month string that represents the month that has input months between it and January 1970.

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a month from input results in an error, then return an error; otherwise, return a Date object representing midnight UTC on the morning of the first day of the parsed month.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid month string that represents the month current at the time represented by input in the UTC time zone.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, max, min, readonly, required, and step content attributes; list, value, valueAsDate, valueAsNumber, and selectedOption DOM attributes; stepDown() and stepUp() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, multiple, pattern, placeholder, size, src, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, and selectionEnd DOM attributes; select() and setSelectionRange() methods.

4.10.4.1.9 Week state

When an input element's type attribute is in the Week state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific week.

If the element is mutable, the user agent should allow the user to change the week represented by its value, as obtained by parsing a week from it. User agents must not allow the user to set the value to a string that is not a valid week string. If the user agent provides a user interface for selecting a week, then the value must be set to a valid week string representing the user's selection. User agents should allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid week string.

The value sanitization algorithm is as follows: If the value of the element is not a valid week string, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid week string. The max attribute, if specified, must have a value that is a valid week string.

The step attribute is expressed in weeks. The step scale factor is 604,800,000 (which converts the weeks to milliseconds, as used in the other algorithms). The default step is 1 week.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest week for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a week string from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z") to midnight UTC on the morning of the Monday of the parsed week, ignoring leap seconds.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid week string that represents the week that, in UTC, is current input milliseconds after midnight UTC on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z").

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a week from input results in an error, then return an error; otherwise, return a Date object representing midnight UTC on the morning of the Monday of the parsed week.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid week string that represents the week current at the time represented by input in the UTC time zone.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, max, min, readonly, required, and step content attributes; list, value, valueAsDate, valueAsNumber, and selectedOption DOM attributes; stepDown() and stepUp() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, multiple, pattern, placeholder, size, src, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, and selectionEnd DOM attributes; select() and setSelectionRange() methods.

4.10.4.1.10 Time state

When an input element's type attribute is in the Time state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a specific time.

If the element is mutable, the user agent should allow the user to change the time represented by its value, as obtained by parsing a time from it. User agents must not allow the user to set the value to a string that is not a valid time string. If the user agent provides a user interface for selecting a time, then the value must be set to a valid time string representing the user's selection. User agents should allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid time string.

The value sanitization algorithm is as follows: If the value of the element is not a valid time string, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid time string. The max attribute, if specified, must have a value that is a valid time string.

The step attribute is expressed in seconds. The step scale factor is 1000 (which converts the seconds to milliseconds, as used in the other algorithms). The default step is 60 seconds.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest time for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a time from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight to the parsed time on a day with no time changes.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid time string that represents the time that is input milliseconds after midnight on a day with no time changes.

The algorithm to convert a string to a Date object, given a string input, is as follows: If parsing a time from input results in an error, then return an error; otherwise, return a Date object representing the parsed time in UTC on 1970-01-01.

The algorithm to convert a Date object to a string, given a Date object input, is as follows: Return a valid time string that represents the UTC time component that is represented by input.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, max, min, readonly, required, and step content attributes; list, value, valueAsDate, valueAsNumber, and selectedOption DOM attributes; stepDown() and stepUp() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, multiple, pattern, placeholder, size, src, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, and selectionEnd DOM attributes; select() and setSelectionRange() methods.

4.10.4.1.11 Local Date and Time state

When an input element's type attribute is in the Local Date and Time state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a local date and time, with no time zone information.

If the element is mutable, the user agent should allow the user to change the date and time represented by its value, as obtained by parsing a date and time from it. User agents must not allow the user to set the value to a string that is not a valid local date and time string. If the user agent provides a user interface for selecting a local date and time, then the value must be set to a valid local date and time string representing the user's selection. User agents should allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid local date and time string.

The value sanitization algorithm is as follows: If the value of the element is not a valid local date and time string, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid local date and time string. The max attribute, if specified, must have a value that is a valid local date and time string.

The step attribute is expressed in seconds. The step scale factor is 1000 (which converts the seconds to milliseconds, as used in the other algorithms). The default step is 60 seconds.

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest local date and time for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If parsing a date and time from input results in an error, then return an error; otherwise, return the number of milliseconds elapsed from midnight on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0") to the parsed local date and time, ignoring leap seconds.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid local date and time string that represents the date and time that is input milliseconds after midnight on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0").

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, max, min, readonly, required, and step content attributes; list, value, valueAsNumber, and selectedOption DOM attributes; stepDown() and stepUp() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, multiple, pattern, placeholder, size, src, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, selectionEnd, and valueAsDate DOM attributes; select() and setSelectionRange() methods.

4.10.4.1.12 Number state

When an input element's type attribute is in the Number state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a number.

If the element is mutable, the user agent should allow the user to change the number represented by its value, as obtained from applying the rules for parsing floating point number values to it. User agents must not allow the user to set the value to a string that is not a valid floating point number. If the user agent provides a user interface for selecting a number, then the value must be set to the best representation of the floating point number representing the user's selection. User agents should allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid floating point number.

The value sanitization algorithm is as follows: If the value of the element is not a valid floating point number, then set it to the empty string instead.

The min attribute, if specified, must have a value that is a valid floating point number. The max attribute, if specified, must have a value that is a valid floating point number.

The step scale factor is 1. The default step is 1 (allowing only integers, unless the min attribute has a non-integer value).

When the element is suffering from a step mismatch, the user agent may round the element's value to the nearest number for which the element would not suffer from a step mismatch.

The algorithm to convert a string to a number, given a string input, is as follows: If applying the rules for parsing floating point number values to input results in an error, then return an error; otherwise, return the resulting number.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid floating point number that represents input.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, max, min, readonly, required, and step content attributes; list, value, valueAsNumber, and selectedOption DOM attributes; stepDown() and stepUp() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, multiple, pattern, placeholder, size, src, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, selectionEnd, and valueAsDate DOM attributes; select() and setSelectionRange() methods.

4.10.4.1.13 Range state

When an input element's type attribute is in the Range state, the rules in this section apply.

The input element represents a control for setting the element's value to a string representing a number, but with the caveat that the exact value is not important, letting UAs provide a simpler interface than they do for the Number state.

In this state, the range and step constraints are enforced even during user input, and there is no way to set the value to the empty string.

If the element is mutable, the user agent should allow the user to change the number represented by its value, as obtained from applying the rules for parsing floating point number values to it. User agents must not allow the user to set the value to a string that is not a valid floating point number. If the user agent provides a user interface for selecting a number, then the value must be set to a best representation of the floating point number representing the user's selection. User agents must not allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid floating point number.

The value sanitization algorithm is as follows: If the value of the element is not a valid floating point number, then set it to a valid floating point number that represents the default value.

The min attribute, if specified, must have a value that is a valid floating point number. The default minimum is 0. The max attribute, if specified, must have a value that is a valid floating point number. The default maximum is 100.

The default value is the minimum plus half the difference between the minimum and the maximum, unless the maximum is less than the minimum, in which case the default value is the minimum.

When the element is suffering from an underflow, the user agent must set the element's value to a valid floating point number that represents the minimum.

When the element is suffering from an overflow, if the maximum is not less than the minimum, the user agent must set the element's value to a valid floating point number that represents the maximum.

The step scale factor is 1. The default step is 1 (allowing only integers, unless the min attribute has a non-integer value).

When the element is suffering from a step mismatch, the user agent must round the element's value to the nearest number for which the element would not suffer from a step mismatch, and which is greater than or equal to the minimum, and, if the maximum is not less than the minimum, which is less than or equal to the maximum.

The algorithm to convert a string to a number, given a string input, is as follows: If applying the rules for parsing floating point number values to input results in an error, then return an error; otherwise, return the resulting number.

The algorithm to convert a number to a string, given a number input, is as follows: Return a valid floating point number that represents input.

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete, list, max, min, and step content attributes; list, value, valueAsNumber, and selectedOption DOM attributes; stepDown() and stepUp() methods.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, multiple, pattern, placeholder, readonly, required, size, src, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, selectionEnd, and valueAsDate DOM attributes; select() and setSelectionRange() methods.

4.10.4.1.14 Color state

When an input element's type attribute is in the Color state, the rules in this section apply.

The input element represents a color well control, for setting the element's value to a string representing a simple color.

In this state, there is always a color picked, and there is no way to set the value to the empty string.

If the element is mutable, the user agent should allow the user to change the color represented by its value, as obtained from applying the rules for parsing simple color values to it. User agents must not allow the user to set the value to a string that is not a valid lowercase simple color. If the user agent provides a user interface for selecting a color, then the value must be set to the result of using the rules for serializing simple color values to the user's selection. User agents must not allow the user to set the value to the empty string.

The value attribute, if specified, must have a value that is a valid simple color.

The value sanitization algorithm is as follows: If the value of the element is a valid simple color, then set it to the value of the element converted to lowercase; otherwise, set it to the string "#000000".

The following common input element content attributes, DOM attributes, and methods apply to the element: autocomplete and list content attributes; list, value, and selectedOption DOM attributes.

The value DOM attribute is in mode value.

The input and change events apply.

The following content attributes must not be specified and do not apply to the element: accept, alt, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, max, min, multiple, pattern, placeholder, readonly, required, size, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

4.10.4.1.15 Checkbox state

When an input element's type attribute is in the Checkbox state, the rules in this section apply.

The input element represents a two-state control that represents the element's checkedness state. If the element's checkedness state is true, the control represents a positive selection, and if it is false, a negative selection. If the element's indeterminate DOM attribute is set to true, then the control's selection should be obscured as if the control was in a third, indeterminate, state.

The control is never a true tri-state control, even if the element's indeterminate DOM attribute is set to true. The indeterminate DOM attribute only gives the appearance of a third state.

If the element is mutable, then: The pre-click activation steps consist of setting the element's checkedness to its opposite value (i.e. true if it is false, false if it is true), and of setting the element's indeterminate DOM attribute to false. The canceled activation steps consist of setting the checkedness and the element's indeterminate DOM attribute back to the values they had before the pre-click activation steps were run. The activation behavior is to fire a simple event called change at the element, then broadcast formchange events at the element's form owner.

Constraint validation: If the element is required and its checkedness is false, then the element is suffering from being missing.

input . indeterminate [ = value ]

When set, overrides the rendering of checkbox controls so that the current value is not visible.

The following common input element content attributes and DOM attributes apply to the element: checked, and required content attributes; checked and value DOM attributes.

The value DOM attribute is in mode default/on.

The change event applies.

The following content attributes must not be specified and do not apply to the element: accept, alt, autocomplete, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, maxlength, min, multiple, pattern, placeholder, readonly, size, src, step, and width.

The following DOM attributes and methods do not apply to the element: list, selectedOption, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

The input event does not apply.

4.10.4.1.16 Radio Button state

When an input element's type attribute is in the Radio Button state, the rules in this section apply.

The input element represents a control that, when used in conjunction with other input elements, forms a radio button group in which only one control can have its checkedness state set to true. If the element's checkedness state is true, the control represents the selected control in the group, and if it is false, it indicates a control in the group that is not selected.

The radio button group that contains an input element a also contains all the other input elements b that fulfill all of the following conditions:

A document must not contain an input element whose radio button group contains only that element.

When any of the following events occur, if the element's checkedness state is true after the event, the checkedness state of all the other elements in the same radio button group must be set to false:

If the element is mutable, then: The pre-click activation steps consist of setting the element's checkedness to true. The canceled activation steps consist of setting the element's checkedness to false. The activation behavior is to fire a simple event called change at the element, then broadcast formchange events at the element's form owner.

Constraint validation: If the element is required and all of the input elements in the radio button group have a checkedness that is false, then the element is suffering from being missing.

If none of the radio buttons in a radio button group are checked when they are inserted into the document, then they will all be initially unchecked in the interface, until such time as one of them is checked (either by the user or by script).

The following common input element content attributes and DOM attributes apply to the element: checked and required content attributes; checked and value DOM attributes.

The value DOM attribute is in mode default/on.

The change event applies.

The following content attributes must not be specified and do not apply to the element: accept, alt, autocomplete, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, maxlength, min, multiple, pattern, placeholder, readonly, size, src, step, and width.

The following DOM attributes and methods do not apply to the element: list, selectedOption, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

The input event does not apply.

4.10.4.1.17 File Upload state

When an input element's type attribute is in the File Upload state, the rules in this section apply.

The input element represents a list of selected files, each file consisting of a file name, a file type, and a file body (the contents of the file).

If the element is mutable, the user agent should allow the user to change the files on the list, e.g. adding or removing files. Files can be from the filesystem or created on the fly, e.g. a picture taken from a camera connected to the user's device.

Constraint validation: If the element is required and the list of selected files is empty, then the element is suffering from being missing.

Unless the multiple attribute is set, there must be no more than one file in the list of selected files.


The accept attribute may be specified to provide user agents with a hint of what file types the server will be able to accept.

If specified, the attribute must consist of a set of comma-separated tokens, each of which must be an ASCII case-insensitive match for one of the following:

The string audio/*
Indicates that sound files are accepted.
The string video/*
Indicates that video files are accepted.
The string image/*
Indicates that image files are accepted.
A valid MIME type, with no parameters
Indicates that files of the specified type are accepted. [RFC2046]

The tokens must not be ASCII case-insensitive matches for any of the other tokens (i.e. duplicates are not allowed). To obtain the list of tokens from the attribute, the user agent must split the attribute value on commas.

User agents should prevent the user from selecting files that are not accepted by one (or more) of these tokens.


The following common input element content attributes apply to the element: accept, multiple, and required.

The value DOM attribute is in mode filename.

The change event applies.

The following content attributes must not be specified and do not apply to the element: alt, autocomplete, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, maxlength, min, pattern, placeholder, readonly, size, src, step, and width.

The element's value attribute must be omitted.

The following DOM attributes and methods do not apply to the element: checked, list, selectedOption, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

The input event does not apply.

4.10.4.1.18 Submit Button state

When an input element's type attribute is in the Submit Button state, the rules in this section apply.

The input element represents a button that, when activated, submits the form. If the element has a value attribute, the button's label must be the value of that attribute; otherwise, it must be an implementation-defined string that means "Submit" or some such. The element is a button, specifically a submit button.

If the element is mutable, the user agent should allow the user to activate the element.

The element's activation behavior, if the element has a form owner, is to submit the form owner from the input element; otherwise, it is to do nothing.

The formaction, formenctype, formmethod, formnovalidate, and formtarget attributes are attributes for form submission.

The following common input element content attributes and DOM attributes apply to the element: formaction, formenctype, formmethod, formnovalidate, and formtarget content attributes; value DOM attribute.

The value DOM attribute is in mode default.

The following content attributes must not be specified and do not apply to the element: accept, alt, autocomplete, checked, height, list, max, maxlength, min, multiple, pattern, placeholder, readonly, required size, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, list, selectedOption, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

The input and change events do not apply.

4.10.4.1.19 Image Button state

When an input element's type attribute is in the Image Button state, the rules in this section apply.

The input element represents either an image from which a user can select a coordinate and submit the form, or alternatively a button from which the user can submit the form. The element is a button, specifically a submit button.


The image is given by the src attribute. The src attribute must be present, and must contain a valid URL referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted.

When any of the following events occur, unless the user agent cannot support images, or its support for images has been disabled, or the user agent only fetches elements on demand, the user agent must resolve the value of the src attribute, relative to the element, and if that is successful, must fetch the resulting absolute URL:

Fetching the image must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined below) has been run.

If the image was successfully obtained, with no network errors, and the image's type is a supported image type, and the image is a valid image of that type, then the image is said to be available. If this is true before the image is completely downloaded, each task that is queued by the networking task source while the image is being fetched must update the presentation of the image appropriately.

The user agents should apply the image sniffing rules to determine the type of the image, with the image's associated Content-Type headers giving the official type. If these rules are not applied, then the type of the image must be the type given by the image's associated Content-Type headers.

User agents must not support non-image resources with the input element. User agents must not run executable code embedded in the image resource. User agents must only display the first page of a multipage resource. User agents must not allow the resource to act in an interactive fashion, but should honor any animation in the resource.

The task that is queued by the networking task source once the resource has been fetched, must, if the download was successful and the image is available, queue a task to fire a simple event called load at the input element; and otherwise, if the fetching process fails without a response from the remote server, or completes but the image is not a valid or supported image, queue a task to fire a simple event called error on the input element.


The alt attribute provides the textual label for the alternative button for users and user agents who cannot use the image. The alt attribute must also be present, and must contain a non-empty string.

The input element supports dimension attributes.


If the src attribute is set, and the image is available and the user agent is configured to display that image, then: The element represents a control for selecting a coordinate from the image specified by the src attribute; if the element is mutable, the user agent should allow the user to select this coordinate. The activation behavior in this case consists of taking the user's selected coordinate, and then, if the element has a form owner, submitting the input element's form owner from the input element. If the user activates the control without explicitly selecting a coordinate, then the coordinate (0,0) must be assumed.

Otherwise, the element represents a submit button whose label is given by the value of the alt attribute; if the element is mutable, the user agent should allow the user to activate the button. The activation behavior in this case consists of setting the selected coordinate to (0,0), and then, if the element has a form owner, submitting the input element's form owner from the input element.

The selected coordinate must consist of an x-component and a y-component. The x-component must be greater than or equal to zero, and less than or equal to the rendered width, in CSS pixels, of the image, plus the widths of the left and right borders rendered around the image, if any. The y-component must be greater than or equal to zero, and less than or equal to the rendered height, in CSS pixels, of the image, plus the widths of the top and bottom bordered rendered around the image, if any. The coordinates must be relative to the image's borders, where there are any, and the edge of the image otherwise.


The formaction, formenctype, formmethod, formnovalidate, and formtarget attributes are attributes for form submission.

The following common input element content attributes and DOM attributes apply to the element: alt, formaction, formenctype, formmethod, formnovalidate, formtarget, height, src, and width content attributes; value DOM attribute.

The value DOM attribute is in mode default.

The following content attributes must not be specified and do not apply to the element: accept, autocomplete, checked, list, max, maxlength, min, multiple, pattern, placeholder, readonly, required size, and step.

The element's value attribute must be omitted.

The following DOM attributes and methods do not apply to the element: checked, list, selectedOption, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

The input and change events do not apply.

Many aspects of this state's behavior are similar to the behavior of the img element. Readers are encouraged to read that section, where many of the same requirements are described in more detail.

4.10.4.1.20 Reset Button state

When an input element's type attribute is in the Reset Button state, the rules in this section apply.

The input element represents a button that, when activated, resets the form. If the element has a value attribute, the button's label must be the value of that attribute; otherwise, it must be an implementation-defined string that means "Reset" or some such. The element is a button.

If the element is mutable, the user agent should allow the user to activate the element.

The element's activation behavior, if the element has a form owner, is to reset the form owner; otherwise, it is to do nothing.

Constraint validation: The element is barred from constraint validation.

The value DOM attribute applies to this element and is in mode default.

The following content attributes must not be specified and do not apply to the element: accept, alt, autocomplete, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, maxlength, min, multiple, pattern, placeholder, readonly, required size, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, list, selectedOption, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

The input and change events do not apply.

4.10.4.1.21 Button state

When an input element's type attribute is in the Button state, the rules in this section apply.

The input element represents a button with no default behavior. If the element has a value attribute, the button's label must be the value of that attribute; otherwise, it must be the empty string. The element is a button.

If the element is mutable, the user agent should allow the user to activate the element. The element's activation behavior is to do nothing.

Constraint validation: The element is barred from constraint validation.

The value DOM attribute applies to this element and is in mode default.

The following content attributes must not be specified and do not apply to the element: accept, alt, autocomplete, checked, formaction, formenctype, formmethod, formnovalidate, formtarget, height, list, max, maxlength, min, multiple, pattern, placeholder, readonly, required size, src, step, and width.

The following DOM attributes and methods do not apply to the element: checked, list, selectedOption, selectionStart, selectionEnd, valueAsDate, and valueAsNumber DOM attributes; select(), setSelectionRange(), stepDown(), and stepUp() methods.

The input and change events do not apply.

4.10.4.2 Common input element attributes

These attributes only apply to an input element if its type attribute is in a state whose definition declares that the attribute applies. When an attribute doesn't apply to an input element, user agents must ignore the attribute.

4.10.4.2.1 The autocomplete attribute

The autocomplete attribute is an enumerated attribute. The attribute has three states. The on keyword maps to the on state, and the off keyword maps to the off state. The attribute may also be omitted. The missing value default is the default state.

The off state indicates that the control's input data is either particularly sensitive (for example the activation code for a nuclear weapon) or is a value that will never be reused (for example a one-time-key for a bank login) and the user will therefore have to explicitly enter the data each time, instead of being able to rely on the UA to prefill the value for him.

Conversely, the on state indicates that the value is not particularly sensitive and the user can expect to be able to rely on his user agent to remember values he has entered for that control.

The default state indicates that the user agent is to use the autocomplete attribute on the element's form owner instead.

Each input element has a resulting autocompletion state, which is either on or off.

When an input element's autocomplete attribute is in the on state, when an input element's autocomplete attribute is in the default state, and the element has no form owner, and when an input element's autocomplete attribute is in the default state, and the element's form owner's autocomplete attribute is in the on state, the input element's resulting autocompletion state is on. Otherwise, the input element's resulting autocompletion state is off.

When an input element's resulting autocompletion state is on, the user agent may store the value entered by the user so that if the user returns to the page, the UA can prefill the form. Otherwise, the user agent should not remember the control's value.

The autocompletion mechanism must be implemented by the user agent acting as if the user had modified the element's value, and must be done at a time where the element is mutable (e.g. just after the element has been inserted into the document, or when the user agent stops parsing).

Banks frequently do not want UAs to prefill login information:

<p>Account: <input type="text" name="ac" autocomplete="off"></p>
<p>PIN: <input type="text" name="pin" autocomplete="off"></p>

A user agent may allow the user to override the resulting autocompletion state and set it to always on, always allowing values to be remembered and prefilled), or always off, never remembering values. However, the ability to override the resulting autocompletion state to on should not be trivially accessible, as there are significant security implications for the user if all values are always remembered, regardless of the site's preferences.

4.10.4.2.2 The list attribute

The list attribute is used to identify an element that lists predefined options suggested to the user.

If present, its value must be the ID of a datalist element in the same document.

The suggestions source element is the first element in the document in tree order to have an ID equal to the value of the list attribute, if that element is a datalist element. If there is no list attribute, or if there is no element with that ID, or if the first element with that ID is not a datalist element, then there is no suggestions source element.

If there is a suggestions source element, then, when the user agent is allowing the user to edit the input element's value, the user agent should offer the suggestions represented by the suggestions source element to the user in a manner suitable for the type of control used. The user agent may use the suggestion's label to identify the suggestion if appropriate. If the user selects a suggestion, then the input element's value must be set to the selected suggestion's value, as if the user had written that value himself.

User agents must filter the suggestions to hide suggestions that the user would not be allowed to enter as the input element's value, and should filter the suggestions to hide suggestions that would cause the element to not satisfy its constraints.


If the list attribute does not apply, there is no suggestions source element.

4.10.4.2.3 The readonly attribute

The readonly attribute is a boolean attribute that controls whether or not the use can edit the form control. When specified, the element is immutable.

Constraint validation: If the readonly attribute is specified on an input element, the element is barred from constraint validation.

4.10.4.2.4 The size attribute

The size attribute gives the number of characters that, in a visual rendering, the user agent is to allow the user to see while editing the element's value.

The size attribute, if specified, must have a value that is a valid non-negative integer greater than zero.

If the attribute is present, then its value must be parsed using the rules for parsing non-negative integers, and if the result is a number greater than zero, then the user agent should ensure that at least that many characters are visible.

The size DOM attribute limited to only positive non-zero numbers.

4.10.4.2.5 The required attribute

The required attribute is a boolean attribute. When specified, the element is required.

Constraint validation: If the element is required, and its value DOM attribute applies and is in the mode value, and the element is mutable, and the element's value is the empty string, then the element is suffering from being missing.

4.10.4.2.6 The multiple attribute

The multiple attribute is a boolean attribute that indicates whether the user is to be allowed to specify more than one value.

4.10.4.2.7 The maxlength attribute

The maxlength attribute, when it applies, is a form control maxlength attribute controlled by the input element's dirty value flag.

If the input element has a maximum allowed value length, then the code-point length of the value of the element's value attribute must be equal to or less than the element's maximum allowed value length.

4.10.4.2.8 The pattern attribute

The pattern attribute specifies a regular expression against which the control's value is to be checked.

If specified, the attribute's value must match the JavaScript Pattern production. [ECMA262]

Constraint validation: If the element's value is not the empty string, and the element's pattern attribute is specified and the attribute's value, when compiled as a JavaScript regular expression with the global, ignoreCase, and multiline flags disabled (see ECMA262 Edition 3, sections 15.10.7.2 through 15.10.7.4), compiles successfully but the resulting regular expression does not match the entirety of the element's value, then the element is suffering from a pattern mismatch. [ECMA262]

This implies that the regular expression language used for this attribute is the same as that used in JavaScript, except that the pattern attribute must match the entire value, not just any subset (somewhat as if it implied a ^(?: at the start of the pattern and a )$ at the end).

When an input element has a pattern attribute specified, authors should include a title attribute to give a description of the pattern. User agents may use the contents of this attribute, if it is present, when informing the user that the pattern is not matched, or at any other suitable time, such as in a tooltip or read out by assistive technology when the control gains focus.

For example, the following snippet:

<label> Part number:
 <input pattern="[0-9][A-Z]{3}" name="part"
        title="A part number is a digit followed by three uppercase letters."/>
</label>

...could cause the UA to display an alert such as:

 part number is a digit followed by three uppercase letters.
You cannot complete this form until the field is correct.

When a control has a pattern attribute, the title attribute, if used, must describe the pattern. Additional information could also be included, so long as it assists the user in filling in the control. Otherwise, assistive technology would be impaired.

For instance, if the title attribute contained the caption of the control, assistive technology could end up saying something like The text you have entered does not match the required pattern. Birthday, which is not useful.

UAs may still show the title in non-error situations (for example, as a tooltip when hovering over the control), so authors should be careful not to word titles as if an error has necessarily occurred.

4.10.4.2.9 The min and max attributes

The min and max attributes indicate the allowed range of values for the element.

Their syntax is defined by the section that defines the type attribute's current state.

If the element has a min attribute, and the result of applying the algorithm to convert a string to a number to the value of the min attribute is a number, then that number is the element's minimum; otherwise, if the type attribute's current state defines a default minimum, then that is the minimum; otherwise, the element has no minimum.)

Constraint validation: When the element has a minimum, and the result of applying the algorithm to convert a string to a number to the string given by the element's value is a number, and the number obtained from that algorithm is less than the minimum, the element is suffering from an underflow.

The min attribute also defines the step base.

If the element has a max attribute, and the result of applying the algorithm to convert a string to a number to the value of the max attribute is a number, then that number is the element's maximum; otherwise, if the type attribute's current state defines a default maximum, then that is the maximum; otherwise, the element has no maximum.)

Constraint validation: When the element has a maximum, and the result of applying the algorithm to convert a string to a number to the string given by the element's value is a number, and the number obtained from that algorithm is more than the maximum, the element is suffering from an overflow.

The max attribute's value (the maximum) must not be less than the min attribute's value (its minimum).

If an element has a maximum that is less than its minimum, then so long as the element has a value, it will either be suffering from an underflow or suffering from an overflow.

4.10.4.2.10 The step attribute

The step attribute indicates the granularity that is expected (and required) of the value, by limiting the allowed values. The section that defines the type attribute's current state also defines the default step and the step scale factor, which are used in processing the attribute as described below.

The step attribute, if specified, must either have a value that is a valid floating point number that parses to a number that is greater than zero, or must have a value that is an ASCII case-insensitive match for the string "any".

The attribute provides the allowed value step for the element, as follows:

  1. If the attribute is absent, then the allowed value step is the default step multiplied by the step scale factor.
  2. Otherwise, if the attribute's value is an ASCII case-insensitive match for the string "any", then there is no allowed value step.
  3. Otherwise, if the rules for parsing floating point number values, when they are applied to the attribute's value, return an error, zero, or a number less than zero, then the allowed value step is the default step multiplied by the step scale factor.
  4. Otherwise, the allowed value step is the number returned by the rules for parsing floating point number values when they are applied to the attribute's value, multiplied by the step scale factor.

The step base is the result of applying the algorithm to convert a string to a number to the value of the min attribute, unless the element does not have a min attribute specified or the result of applying that algorithm is an error, in which case the step base is zero.

Constraint validation: When the element has an allowed value step, and the result of applying the algorithm to convert a string to a number to the string given by the element's value is a number, and that number subtracted from the step base is not an integral multiple of the allowed value step, the element is suffering from a step mismatch.

4.10.4.2.11 The placeholder attribute

The placeholder attribute represents a short hint (a word or short phrase) intended to aid the user with data entry. A hint could be a sample value or a brief description of the expected format. The attribute, if specified, must have a value that contains no U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters.

For a longer hint or other advisory text, the title attribute is more appropriate.

The placeholder attribute should not be used as an alternative to a label.

User agents should present this hint to the user, after having stripped line breaks from it, when the element's value is the empty string and the control is not focused (e.g. by displaying it inside a blank unfocused control).

Here is an example of a mail configuration user interface that uses the placeholder attribute:

<fieldset>
 <legend>Mail Account</legend>
 <p><label>Name: <input type="text" name="fullname" placeholder="John Ratzenberger"></label></p>
 <p><label>Address: <input type="email" name="address" placeholder="john@example.net"></label></p>
 <p><label>Password: <input type="password" name="password"></label></p>
 <p><label>Description: <input type="text" name="desc" placeholder="My Email Account"></label></p>
</fieldset>
4.10.4.3 Common input element APIs
input . value [ = value ]

Returns the current value of the form control.

Can be set, to change the value.

Throws an INVALID_ACCESS_ERR exception if it is set when the control is a file upload control.

input . checked [ = value ]

Returns the current checkedness of the form control.

Can be set, to change the checkedness.

input . valueAsDate [ = value ]

Returns a Date object representing the form control's value, if applicable; otherwise, returns null.

Can be set, to change the value.

Throws an INVALID_ACCESS_ERR exception if the control isn't date- or time-based.

input . valueAsNumber [ = value ]

Returns a number representing the form control's value, if applicable; otherwise, returns null.

Can be set, to change the value.

Throws an INVALID_ACCESS_ERR exception if the control is neither date- or time-based nor numeric.

input . stepUp()
input . stepDown()

Changes the form control's value by the value given in the step attribute.

Throws INVALID_ACCESS_ERR exception if the control is neither date- or time-based nor numeric, if the step attribute's value is "any", if the current value could not be parsed, or if stepping in the given direction would take the value out of range.

input . list

Returns the datalist element indicated by the list attribute.

input . selectedOption

Returns the option element from the datalist element indicated by the list attribute that matches the form control's value.

The value DOM attribute allows scripts to manipulate the value of an input element. The attribute is in one of the following modes, which define its behavior:

value
On getting, it must return the current value of the element. On setting, it must set the element's value to the new value, set the element's dirty value flag to true, and then invoke the value sanitization algorithm, if the element's type attribute's current state defines one.
default
On getting, if the element has a value attribute, it must return that attribute's value; otherwise, it must return the empty string. On setting, it must set the element's value attribute to the new value.
default/on
On getting, if the element has a value attribute, it must return that attribute's value; otherwise, it must return the string "on". On setting, it must set the element's value attribute to the new value.
filename
On getting, it must return the string "C:\fakepath\" followed by the filename of the first file in the list of selected files, if any, or the empty string if the list is empty. On setting, it must throw an INVALID_ACCESS_ERR exception.

The checked DOM attribute allows scripts to manipulate the checkedness of an input element. On getting, it must return the current checkedness of the element; and on setting, it must set the element's checkedness to the new value and set the element's dirty checkedness flag to true.


The valueAsDate DOM attribute represents the value of the element, interpreted as a date.

On getting, if the valueAsDate attribute does not apply, as defined for the input element's type attribute's current state, then return null. Otherwise, run the algorithm to convert a string to a Date object defined for that state; if the algorithm returned a Date object, then return it, otherwise, return null.

On setting, if the valueAsDate attribute does not apply, as defined for the input element's type attribute's current state, then throw an INVALID_ACCESS_ERR exception; otherwise, if the new value is null, then set the value of the element to the empty string; otherwise, run the algorithm to convert a Date object to a string, as defined for that state, on the new value, and set the value of the element to resulting string.


The valueAsNumber DOM attribute represents the value of the element, interpreted as a number.

On getting, if the valueAsNumber attribute does not apply, as defined for the input element's type attribute's current state, then return a Not-a-Number (NaN) value. Otherwise, if the valueAsDate attribute applies, run the algorithm to convert a string to a Date object defined for that state; if the algorithm returned a Date object, then return the time value of the object (the number of milliseconds from midnight UTC the morning of 1970-01-01 to the time represented by the Date object), otherwise, return a Not-a-Number (NaN) value. Otherwise, run the algorithm to convert a string to a number defined for that state; if the algorithm returned a number, then return it, otherwise, return a Not-a-Number (NaN) value.

On setting, if the valueAsNumber attribute does not apply, as defined for the input element's type attribute's current state, then throw an INVALID_ACCESS_ERR exception. Otherwise, if the valueAsDate attribute applies, run the algorithm to convert a Date object to a string defined for that state, passing it a Date object whose time value is the new value, and set the value of the element to resulting string. Otherwise, run the algorithm to convert a number to a string, as defined for that state, on the new value, and set the value of the element to resulting string.


The stepDown() and stepUp() methods, when invoked, must run the following algorithm:

  1. If the stepDown() and stepUp() methods do not apply, as defined for the input element's type attribute's current state, then throw an INVALID_ACCESS_ERR exception, and abort these steps.

  2. If the element has no allowed value step, then throw an INVALID_ACCESS_ERR exception, and abort these steps.

  3. If applying the algorithm to convert a string to a number to the string given by the element's value results in an error, then throw an INVALID_ACCESS_ERR exception, and abort these steps; otherwise, let value be the result of that algorithm.

  4. Let delta be the allowed value step.

  5. If the method invoked was the stepDown() method, negate delta.

  6. Let value be the result of adding delta to value.

  7. If the element has a minimum, and the value is less than that minimum, then throw a INVALID_ACCESS_ERR exception.

  8. If the element has a maximum, and the value is greater than that maximum, then throw a INVALID_ACCESS_ERR exception.

  9. Let value as string be the result of running the algorithm to convert a number to a string, as defined for the input element's type attribute's current state, on value.

  10. Set the value of the element to value as string.


The list DOM attribute must return the current suggestions source element, if any, or null otherwise.

The selectedOption DOM attribute must return the first option element, in tree order, to be a child of the suggestions source element and whose value matches the input element's value, if any. If there is no suggestions source element, or if it contains no matching option element, then the selectedOption attribute must return null.

4.10.4.4 Common event behaviors

When the input event applies, any time the user causes the element's value to change, the user agent must queue a task to fire a simple event called input at the input element, then broadcast forminput events at the input element's form owner. User agents may wait for a suitable break in the user's interaction before queuing the task; for example, a user agent could wait for the user to have not hit a key for 100ms, so as to only fire the event when the user pauses, instead of continuously for each keystroke.

Examples of a user changing the element's value would include the user typing into a text field, pasting a new value into the field, or undoing an edit in that field. Some user interactions do not cause changes to the value, e.g. hitting the "delete" key in an empty text field, or replacing some text in the field with text from the clipboard that happens to be exactly the same text.

When the change event applies, if the element does not have an activation behavior defined but uses a user interface that involves an explicit commit action, then any time the user commits a change to the element's value or list of selected files, the user agent must queue a task to fire a simple event called change at the input element, then broadcast formchange events at the input element's form owner.

An example of a user interface with a commit action would be a File Upload control that consists of a single button that brings up a file selection dialog: when the dialog is closed, if that the file selection changed as a result, then the user has committed a new file selection.

Another example of a user interface with a commit action would be a Date control that allows both text-based user input and user selection from a drop-down calendar: while text input might not have an explicit commit step, selecting a date from the drop down calendar and then dismissing the drop down would be a commit action.

When the user agent changes the element's value on behalf of the user (e.g. as part of a form prefilling feature), the user agent must follow these steps:

  1. If the input event applies, queue a task to fire a simple event called input at the input element.
  2. If the input event applies, broadcast forminput events at the input element's form owner.
  3. If the change event applies, queue a task to fire a simple event called change at the input element.
  4. If the change event applies, broadcast formchange events at the input element's form owner.

In addition, when the change event applies, change events can also be fired as part of the element's activation behavior and as part of the unfocusing steps.

The task source for these task is the user interaction task source.

4.10.5 The button element

Categories
Flow content.
Phrasing content.
Interactive content.
Listed, labelable, and submittable form-associated element.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content, but there must be no interactive content descendant.
Content attributes:
Global attributes
autofocus
disabled
form
formaction
formenctype
formmethod
formnovalidate
formtarget
name
type
value
DOM interface:
interface HTMLButtonElement : HTMLElement {
           attribute boolean autofocus;
           attribute boolean disabled;
  readonly attribute HTMLFormElement form;
           attribute DOMString formaction;
           attribute DOMString formenctype;
           attribute DOMString formmethod;
           attribute DOMString formnoValidate;
           attribute DOMString formtarget;
           attribute DOMString name;
           attribute DOMString type;
           attribute DOMString value;

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);

  readonly attribute NodeList labels;
};

The button element represents a button. If the element is not disabled, then the user agent should allow the user to activate the button.

The element is a button.

The type attribute controls the behavior of the button when it is activated. It is an enumerated attribute. The following table lists the keywords and states for the attribute — the keywords in the left column map to the states in the cell in the second column on the same row as the keyword.

Keyword State Brief description
submit Submit Button Submits the form.
reset Reset Button Resets the form.
button Button Does nothing.

The missing value default is the Submit Button state.

If the type attribute is in the Submit Button state, the element is specifically a submit button.

If the element is not disabled, the activation behavior of the button element is to run the steps defined in the following list for the current state of the element's type attribute.

Submit Button

If the element has a form owner, the element must submit the form owner from the button element.

Reset Button

If the element has a form owner, the element must reset the form owner.

Button

Do nothing.

The form attribute is used to explicitly associate the button element with its form owner. The name attribute represents the element's name. The disabled attribute is used to make the control non-interactive and to prevent its value from being submitted. The autofocus attribute controls focus. The formaction, formenctype, formmethod, formnovalidate, and formtarget attributes are attributes for form submission.

The value attribute gives the element's value for the purposes of form submission. The value attribute must not be present unless the form attribute is present. The element's value is the value of the element's value attribute, if there is one, or the empty string otherwise.

A button (and its value) is only included in the form submission if the button itself was used to initiate the form submission.

The value and type DOM attributes must reflect the respective content attributes of the same name.

The willValidate, validity, and validationMessage attributes, and the checkValidity() and setCustomValidity() methods, are part of the constraint validation API. The labels attribute provides a list of the element's labels.

4.10.6 The select element

Categories
Flow content.
Phrasing content.
Interactive content.
Listed, labelable, submittable, and resettable form-associated element.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Zero or more option or optgroup elements.
Content attributes:
Global attributes
autofocus
disabled
form
multiple
name
size
DOM interface:
[Callable=namedItem]
interface HTMLSelectElement : HTMLElement {
           attribute boolean autofocus;
           attribute boolean disabled;
  readonly attribute HTMLFormElement form;
           attribute boolean multiple;
           attribute DOMString name;
           attribute boolean size;

  readonly attribute DOMString type;

  readonly attribute HTMLOptionsCollection options;
           attribute unsigned long length;
  [IndexGetter] any item(in DOMString name);
  [NameGetter] any namedItem(in DOMString name);
  void add(in HTMLElement element, [Optional] in HTMLElement before);
  void add(in HTMLElement element, in long before);
  void remove(in long index);

  readonly attribute HTMLCollection selectedOptions;
           attribute long selectedIndex;
           attribute DOMString value;

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);

  readonly attribute NodeList labels;
};

The select element represents a control for selecting amongst a set of options.

The multiple attribute is a boolean attribute. If the attribute is present, then the select element represents a control for selecting zero or more options from the list of options. If the attribute is absent, then the select element represents a control for selecting a single option from the list of options.

The list of options for a select element consists of all the option element children of the select element, and all the option element children of all the optgroup element children of the select element, in tree order.

The size attribute gives the number of options to show to the user. The size attribute, if specified, must have a value that is a valid non-negative integer greater than zero. If the multiple attribute is present, then the size attribute's default value is 4. If the multiple attribute is absent, then the size attribute's default value is 1.

If the multiple attribute is absent, and the element is not disabled, then the user agent should allow the user to pick an option element in its list of options that is itself not disabled. Upon this option element being picked (either through a click, or through unfocusing the element after changing its value, or through a menu command, or through any other mechanism), and before the relevant user interaction event is queued (e.g. before the click event), the user agent must set the selectedness of the picked option element to true and then queue a task to fire a simple event called change at the select element, using the user interaction task source as the task source, then broadcast formchange events at the element's form owner.

If the multiple attribute is absent, whenever an option element in the select element's list of options has its selectedness set to true, and whenever an option element with its selectedness set to true is added to the select element's list of options, the user agent must set the selectedness of all the other option element in its list of options to false.

If the multiple attribute is absent, whenever there are no option elements in the select element's list of options that have their selectedness set to true, the user agent must set the selectedness of the first option element in the list of options in tree order that is not disabled, if any, to true.

If the multiple attribute is present, and the element is not disabled, then the user agent should allow the user to toggle the selectedness of the option elements in its list of options that are themselves not disabled (either through a click, or through a menu command, or any other mechanism). Upon the selectedness of one or more option elements being changed by the user, and before the relevant user interaction event is queued (e.g. before a related click event), the user agent must queue a task to fire a simple event called change at the select element, using the user interaction task source as the task source, then broadcast formchange events at the element's form owner.

The reset algorithm for select elements is to go through all the option elements in the element's list of options, and set their selectedness to true if the option element has a selected attribute, and false otherwise.

The form attribute is used to explicitly associate the select element with its form owner. The name attribute represents the element's name. The disabled attribute is used to make the control non-interactive and to prevent its value from being submitted. The autofocus attribute controls focus.

select . type

Returns "select-multiple" if the element has a multiple attribute, and "select-one" otherwise.

select . options

Returns an HTMLOptionsCollection of the list of options.

select . length [ = value ]

Returns the number of elements in the list of options.

When set to a smaller number, truncates the number of option elements in the select.

When set to a greater number, adds new blank option elements to the select.

element = select . item(index)
select[index]

Returns the item with index index from the list of options. The items are sorted in tree order.

Returns null if index is out of range.

element = select . namedItem(name)
select[name]

Returns the item with ID or name name from the list of options.

If there are multiple matching items, then a NodeList object containing all those elements is returned.

Returns null if no element with that ID could be found.

select . add(element [, before ])

Inserts element before the node given by before.

The before argument can be a number, in which case element is inserted before the item with that number, or an element from the list of options, in which case element is inserted before that element.

If before is omitted, null, or a number out of range, then element will be added at the end of the list.

This method will throw a HIERARCHY_REQUEST_ERR exception if element is an ancestor of the element into which it is to be inserted. If element is not an option or optgroup element, then the method does nothing.

select . selectedOptions

Returns an HTMLCollection of the list of options that are selected.

select . selectedIndex [ = value ]

Returns the index of the first selected item, if any, or −1 if there is no selected item.

Can be set, to change the selection.

select . value [ = value ]

Returns the value of the first selected item, if any, or the empty string if there is no selected item.

Can be set, to change the selection.

The type DOM attribute, on getting, must return the string "select-one" if the multiple attribute is absent, and the string "select-multiple" if the multiple attribute is present.

The options DOM attribute must return an HTMLOptionsCollection rooted at the select node, whose filter matches the elements in the list of options.

The options collection is also mirrored on the HTMLSelectElement object. The indices of the supported indexed properties at any instant are the indices supported by the object returned by the options attribute at that instant. The names of the supported named properties at any instant are the names supported by the object returned by the options attribute at that instant.

The length DOM attribute must return the number of nodes represented by the options collection. On setting, it must act like the attribute of the same name on the options collection.

The item(index) method must return the value returned by the method of the same name on the options collection, when invoked with the same argument.

The namedItem(name) method must return the value returned by the method of the same name on the options collection, when invoked with the same argument.

Similarly, the add() and remove() methods must act like their namesake methods on that same options collection.

The selectedOptions DOM attribute must return an HTMLCollection rooted at the select node, whose filter matches the elements in the list of options that have their selectedness set to true.

The selectedIndex DOM attribute, on getting, must return the index of the first option element in the list of options in tree order that has its selectedness set to true, if any. If there isn't one, then it must return −1.

On setting, the selectedIndex attribute must set the selectedness of all the option elements in the list of options to false, and then the option element in the list of options whose index is the given new value, if any, must have its selectedness set to true.

The value DOM attribute, on getting, must return the value of the first option element in the list of options in tree order that has its selectedness set to true, if any. If there isn't one, then it must return the empty string.

On setting, the value attribute must set the selectedness of all the option elements in the list of options to false, and then first the option element in the list of options, in tree order, whose value is equal to the given new value, if any, must have its selectedness set to true.

The multiple and size DOM attributes must reflect the respective content attributes of the same name. The size DOM attribute limited to only positive non-zero numbers.

The willValidate, validity, and validationMessage attributes, and the checkValidity() and setCustomValidity() methods, are part of the constraint validation API. The labels attribute provides a list of the element's labels.

4.10.7 The datalist element

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Either: phrasing content.
Or: Zero or more option elements.
Content attributes:
Global attributes
DOM interface:
interface HTMLDataListElement : HTMLElement {
  readonly attribute HTMLCollection options;
};

The datalist element represents a set of option elements that represent predefined options for other controls. The contents of the element represents fallback content for legacy user agents, intermixed with option elements that represent the predefined options. In the rendering, the datalist element represents nothing and it, along with its children, should be hidden.

The datalist element is hooked up to an input element using the list attribute on the input element. The datalist element can also be used with a datagrid element, as the source of autocompletion hints for editable cells.

Each option element that is a descendant of the datalist element, that is not disabled, and whose value is a string that isn't the empty string, represents a suggestion. Each suggestion has a value and a label.

datalist . options

Returns an HTMLCollection of the options elements of the table.

The options DOM attribute must return an HTMLCollection rooted at the datalist node, whose filter matches option elements.

Constraint validation: If an element has a datalist element ancestor, it is barred from constraint validation.

4.10.8 The optgroup element

Categories
None.
Contexts in which this element may be used:
As a child of a select element.
Content model:
Zero or more option elements.
Content attributes:
Global attributes
disabled
label
DOM interface:
interface HTMLOptGroupElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString label;
};

The optgroup element represents a group of option elements with a common label.

The element's group of option elements consists of the option elements that are children of the optgroup element.

When showing option elements in select elements, user agents should show the option elements of such groups as being related to each other and separate from other option elements.

The disabled attribute is a boolean attribute and can be used to disable a group of option elements together.

The label attribute must be specified. Its value gives the name of the group, for the purposes of the user interface. User agents should use this attribute's value when labelling the group of option elements in a select element.

The disabled and label attributes must reflect the respective content attributes of the same name.

4.10.9 The option element

Categories
None.
Contexts in which this element may be used:
As a child of a select element.
As a child of a datalist element.
As a child of an optgroup element.
Content model:
Text.
Content attributes:
Global attributes
disabled
label
selected
value
DOM interface:
[NamedConstructor=Option(),
 NamedConstructor=Option(in DOMString text),
 NamedConstructor=Option(in DOMString text, in DOMString value),
 NamedConstructor=Option(in DOMString text, in DOMString value, in boolean defaultSelected),
 NamedConstructor=Option(in DOMString text, in DOMString value, in boolean defaultSelected, in boolean selected)]
interface HTMLOptionElement : HTMLElement {
           attribute boolean disabled;
  readonly attribute HTMLFormElement form;
           attribute DOMString label;
           attribute boolean defaultSelected;
           attribute boolean selected;
           attribute DOMString value;

  readonly attribute DOMString text;
  readonly attribute long index;
};

The option element represents an option in a select element or as part of a list of suggestions in a datalist element.

The disabled attribute is a boolean attribute. An option element is disabled if its disabled attribute is present or if it is a child of an optgroup element whose disabled attribute is present.

An option element that is disabled must prevent any click events that are queued on the user interaction task source from being dispatched on the element.

The label attribute provides a label for element. The label of an option element is the value of the label attribute, if there is one, or the textContent of the element, if there isn't.

The value attribute provides a value for element. The value of an option element is the value of the value attribute, if there is one, or the textContent of the element, if there isn't.

The selected attribute represents the default selectedness of the element.

The selectedness of an option element is a boolean state, initially false. If the element is disabled, then the element's selectedness is always false and cannot be set to true. Unless otherwise specified, when the element is created, its selectedness must be set to true if the element has a selected attribute. Whenever an option element's selected attribute is added, its selectedness must be set to true.

The Option() constructor with two or more arguments overrides the initial state of the selectedness state to always be false even if the third argument is true (implying that a selected attribute is to be set).

An option element's index is the number of option element that are in the same list of options but that come before it in tree order. If the option element is not in a list of options, then the option element's index is zero.

option . selected

Returns true if the element is selected, and false otherwise.

option . index

Returns the index of the element in its select element's options list.

option . form

Returns the element's form element, if any, or null otherwise.

option = new Option( [ text [, value [, defaultSelected [, selected ] ] ] ] )

Returns a new option element.

The text argument sets the contents of the element.

The value argument sets the value attribute.

The defaultSelected argument sets the selected attribute.

The selected argument sets whether or not the element is selected. If it is omitted, even if the defaultSelected argument is true, the element is not selected.

The disabled, label, and value DOM attributes must reflect the respective content attributes of the same name. The defaultSelected DOM attribute must reflect the selected content attribute.

The selected DOM attribute must return true if the element's selectedness is true, and false otherwise.

The index DOM attribute must return the element's index.

The text DOM attribute must return the same value as the textContent DOM attribute on the element.

The form DOM attribute's behavior depends on whether the option element is in a select element or not. If the option has a select element as its parent, or has a colgroup element as its parent and that colgroup element has a select element as its parent, then the form DOM attribute must return the same value as the form DOM attribute on that select element. Otherwise, it must return null.

Several constructors are provided for creating HTMLOptionElement objects (in addition to the factory methods from DOM Core such as createElement()): Option(), Option(text), Option(text, value), Option(text, value, defaultSelected), and Option(text, value, defaultSelected, selected). When invoked as constructors, these must return a new HTMLOptionElement object (a new option element). If the text argument is present, the new object must have as its only child a Node with node type TEXT_NODE (3) whose data is the value of that argument. If the value argument is present, the new object must have a value attribute set with the value of the argument as its value. If the defaultSelected argument is present and true, the new object must have a selected attribute set with no value. If the selected argument is present and true, the new object must have its selectedness set to true; otherwise the fourth argument is absent or false, and the selectedness must be set to false, even if the defaultSelected argument is present and true.

4.10.10 The textarea element

Categories
Flow content.
Phrasing content.
Interactive content.
Listed, labelable, submittable, and resettable form-associated element.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Text.
Content attributes:
Global attributes
autofocus
cols
disabled
form
maxlength
name
placeholder
readonly
required
rows
wrap
DOM interface:
interface HTMLTextAreaElement : HTMLElement {
           attribute boolean autofocus;
           attribute unsigned long cols;
           attribute boolean disabled;
  readonly attribute HTMLFormElement form;
           attribute long maxLength;
           attribute DOMString name;
           attribute DOMString placeholder;
           attribute boolean readOnly;
           attribute boolean required;
           attribute unsigned long rows;
           attribute DOMString wrap;

  readonly attribute DOMString type;
           attribute DOMString defaultValue;
           attribute DOMString value;

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);

  readonly attribute NodeList labels;

  void select();
           attribute unsigned long selectionStart;
           attribute unsigned long selectionEnd;
  void setSelectionRange(in unsigned long start, in unsigned long end);
};

The textarea element represents a multiline plain text edit control for the element's raw value. The contents of the control represent the control's default value.

The raw value of a textarea control must be initially the empty string.

The readonly attribute is a boolean attribute used to control whether the text can be edited by the user or not.

Constraint validation: If the readonly attribute is specified on a textarea element, the element is barred from constraint validation.

A textarea element is mutable if it is neither disabled nor has a readonly attribute specified.

When a textarea is mutable, its raw value should be editable by the user. Any time the user causes the element's raw value to change, the user agent must queue a task to fire a simple event called input at the textarea element, then broadcast forminput events at the textarea element's form owner. User agents may wait for a suitable break in the user's interaction before queuing the task; for example, a user agent could wait for the user to have not hit a key for 100ms, so as to only fire the event when the user pauses, instead of continuously for each keystroke.

A textarea element has a dirty value flag, which must be initially set to false, and must be set to true whenever the user interacts with the control in a way that changes the raw value.

When the textarea element's textContent DOM attribute changes value, if the element's dirty value flag is false, then the element's raw value must be set to the value of the element's textContent DOM attribute.

The reset algorithm for textarea elements is to set the element's value to the value of the element's textContent DOM attribute.

The cols attribute specifies the expected maximum number of characters per line. If the cols attribute is specified, its value must be a valid non-negative integer greater than zero. If applying the rules for parsing non-negative integers to the attribute's value results in a number greater than zero, then the element's character width is that value; otherwise, it is 20.

The user agent may use the textarea element's character width as a hint to the user as to how many characters the server prefers per line (e.g. for visual user agents by making the width of the control be that many characters). In visual renderings, the user agent should wrap the user's input in the rendering so that each line is no wider than this number of characters.

The rows attribute specifies the number of lines to show. If the rows attribute is specified, its value must be a valid non-negative integer greater than zero. If applying the rules for parsing non-negative integers to the attribute's value results in a number greater than zero, then the element's character height is that value; otherwise, it is 2.

Visual user agents should set the height of the control to the number of lines given by character height.

The wrap attribute is an enumerated attribute with two keywords and states: the soft keyword which maps to the Soft state, and the hard keyword which maps to the Hard state. The missing value default is the Soft state.

If the element's wrap attribute is in the Hard state, the cols attribute must be specified.

The element's value is defined to be the element's raw value with the following transformation applied:

  1. Replace every occurrence of a U+000D CARRIAGE RETURN (CR) character not followed by a U+000A LINE FEED (LF) character, and every occurrence of a U+000A LINE FEED (LF) character not proceeded by a U+000D CARRIAGE RETURN (CR) character, by a two-character string consisting of a U+000D CARRIAGE RETURN - U+000A LINE FEED (CRLF) character pair.

  2. If the element's wrap attribute is in the Hard state, insert U+000D CARRIAGE RETURN - U+000A LINE FEED (CRLF) character pairs into the string using a UA-defined algorithm so that each line so that each line has no more than character width characters. The purposes of this requirement, lines are delimited by the start of the string, the end of the string, and U+000D CARRIAGE RETURN - U+000A LINE FEED (CRLF) character pairs.

The maxlength attribute is a form control maxlength attribute controlled by the textarea element's dirty value flag.

If the textarea element has a maximum allowed value length, then the element's children must be such that the code-point length of the value of the element's textContent DOM attribute is equal to or less than the element's maximum allowed value length.

The required attribute is a boolean attribute. When specified, the user will be required to enter a value before submitting the form.

Constraint validation: If the element has its required attribute specified, and the element is mutable, and the element's value is the empty string, then the element is suffering from being missing.

The placeholder attribute represents a hint (a word or short phrase) intended to aid the user with data entry. A hint could be a sample value or a brief description of the expected format. The attribute, if specified, must have a value that contains no U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters.

For a longer hint or other advisory text, the title attribute is more appropriate.

The placeholder attribute should not be used as an alternative to a label.

User agents should present this hint to the user, after having stripped line breaks from it, when the element's value is the empty string and the control is not focused (e.g. by displaying it inside a blank unfocused control).

The form attribute is used to explicitly associate the textarea element with its form owner. The name attribute represents the element's name. The disabled attribute is used to make the control non-interactive and to prevent its value from being submitted. The autofocus attribute controls focus.

textarea . type

Returns the string "textarea".

textarea . value

Returns the current value of the element.

Can be set, to change the value.

The cols, placeholder, required, rows, and wrap attributes must reflect the respective content attributes of the same name. The cols and rows attributes are limited to only positive non-zero numbers. The maxLength DOM attribute must reflect the maxlength content attribute. The readOnly DOM attribute must reflect the readonly content attribute.

The type DOM attribute must return the value "textarea".

The defaultValue DOM attribute must act like the element's textContent DOM attribute.

The value attribute must, on getting, return the element's raw value; on setting, it must set the element's raw value to the new value.

The willValidate, validity, and validationMessage attributes, and the checkValidity() and setCustomValidity() methods, are part of the constraint validation API. The labels attribute provides a list of the element's labels. The select(), selectionStart, selectionEnd, and setSelectionRange() methods and attributes expose the element's text selection.

4.10.11 The keygen element

Categories
Flow content.
Phrasing content.
Interactive content.
Listed, labelable, submittable, and resettable form-associated element.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Empty.
Content attributes:
Global attributes
autofocus
challenge
disabled
form
keytype
name
DOM interface:
interface HTMLKeygenElement : HTMLElement {
           attribute boolean autofocus;
           attribute DOMString challenge;
           attribute boolean disabled;
  readonly attribute HTMLFormElement form;
           attribute DOMString keytype;
           attribute DOMString name;

  readonly attribute DOMString type;

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);

  readonly attribute NodeList labels;
};

The keygen element represents a key pair generator control. When the control's form is submitted, the private key is stored in the local keystore, and the public key is packaged and sent to the server.

The challenge attribute may be specified. Its value will be packaged with the submitted key.

The keytype attribute is an enumerated attribute. The following table lists the keywords and states for the attribute — the keywords in the left column map to the states listed in the cell in the second column on the same row as the keyword.

Keyword State
rsa RSA

The invalid value default state is the unknown state. The missing value default state is the RSA state.

The user agent may expose a user interface for each keygen element to allow the user to configure settings of the element's key pair generator, e.g. the key length.

The reset algorithm for keygen elements is to set these various configuration settings back to their defaults.

The element's value is the string returned from the following algorithm:

  1. Use the appropriate step from the following list:

    If the keytype attribute is in the RSA state

    Generate an RSA key pair using the settings given by the user, if appropriate.

    Select an RSA signature algorithm from those listed in section 7.2.1 ("RSA Signature Algorithm") of RFC2459. [RFC2459]

    Otherwise, the keytype attribute is in the unknown state

    The given key type is not supported. Return the empty string and abort this algorithm.

    Let private key be the generated private key.

    Let public key be the generated public key.

    Let signature algorithm be the selected signature algorithm.

  2. If the element has a challenge attribute, then let challenge be that attribute's value. Otherwise, let challenge be the empty string.

  3. Let algorithm be an ASN.1 AlgorithmIdentifier structure as defined by RFC2459, with the algorithm field giving the ASN.1 OID used to identify signature algorithm, using the OIDs defined in section 7.2 ("Signature Algorithms") of RFC2459, and the parameters field set up as required by RFC2459 for AlgorithmIdentifier structures for that algorithm. [X690] [RFC2459]

  4. Let spki be an ASN.1 SubjectPublicKeyInfo structure as defined by RFC2459, with the algorithm field set to the algorithm structure from the previous step, and the subjectPublicKey field set to the BIT STRING value resulting from ASN.1 DER encoding the public key. [X690] [RFC2459]

  5. Let publicKeyAndChallenge be an ASN.1 PublicKeyAndChallenge structure as defined below, with the spki field set to the spki structure from the previous step, and the challenge field set to the string challenge obtained earlier. [X690]

  6. Let signature be the BIT STRING value resulting from ASN.1 DER encoding the signature generated by applying the signature algorithm to the byte string obtained by ASN.1 DER encoding the publicKeyAndChallenge structure, using private key as the signing key. [X690]

  7. Let signedPublicKeyAndChallenge be an ASN.1 SignedPublicKeyAndChallenge structure as defined below, with the publicKeyAndChallenge field set to the publicKeyAndChallenge structure, the signatureAlgorithm field set to the algorithm structure, and the signature field set to the BIT STRING signature from the previous step. [X690]

  8. Return the result of base64 encoding the result of ASN.1 DER encoding the signedPublicKeyAndChallenge structure. [RFC3548] [X690]

The data objects used by the above algorithm are defined as follows. These definitions use the same "ASN.1-like" syntax defined by RFC2459. [RFC2459]

PublicKeyAndChallenge ::= SEQUENCE {
    spki SubjectPublicKeyInfo,
    challenge IA5STRING
}

SignedPublicKeyAndChallenge ::= SEQUENCE {
    publicKeyAndChallenge PublicKeyAndChallenge,
    signatureAlgorithm AlgorithmIdentifier,
    signature BIT STRING
}

Constraint validation: The keygen element is barred from constraint validation.

The form attribute is used to explicitly associate the keygen element with its form owner. The name attribute represents the element's name. The disabled attribute is used to make the control non-interactive and to prevent its value from being submitted. The autofocus attribute controls focus.

keygen . type

Returns the string "keygen".

The challenge and keytype DOM attributes must reflect the respective content attributes of the same name.

The type DOM attribute must return the value "keygen".

The willValidate, validity, and validationMessage attributes, and the checkValidity() and setCustomValidity() methods, are part of the constraint validation API. The labels attribute provides a list of the element's labels.

This specification does not specify how the private key generated is to be used. It is expected that after receiving the SignedPublicKeyAndChallenge (SPKAC) structure, the server will generate a client certificate and offer it back to the user for download; this certificate, once downloaded and stored in the key store along with the private key, can then be used to authenticate to services that use SSL and certificate authentication.

4.10.12 The output element

Categories
Flow content.
Phrasing content.
Listed and resettable form-associated element.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
for
form
name
DOM interface:
interface HTMLOutputElement : HTMLElement {
           attribute DOMString htmlFor;
  readonly attribute HTMLFormElement form;
           attribute DOMString name;

  readonly attribute DOMString type;
           attribute DOMString defaultValue;
           attribute DOMString value;

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);
};

The output element represents the result of a calculation.

The for content attribute allows an explicit relationship to be made between the result of a calculation and the elements that represent the values that went into the calculation or that otherwise influenced the calculation. The for attribute, if specified, must contain a string consisting of an unordered set of unique space-separated tokens, each of which must have the value of an ID of an element in the same Document.

The form attribute is used to explicitly associate the output element with its form owner. The name attribute represents the element's name.

The element has a value mode flag which is either value or default. Initially, the value mode flag must be set to default.

When the value mode flag is in mode default, the contents of the element represent both the value of the element and its default value. When the value mode flag is in mode value, the contents of the element represent the value of the element only, and the default value is only accessible using the defaultValue DOM attribute.

The element also has a default value. Initially, the default value must be the empty string.

Whenever the element's descendants are changed in any way, if the value mode flag is in mode default, the element's default value must be set to the value of the element's textContent DOM attribute.

The reset algorithm for output elements is to set the element's textContent DOM attribute to the value of the element's defaultValue DOM attribute (thus replacing the element's child nodes), and then to set the element's value mode flag to default.

output . value [ = value ]

Returns the element's current value.

Can be set, to change the value.

output . defaultValue [ = value ]

Returns the element's current default value.

Can be set, to change the default value.

output . type

Returns the string "output".

The value DOM attribute must act like the element's textContent DOM attribute, except that on setting, in addition, before the child nodes are changed, the element's value mode flag must be set to value.

The defaultValue DOM attribute, on getting, must return the element's default value. On setting, the attribute must set the element's default value, and, if the element's value mode flag is in the mode default, set the element's textContent DOM attribute as well.

The type attribute must return the string "output".

The htmlFor DOM attribute must reflect the for content attribute.

The willValidate, validity, and validationMessage attributes, and the checkValidity() and setCustomValidity() methods, are part of the constraint validation API.

Constraint validation: output elements are always barred from constraint validation.

4.10.13 Association of controls and forms

A form-associated element can have a relationship with a form element, which is called the element's form owner. If a form-associated element is not associated with a form element, its form owner is said to be null.

A form-associated element is, by default, associated with its nearest ancestor form element (as described below), but may have a form attribute specified to override this.

If a form-associated element has a form attribute specified, then its value must be the ID of a form element in the element's owner Document.

When a form-associated element is created, its form owner must be initialized to null (no owner).

When a form-associated element is to be associated with a form, its form owner must be set to that form.

When a form-associated element's ancestor chain changes, e.g. because it or one of its ancestors was inserted or removed from a Document, then the user agent must reset the form owner of that element.

When a form-associated element's form attribute is added, removed, or has its value changed, then the user agent must reset the form owner of that element.

When a form-associated element has a form attribute and the ID of any of the form elements in the Document changes, then the user agent must reset the form owner of that form-associated element.

When the user agent is to reset the form owner of a form-associated element, it must run the following steps:

  1. If the element's form owner is not null, and the element's form content attribute is not present, and the element's form owner is one of the ancestors of the element after the change to the ancestor chain, then do nothing, and abort these steps.

  2. Let the element's form owner be null.

  3. If the element has a form content attribute, then run these substeps:

    1. If the first element in the Document to have an ID that is equal to the element's form content attribute's value is a form element, then associate the form-associated element with that form element.

    2. Abort the "reset the form owner" steps.

  4. Otherwise, if the form-associated element in question has an ancestor form element, then associate the form-associated element with the nearest such ancestor form element.

  5. Otherwise, the element is left unassociated.

In the following non-conforming snippet:

...
 <form id="a">
  <div id="b"></div>
 </form>
 <script>
  document.getElementById('b').innerHTML =
     '<table><tr><td><form id="c"><input id="d"></table>' +
     '<input id="e">';
 </script>
...

The form owner of "d" would be the inner nested form "c", while the form owner of "e" would be the outer form "a".

This is because despite the association of "e" with "c" in the HTML parser, when the innerHTML algorithm moves the nodes from the temporary document to the "b" element, the nodes see their ancestor chain change, and thus all the "magic" associations done by the parser are reset to normal ancestor associations.

This example is a non-conforming document, though, as it is a violation of the content models to nest form elements.

element . form

Returns the element's form owner.

Returns null if there isn't one.

Form-associated elements have a form DOM attribute, which, on getting, must return the element's form owner, or null if there isn't one.

Constraint validation: If an element has no form owner, it is barred from constraint validation.

4.10.14 Attributes common to form controls

4.10.14.1 Naming form controls

The name content attribute gives the name of the form control, as used in form submission and in the form element's elements object. If the attribute is specified, its value must not be the empty string.

Constraint validation: If an element does not have a name attribute specified, or its name attribute's value is the empty string, then it is barred from constraint validation.

The name DOM attribute must reflect the name content attribute.

4.10.14.2 Enabling and disabling form controls

The disabled content attribute is a boolean attribute.

A form control is disabled if its disabled attribute is set, or if it is a descendant of a fieldset element whose disabled attribute is set.

A form control that is disabled must prevent any click events that are queued on the user interaction task source from being dispatched on the element.

Constraint validation: If an element is disabled, it is barred from constraint validation.

The disabled DOM attribute must reflect the disabled content attribute.

4.10.14.3 A form control's value

Form controls have a value and a checkedness. (The latter is only used by input elements.) These are used to describe how the user interacts with the control.

4.10.14.4 Autofocusing a form control

The autofocus content attribute allows the user to indicate that a control is to be focused as soon as the page is loaded, allowing the user to just start typing without having to manually focus the main control.

The autofocus attribute is a boolean attribute.

There must not be more than one element in the document with the autofocus attribute specified.

Whenever an element with the autofocus attribute specified is inserted into a document, the user agent should queue a task that checks to see if the element is focusable, and if so, runs the focusing steps for that element. User agents may also change the scrolling position of the document, or perform some other action that brings the element to the user's attention. The task source for this task is the DOM manipulation task source.

User agents may ignore this attribute if the user has indicated (for example, by starting to type in a form control) that he does not wish focus to be changed.

Focusing the control does not imply that the user agent must focus the browser window if it has lost focus.

The autofocus DOM attribute must reflect the content attribute of the same name.

In the following snippet, the text control would be focused when the document was loaded.

<input maxlength="256" name="q" value="" autofocus>
<input type="submit" value="Search">
4.10.14.5 Limiting user input length

A form control maxlength attribute, controlled by a dirty value flag declares a limit on the number of characters a user can input.

If an element has its form control maxlength attribute specified, the attribute's value must be a valid non-negative integer. If the attribute is specified and applying the rules for parsing non-negative integers to its value results in a number, then that number is the element's maximum allowed value length. If the attribute is omitted or parsing its value results in an error, then there is no maximum allowed value length.

Constraint validation: If an element has a maximum allowed value length, and its dirty value flag is false, and the code-point length of the element's value is greater than the element's maximum allowed value length, then the element is suffering from being too long.

User agents may prevent the user from causing the element's value to be set to a value whose code-point length is greater than the element's maximum allowed value length.

4.10.14.6 Form submission

Attributes for form submission can be specified both on form elements and on submit button (elements that represent buttons that submit forms, e.g. an input element whose type attribute is in the Submit Button state).

The attributes for form submission that may be specified on form elements are action, enctype, method, novalidate, and target.

The corresponding attributes for form submission that may be specified on submit button are formaction, formenctype, formmethod, formnovalidate, and formtarget. When omitted, they default to the values given on the corresponding attributes on the form element.


The action and formaction content attributes, if specified, must have a value that is a valid URL.

The action of an element is the value of the element's formaction attribute, if the element is a submit button and has such an attribute, or the value of its form owner's action attribute, if it has one, or else the empty string.


The method and formmethod content attributes are enumerated attributes with the following keywords and states:

The missing value default for these attributes is the GET state.

The method of an element is one of those four states. If the element is a submit button and has a formmethod attribute, then the element's method is that attribute's state; otherwise, it is the form owner's method attribute's state.


The enctype and formenctype content attributes are enumerated attributes with the following keywords and states:

The missing value default for these attributes is the application/x-www-form-urlencoded state.

The enctype of an element is one of those three states. If the element is a submit button and has a formenctype attribute, then the element's enctype is that attribute's state; otherwise, it is the form owner's enctype attribute's state.


The target and formtarget content attributes, if specified, must have values that are valid browsing context names or keywords.

The target of an element is the value of the element's formtarget attribute, if the element is a submit button and has such an attribute; or the value of its form owner's target attribute, if it has such an attribute; or, if one of the child nodes of the head element is a base element with a target attribute, then the value of the target attribute of the first such base element; or, if there is no such element, the empty string.


The novalidate and formnovalidate content attributes are boolean attributes. If present, they indicate that the form is not to be validated during submission.

The no-validate state of an element is true if the element is a submit button and the element's formnovalidate attribute is present, or if the element's form owner's novalidate attribute is present, and false otherwise.


The action, method, enctype, and target DOM attributes must reflect the respective content attributes of the same name. The noValidate DOM attribute must reflect the novalidate content attribute. The formAction DOM attribute must reflect the formaction content attribute. The formEnctype DOM attribute must reflect the formenctype content attribute. The formMethod DOM attribute must reflect the formmethod content attribute. The formNoValidate DOM attribute must reflect the formnovalidate content attribute. The formTarget DOM attribute must reflect the formtarget content attribute.

4.10.15 Constraints

4.10.15.1 Definitions

A listed form-associated element is a candidate for constraint validation unless a condition has barred the element from constraint validation. (For example, an element is barred from constraint validation if it is an output or fieldset element.)

An element can have a custom validity error message defined. Initially, an element must have its custom validity error message set to the empty string. When its value is not the empty string, the element is suffering from a custom error. It can be set using the setCustomValidity() method. The user agent should use the custom validity error message when alerting the user to the problem with the control.

An element can be constrained in various ways. The following is the list of validity states that a form control can be in, making the control invalid for the purposes of constraint validation. (The definitions below are non-normative; other parts of this specification define more precisely when each state applies or does not.)

Suffering from being missing

When a control has no value but has a required attribute (input required, textarea required).

Suffering from a type mismatch

When a control that allows arbitrary user input has a value that is not in the correct syntax (E-mail, URL).

Suffering from a pattern mismatch

When a control has a value that doesn't satisfy the pattern attribute.

Suffering from being too long

When a control has a value that is too long for the form control maxlength attribute (input maxlength, textarea maxlength).

Suffering from an underflow

When a control has a value that is too low for the min attribute.

Suffering from an overflow

When a control has a value that is too high for the max attribute.

Suffering from a step mismatch

When a control has a value that doesn't fit the rules given by the step attribute.

Suffering from a custom error

When a control's custom validity error message (as set by the element's setCustomValidity() method) is not the empty string.

An element can still suffer from these states even when the element is disabled; thus these states can be represented in the DOM even if validating the form during submission wouldn't indicate a problem to the user.

An element satisfies its constraints if it is not suffering from any of the above validity states.

4.10.15.2 Constraint validation

When the user agent is required to statically validate the constraints of form element form, it must run the following steps, which return either a positive result (all the controls in the form are valid) or a negative result (there are invalid controls) along with a (possibly empty) list of elements that are invalid and for which no script has claimed responsibility:

  1. Let controls be a list of all the submittable elements whose form owner is form, in tree order.

  2. Let invalid controls be an initially empty list of elements.

  3. For each element field in controls, in tree order, run the following substeps:

    1. If field is not a candidate for constraint validation, then move on to the next element.

    2. Otherwise, if field satisfies its constraints, then move on to the next element.

    3. Otherwise, add field to invalid controls.

  4. If invalid controls is empty, then return a positive result and abort these steps.

  5. Let unhandled invalid controls be an initially empty list of elements.

  6. For each element field in invalid controls, if any, in tree order, run the following substeps:

    1. Fire a simple event called invalid that is cancelable at field.

    2. If the event was not canceled, then add field to unhandled invalid controls.

  7. Return a negative result with the list of elements in the unhandled invalid controls list.

If a user agent is to interactively validate the constraints of form element form, then the user agent must run the following steps:

  1. Statically validate the constraints of form, and let unhandled invalid controls be the list of elements returned if the result was negative.

  2. If the result was positive, then return that result and abort these steps.

  3. Report the problems with the constraints of at least one of the elements given in unhandled invalid controls to the user. User agents may focus one of those elements in the process, by running the focusing steps for that element, and may change the scrolling position of the document, or perform some other action that brings the element to the user's attention. User agents may report more than one constraint violation. User agents may coalesce related constraint violation reports if appropriate (e.g. if multiple radio buttons in a group are marked as required, only one error need be reported). If one of the controls is not visible to the user (e.g. it has the hidden attribute set) then user agents may report a script error.

  4. Return a negative result.

4.10.15.3 The constraint validation API
element . willValidate

Returns true if the element will be validated when the form is submitted; false otherwise.

element . setCustomValidity(message)

Sets a custom error, so that the element would fail to validate. The given message is the message to be shown to the user when reporting the problem to the user.

If the argument is the empty string, clears the custom error.

element . validity . valueMissing

Returns true if the element has no value but is a required field; false otherwise.

element . validity . typeMismatch

Returns true if the element's value is not in the correct syntax; false otherwise.

element . validity . patternMismatch

Returns true if the element's value doesn't match the provided pattern; false otherwise.

element . validity . tooLong

Returns true if the element's value is longer than the provided maximum length; false otherwise.

element . validity . rangeUnderflow

Returns true if the element's value is lower than the provided minimum; false otherwise.

element . validity . rangeOverflow

Returns true if the element's value is higher than the provided maximum; false otherwise.

element . validity . stepMismatch

Returns true if the element's value doesn't fit the rules given by the step attribute; false otherwise.

element . validity . customError

Returns true if the element has a custom error; false otherwise.

element . validity . valid

Returns true if the element's value has no validity problems; false otherwise.

valid = element . checkValidity()

Returns true if the element's value has no validity problems; false otherwise. Fires an invalid event at the element in the latter case.

element . validationMessage

Returns the error message that would be shown to the user if the element was to be checked for validity.

The willValidate attribute must return true if an element is a candidate for constraint validation, and false otherwise (i.e. false if any conditions are barring it from constraint validation).

The setCustomValidity(message), when invoked, must set the custom validity error message to the value of the given message argument.

The validity attribute must return a ValidityState object that represents the validity states of the element. This object is live, and the same object must be returned each time the element's validity attribute is retrieved.

interface ValidityState {
  readonly attribute boolean valueMissing;
  readonly attribute boolean typeMismatch;
  readonly attribute boolean patternMismatch;
  readonly attribute boolean tooLong;
  readonly attribute boolean rangeUnderflow;
  readonly attribute boolean rangeOverflow;
  readonly attribute boolean stepMismatch;
  readonly attribute boolean customError;
  readonly attribute boolean valid;
};

A ValidityState object has the following attributes. On getting, they must return true if the corresponding condition given in the following list is true, and false otherwise.

valueMissing

The control is suffering from being missing.

typeMismatch

The control is suffering from a type mismatch.

patternMismatch

The control is suffering from a pattern mismatch.

tooLong

The control is suffering from being too long.

rangeUnderflow

The control is suffering from an underflow.

rangeOverflow

The control is suffering from an overflow.

stepMismatch

The control is suffering from a step mismatch.

customError

The control is suffering from a custom error.

valid

None of the other conditions are true.

When the checkValidity() method is invoked, if the element is a candidate for constraint validation and does not satisfy its constraints, the user agent must fire a simple event called invalid that is cancelable (but has no default action) at the element and return false. Otherwise, it must only return true without doing anything else.

The validationMessage attribute must return the empty string if the element is not a candidate for constraint validation or if it is one but it satisfies its constraints; otherwise, it must return a suitably localized message that the user agent would show the user if this were the only form with a validity constraint problem. If the element is suffering from a custom error, then the custom validity error message should be present in the return value.

4.10.15.4 Security

Servers should not rely on client-side validation. Client-side validation can be intentionally bypassed by hostile users, and unintentionally bypassed by users of older user agents or automated tools that do not implement these features. The constraint validation features are only intended to improve the user experience, not to provide any kind of security mechanism.

4.10.16 Form submission

4.10.16.1 Introduction

This section is non-normative.

...

4.10.16.2 Implicit submission

User agents may establish a button in each form as being the form's default button. This should be the first submit button in tree order whose form owner is that form element, but user agents may pick another button if another would be more appropriate for the platform. If the platform supports letting the user submit a form implicitly (for example, on some platforms hitting the "enter" key while a text field is focused implicitly submits the form), then doing so must cause the form's default button's activation behavior, if any, to be run.

Consequently, if the default button is disabled, the form is not submitted when such an implicit submission mechanism is used. (A button has no activation behavior when disabled.)

If the form has no submit button, then the implicit submission mechanism must just submit the form element from the form element itself.

4.10.16.3 Form submission algorithm

When a form form is submitted from an element submitter (typically a button), the user agent must run the following steps:

  1. If form is in a Document that has no associated browsing context or whose browsing context has its sandboxed forms browsing context flag set, then abort these steps without doing anything.

  2. If form is already being submitted (i.e. the form was submitted again while processing the events fired from the next two steps, probably from a script redundantly calling the submit() method on form), then abort these steps. This doesn't affect the earlier instance of this algorithm.

  3. If the submitter is anything but a form element, and the submitter element's no-validate state is false, then interactively validate the constraints of form and examine the result: if the result is negative (the constraint validation concluded that there were invalid fields and probably informed the user of this) then abort these steps.

  4. If the submitter is anything but a form element, then fire a simple event that is cancelable called submit, at form. If the event's default action is prevented (i.e. if the event is canceled) then abort these steps. Otherwise, continue (effectively the default action is to perform the submission).

  5. Let controls be a list of all the submittable elements whose form owner is form, in tree order.

  6. Let the form data set be a list of name-value-type tuples, initially empty.

  7. Constructing the form data set. For each element field in controls, in tree order, run the following substeps:

    1. If any of the following conditions are met, then skip these substeps for this element:

      • The field element has a datalist element ancestor.
      • The field element is disabled.
      • The field element is a button but it is not submitter.
      • The field element is an input element whose type attribute is in the Checkbox state and whose checkedness is false.
      • The field element is an input element whose type attribute is in the Radio Button state and whose checkedness is false.
      • The field element is an input element whose type attribute is in the File Upload state but the control does not have any files selected.
      • The field element is an object element that is not using a plugin.

      Otherwise, process field as follows:

    2. Let type be the value of the type DOM attribute of field.

    3. If the field element is an input element whose type attribute is in the Image Button state, then run these further nested substeps:

      1. If the field element has an name attribute specified and value is not the empty string, let name be that value followed by a single U+002E FULL STOP (.) character. Otherwise, let name be the empty string.

      2. Let namex be the string consisting of the concatenation of name and a single U+0078 LATIN SMALL LETTER X (x) character.

      3. Let namey be the string consisting of the concatenation of name and a single U+0079 LATIN SMALL LETTER Y (y) character.

      4. The field element is submitter, and before this algorithm was invoked the user indicated a coordinate. Let x be the x-component of the coordinate selected by the user, and let y be the y-component of the coordinate selected by the user.

      5. Append an entry in the form data set with the name namex, the value x, and the type type.

      6. Append an entry in the form data set with the name namey and the value y, and the type type.

      7. Skip the remaining substeps for this element: if there are any more elements in controls, return to the top of the constructing the form data set step, otherwise, jump to the next step in the overall form submission algorithm.

    4. If the field element does not have a name attribute specified, or its name attribute's value is the empty string, skip these substeps for this element: if there are any more elements in controls, return to the top of the constructing the form data set step, otherwise, jump to the next step in the overall form submission algorithm.

    5. Let name be the value of the field element's name attribute.

    6. If the field element is a select element, then for each option element in the select element whose selectedness is true, append an entry in the form data set with the name as the name, the value of the option element as the value, and type as the type.

    7. Otherwise, if the field element is an input element whose type attribute is in the Checkbox state or the Radio Button state, then run these further nested substeps:

      1. If the field element has a value attribute specified, then let value be the value of that attribute; otherwise, let value be the string "on".

      2. Append an entry in the form data set with name as the name, value as the value, and type as the type.

    8. Otherwise, if the field element is an input element whose type attribute is in the File Upload state, then for each file selected in the input element, append an entry in the form data set with the name as the name, the file (consisting of the name, the type, and the body) as the value, and type as the type.

    9. Otherwise, if the field element is an object element: try to obtain a form submission value from the plugin, and if that is successful, append an entry in the form data set with name as the name, the returned form submission value as the value, and the string "object" as the type.

    10. Otherwise, append an entry in the form data set with name as the name, the value of the field element as the value, and type as the type.

  8. Let action be the submitter element's action.

  9. If action is the empty string, let action be the document's address.

    This step is a willful violation of RFC 3986. [RFC3986]

  10. Resolve the URL action, relative to the submitter element. If this fails, abort these steps. Otherwise, let action be the resulting absolute URL.

  11. Let scheme be the <scheme> of the resulting absolute URL.

  12. Let enctype be the submitter element's enctype.

  13. Let method be the submitter element's method.

  14. Let target be the submitter element's target.

  15. Select the appropriate row in the table below based on the value of scheme as given by the first cell of each row. Then, select the appropriate cell on that row based on the value of method as given in the first cell of each column. Then, jump to the steps named in that cell and defined below the table.

    GET POST PUT DELETE
    http Mutate action Submit as entity body Submit as entity body Delete action
    https Mutate action Submit as entity body Submit as entity body Delete action
    ftp Get action Get action Get action Get action
    javascript Get action Get action Get action Get action
    data Get action Post to data: Put to data: Get action
    mailto Mail with headers Mail as body Mail with headers Mail with headers

    If scheme is not one of those listed in this table, then the behavior is not defined by this specification. User agents should, in the absence of another specification defining this, act in a manner analogous to that defined in this specification for similar schemes.

    The behaviors are as follows:

    Mutate action

    Let query be the result of encoding the form data set using the application/x-www-form-urlencoded encoding algorithm, interpreted as a US-ASCII string.

    Let destination be a new URL that is equal to the action except that its <query> component is replaced by query (adding a U+003F QUESTION MARK (?) character if appropriate).

    Let target browsing context be the form submission target browsing context.

    Navigate target browsing context to destination. If target browsing context was newly created for this purpose by the steps above, then it must be navigated with replacement enabled.

    Submit as entity body

    Let entity body be the result of encoding the form data set using the appropriate form encoding algorithm.

    Let target browsing context be the form submission target browsing context.

    Let MIME type be determined as follows:

    If enctype is application/x-www-form-urlencoded
    Let MIME type be "application/x-www-form-urlencoded".
    If enctype is multipart/form-data
    Let MIME type be "multipart/form-data".
    If enctype is text/plain
    Let MIME type be "text/plain".

    Navigate target browsing context to action using the HTTP method given by method and with entity body as the entity body, of type MIME type. If target browsing context was newly created for this purpose by the steps above, then it must be navigated with replacement enabled.

    Delete action

    Let target browsing context be the form submission target browsing context.

    Navigate target browsing context to action using the DELETE method. If target browsing context was newly created for this purpose by the steps above, then it must be navigated with replacement enabled.

    Get action

    Let target browsing context be the form submission target browsing context.

    Navigate target browsing context to action. If target browsing context was newly created for this purpose by the steps above, then it must be navigated with replacement enabled.

    Post to data:

    Let data be the result of encoding the form data set using the appropriate form encoding algorithm.

    If action contains the string "%%%%" (four U+0025 PERCENT SIGN characters), then %-escape all bytes in data that, if interpreted as US-ASCII, do not match the unreserved production in the URI Generic Syntax, and then, treating the result as a US-ASCII string, further %-escape all the U+0025 PERCENT SIGN characters in the resulting string and replace the first occurrence of "%%%%" in action with the resulting double-escaped string. [RFC3986]

    Otherwise, if action contains the string "%%" (two U+0025 PERCENT SIGN characters in a row, but not four), then %-escape all characters in data that, if interpreted as US-ASCII, do not match the unreserved production in the URI Generic Syntax, and then, treating the result as a US-ASCII string, replace the first occurrence of "%%" in action with the resulting escaped string. [RFC3986]

    Let target browsing context be the form submission target browsing context.

    Navigate target browsing context to the potentially modified action. If target browsing context was newly created for this purpose by the steps above, then it must be navigated with replacement enabled.

    Put to data:

    Let data be the result of encoding the form data set using the appropriate form encoding algorithm.

    Let MIME type be determined as follows:

    If enctype is application/x-www-form-urlencoded
    Let MIME type be "application/x-www-form-urlencoded".
    If enctype is multipart/form-data
    Let MIME type be "multipart/form-data".
    If enctype is text/plain
    Let MIME type be "text/plain".

    Let destination be the result of concatenating the following:

    1. The string "data:".
    2. The value of MIME type.
    3. The string ";base64,".
    4. A base-64 encoded representation of data. [RFC2045]

    Let target browsing context be the form submission target browsing context.

    Navigate target browsing context to destination. If target browsing context was newly created for this purpose by the steps above, then it must be navigated with replacement enabled.

    Mail with headers

    Let headers be the resulting encoding the form data set using the application/x-www-form-urlencoded encoding algorithm, interpreted as a US-ASCII string.

    Replace occurrences of U+002B PLUS SIGN characters (+) in headers with the string "%20".

    Let destination consist of all the characters from the first character in action to the character immediately before the first U+003F QUESTION MARK character (?), if any, or the end of the string if there are none.

    Append a single U+003F QUESTION MARK character (?) to destination.

    Append headers to destination.

    Let target browsing context be the form submission target browsing context.

    Navigate target browsing context to destination. If target browsing context was newly created for this purpose by the steps above, then it must be navigated with replacement enabled.

    Mail as body

    Let body be the resulting encoding the form data set using the appropriate form encoding algorithm and then %-escaping all the bytes in the resulting byte string that, when interpreted as US-ASCII, do not match the unreserved production in the URI Generic Syntax. [RFC3986]

    Let destination have the same value as action.

    If destination does not contain a U+003F QUESTION MARK character (?), append a single U+003F QUESTION MARK character (?) to destination. Otherwise, append a single U+0026 AMPERSAND character (&).

    Append the string "body=" to destination.

    Append body, interpreted as a US-ASCII string, to destination.

    Let target browsing context be the form submission target browsing context.

    Navigate target browsing context to destination. If target browsing context was newly created for this purpose by the steps above, then it must be navigated with replacement enabled.

    The form submission target browsing context is obtained, when needed by the behaviors described above, as follows: If the user indicated a specific browsing context to use when submitting the form, then that is the target browsing context. Otherwise, apply the rules for choosing a browsing context given a browsing context name using target as the name and the browsing context of form as the context in which the algorithm is executed; the resulting browsing context is the target browsing context.

    The appropriate form encoding algorithm is determined as follows:

    If enctype is application/x-www-form-urlencoded
    Use the application/x-www-form-urlencoded encoding algorithm.
    If enctype is multipart/form-data
    Use the multipart/form-data encoding algorithm.
    If enctype is text/plain
    Use the text/plain encoding algorithm.
4.10.16.4 URL-encoded form data

The application/x-www-form-urlencoded encoding algorithm is as follows:

  1. Let result be the empty string.

  2. If the form element has an accept-charset attribute, then, taking into account the characters found in the form data set's names and values, and the character encodings supported by the user agent, select a character encoding from the list given in the form's accept-charset attribute that is an ASCII-compatible character encoding. If none of the encodings are supported, then let the selected character encoding be UTF-8.

    Otherwise, if the document's character encoding is an ASCII-compatible character encoding, then that is the selected character encoding.

    Otherwise, let the selected character encoding be UTF-8.

  3. Let charset be the preferred MIME name of the selected character encoding.

  4. If the entry's name is "_charset_" and its type is "hidden", replace its value with charset.

  5. If the entry's type is "file", replace its value with the file's filename only.

  6. For each entry in the form data set, perform these substeps:

    1. For each character in the entry's name and value that cannot be expressed using the selected character encoding, replace the character by a string consisting of a U+0026 AMPERSAND character (&), a U+0023 NUMBER SIGN character (#), one or more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) representing the Unicode code point of the character in base ten, and finally a U+003B SEMICOLON character (;).

    2. For each character in the entry's name and value, apply the following subsubsteps:

      1. If the character isn't in the range U+0020, U+002A, U+002D, U+002E, U+0030 .. U+0039, U+0041 .. U+005A, U+005F, U+0061 .. U+007A then replace the character with a string formed as follows: Start with the empty string, and then, taking each byte of the character when expressed in the selected character encoding in turn, append to the string a U+0025 PERCENT SIGN character (%) followed by two characters in the ranges U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) and U+0041 LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z representing the hexadecimal value of the byte (zero-padded if necessary).

      2. If the character is a U+0020 SPACE character, replace it with a single U+002B PLUS SIGN character (+).

    3. If the entry's name is "isindex", its type is "text", and this is the first entry in the form data set, then append the value to result and skip the rest of the substeps for this entry, moving on to the next entry, if any, or the next step in the overall algorithm otherwise.

    4. If this is not the first entry, append a single U+0026 AMPERSAND character (&) to result.

    5. Append the entry's name to result.

    6. Append a single U+003D EQUALS SIGN character (=) to result.

    7. Append the entry's value to result.

  7. Encode result as US-ASCII and return the resulting byte stream.

4.10.16.5 Multipart form data

The multipart/form-data encoding algorithm is to encode the form data set using the rules described by RFC2388, Returning Values from Forms: multipart/form-data, and return the resulting byte stream. [RFC2388]

Each entry in the form data set is a field, the name of the entry is the field name and the value of the entry is the field value.

The order of parts must be the same as the order of fields in the form data set. Multiple entries with the same name must be treated as distinct fields.

4.10.16.6 Plain text form data

The text/plain encoding algorithm is as follows:

  1. Let result be the empty string.

  2. If the form element has an accept-charset attribute, then, taking into account the characters found in the form data set's names and values, and the character encodings supported by the user agent, select a character encoding from the list given in the form's accept-charset attribute. If none of the encodings are supported, then let the selected character encoding be UTF-8.

    Otherwise, the selected character encoding is the document's character encoding.

  3. Let charset be the preferred MIME name of the selected character encoding.

  4. If the entry's name is "_charset_" and its type is "hidden", replace its value with charset.

  5. If the entry's type is "file", replace its value with the file's filename only.

  6. For each entry in the form data set, perform these substeps:

    1. Append the entry's name to result.

    2. Append a single U+003D EQUALS SIGN character (=) to result.

    3. Append the entry's value to result.

    4. Append a U+000D CARRIAGE RETURN (CR) U+000A LINE FEED (LF) character pair to result.

  7. Encode result using the selected character encoding and return the resulting byte stream.

4.10.17 Resetting a form

When a form form is reset, the user agent must invoke the reset algorithm of each resettable elements whose form owner is form, and must then broadcast formchange events from form.

Each resettable element defines its own reset algorithm. Changes made to form controls as part of these algorithms do not count as changes caused by the user (and thus, e.g., do not cause input events to fire).

4.10.18 Event dispatch

When the user agent is to broadcast forminput events or broadcast formchange events from a form element form, it must run the following steps:

  1. Let controls be a list of all the resettable elements whose form owner is form.

  2. If the user agent was to broadcast forminput events, let event name be forminput. Otherwise the user agent was to broadcast formchange events; let event name be formchange.
  3. For each element in controls, in tree order, fire a simple event called event name at the element.

4.11 Interactive elements

4.11.1 The details element

Categories
Flow content.
Interactive content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
One legend element followed by flow content.
Content attributes:
Global attributes
open
DOM interface:
interface HTMLDetailsElement : HTMLElement {
           attribute boolean open;
};

The details element represents additional information or controls which the user can obtain on demand.

The details element is not appropriate for footnotes. Please see the section on footnotes for details on how to mark up footnotes.

The first element child of a details element, if it is a legend element, represents the summary of the details.

If the first element is not a legend element, the UA should provide its own legend (e.g. "Details").

The open content attribute is a boolean attribute. If present, it indicates that the details are to be shown to the user. If the attribute is absent, the details are not to be shown.

If the attribute is removed, then the details should be hidden. If the attribute is added, the details should be shown.

The user agent should allow the user to request that the details be shown or hidden. To honor a request for the details to be shown, the user agent must set the open attribute on the element to the value open. To honor a request for the details to be hidden, the user agent must remove the open attribute from the element.

The open attribute must reflect the open content attribute.

4.11.2 The datagrid element

Categories
Flow content.
Interactive content.
Sectioning root.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Either: Nothing.
Or: Flow content, but where the first element child node, if any, is not a table, select, or datalist element.
Or: A single table element.
Or: A single select element.
Or: A single datalist element.
Content attributes:
Global attributes
disabled
DOM interface:
interface HTMLDataGridElement : HTMLElement {
           attribute boolean multiple;
           attribute boolean disabled;
           attribute DataGridListener listener;

  // columns
  void addColumn(in Column id, in DOMString label, in DOMString type, [Optional] in HTMLImageElement icon, [Optional] in boolean sortable, [Optional] in boolean visible);
           attribute DOMString sortColumn;
           attribute boolean sortAscending;
  void clearColumns();

  // rows
  void renotify();
  void setRowCount(in long childCount, in long rowCount);
  void setRows(in RowList rows);
  void insertRows(in RowList rows);
  void deleteRows(in RowIDList rows);
  void repaint(in RowID row, in DOMString column);
  void clearRows();

};

typedef DOMString Column;
typedef sequence<Column> ColumnList;
typedef sequence<any> Cell; // Column, [Variadic] any (exact types expected depend on the column type)
typedef sequence<Cell> CellList;
typedef sequence<any> Row; // RowID, long, long, CellList, [Optional] boolean, [Optional] long
typedef sequence<Row> RowList;
typedef sequence<unsigned long> RowID;
typedef sequence<RowID> RowIDList;

[Callback=FunctionOnly, NoInterfaceObject]
interface RenderingContext2DCallback {
  DOMString handleEvent(in CanvasRenderingContext2D context, in unsigned long width, in unsigned long height);
};

The datagrid element represents an interactive representation of tree, list, or tabular data.

The data being presented is provided by script using the methods described in the following sections.

The disabled attribute is a boolean attribute used to disable the control. When the attribute is set, the user agent must disable the datagrid, preventing the user from interacting with it. The datagrid element should still continue to update itself when the underlying data changes, though, as described in the next few sections. However, conformance requirements stating that datagrid elements must react to users in particular ways do not apply when the datagrid is disabled.

The disabled DOM attribute must reflect the content attribute of the same name.

4.11.2.1 Introduction

This section is non-normative.

In the datagrid data model, data is structured as a set of rows representing a tree, each row being split into a number of columns. The columns are always present in the data model, although individual columns might be hidden in the presentation.


Each row can have child rows. Child rows may be hidden or shown, by closing or opening (respectively) the parent row.

Rows are referred to by the path along the tree that one would take to reach the row, using zero-based indices. Thus, the first row of a list is row "0", the second row is row "1"; the first child row of the first row is row "0,0", the second child row of the first row is row "0,1"; the fourth child of the seventh child of the third child of the tenth row is "9,2,6,3", etc.

The chains of numbers that give a row's path, or identifier, are represented by arrays of positions, represented in IDL by the RowID interface.

The root of the tree is represented by an empty array.


Each column has a string that is used to identify it in the API, a label that is shown to users interacting with the column, a type, and optionally an icon.

The possible types are as follows:

Keyword Description
text Simple text.
editable Editable text.
checkable Text with a check box.
list A list of values that the user can switch between.
progress A progress bar.
meter A gauge.
custom A canvas onto which arbitrary content can be drawn.

Each column can be flagged as sortable, in which case the user will be able to sort the view using that column.

Columns are not necessarily visible. A column can be created invisible by default. The user can select which columns are to be shown.

When no columns have been added to the datagrid, a column with no name, whose identifier is the empty string, whose type is text, and which is not sortable, is implied. This column is removed if any explicit columns are declared.

Each cell uses the type given for its column, so all cells in a column present the same type of information.

4.11.2.1.1 Example: a datagrid backed by a static table element

...

4.11.2.1.2 Example: a datagrid backed by nested ol elements

...

4.11.2.1.3 Example: a datagrid backed by a server

...

4.11.2.2 Populating the datagrid
datagrid . listener [ = value ]

Return the current object that is configured as the datagrid listener, if any. Returns null if there is none.

The listener is an object provided by the script author that receives notifications when the datagrid needs row data to render itself, when the user opens and closes rows with children, when the user edits a cell, and when the user invokes a row's context menu. (The DataGridListener interface used for this purpose is described in the next section.)

Can be set, to change the current listener.

datagrid . renotify()

Causes the datagrid to resend notifications to the listener (if any) for any rows or cells that the datagrid does not yet have information for.

datagrid . addColumn(id, label, type [, icon [, sortable [, visible ] ] ] )

Adds a column to the datagrid.

If a column with the given identifier has already been added, it just replaces the information for that column.

The possible types are enumerated in the previous section.

datagrid . sortColumn [ = value ]

Returns the identifier of the column by which the data is to be sorted.

Can be set, to indicate that the sort order has changed. This will cause the datagrid to clear its position information for rows, so setRows() will have to be called again with the new sort order.

The columns are not actually sorted by the datagrid; the data has to be sorted by the script that adds the rows to the datagrid.

datagrid . sortAscending [ = value ]

Returns true if the data is to be sorted with smaller values first; otherwise, returns false, indicating that bigger values are to be put first.

Can be set, to indicate that the order is about to change.

datagrid . clearColumns()

Removes all the columns in the datagrid, reinstating the implied column.

datagrid . setRowCount(childCount, rowCount)

Sets the numbers of rows in the datagrid, excluding rows that are descendants of rows that are closed.

Throws a DATAGRID_MODEL_ERR exception if the arguments contradict each other or previously declared information (e.g. declaring that the datagrid has three rows when the 12th row has been declared).

datagrid . setRows(rows)

Updates data for rows in the datagrid, or fills in data for rows previously implied by a call to setRowCount() but not previously declared.

The rows argument is an array of rows, each represented by a further array consisting of:

  1. A RowID object identifying the row.
  2. An integer giving the position of the row in its parent, given the current sort order, or −1 to set other row data without setting a position or changing a previously declared position.
  3. An integer giving the number of children of the row, or 0 if the row has no children, or −1 if the row has children but the count is currently unknown. If the number of children has already been set to 0 or a positive integer, then passing −1 leaves the previous count unchanged.
  4. An array giving the data for zero or more cells in the row, as described below.
  5. A boolean declaring whether the row is open or not. This entry, if omitted, is assumed to be false (closed), unless the row has already been declared as open.
  6. An integer giving the number of rows that are descendants of this row, excluding those that are descendants of descendants of this row that are closed. This entry can be omitted if the row is closed or if it has already been declared.

The array giving the data for the cells in the row consists of a further set of arrays, one per cell. The first item of each of these arrays is the column's identifier; the subsequent values vary based on the type of the column, as follows:

text
  1. A string giving the cell's value.
  2. Optionally, an img element giving an icon for the cell.
editable
  1. A string giving the cell's value.
  2. Optionally, a datalist element giving a set of predefined options.
  3. Optionally, an img element giving an icon for the cell.
checkable
  1. A string giving the cell's value.
  2. A boolean, indicating whether the cell is checked (true) or not (false).
  3. Optionally, a boolean indicating whether the value of the cell is obscured as indeterminate (true), or not (false).
  4. Optionally, an img element giving an icon for the cell.
list
  1. A string giving the cell's current value.
  2. A select element giving the list of options.
  3. Optionally, an img element giving an icon for the cell.
progress
  1. A value in the range 0.0 (no progress) to 1.0 (task complete).
meter
  1. A number giving the cell's value.
  2. Optionally, a number giving the maximum value, if it's not 1.
  3. Optionally, a number giving the minimum value, if it's not 0.
  4. Optionally, a number giving the highest value that is considered "low".
  5. Optionally, a number giving the lowest value that is considered "high".
  6. Optionally, a number giving the value that is considered optimal.
custom
  1. A number giving the minimum width of the cell, in CSS pixels, that is desired.
  2. A number giving the minimum height of the cell, in CSS pixels, that is desired.
  3. A function that is passed a CanvasRenderingContext2D object, along with the width and height (in CSS pixels) of the cell that the context will draw on.

While the rows in a single call to the setRows() method can be in any order, for each row, it is important that all its ancestor rows and all its open previous siblings are also declared, either in the same call or in an earlier one.

Throws a DATAGRID_MODEL_ERR exception if the arguments contradict each other or previously declared information (e.g. saying that a row's position is 5 when the parent row only has 3 children, or naming a column that doesn't exist, or declaring a row without declaring its parent, or changing the number of children that a row has while that row and its ancestors are all open).

datagrid . insertRows(rows)

Inserts the given rows into the datagrid, increasing the numbers of rows that the datagrid assumes are present.

The rows argument is an array of rows in the same structure as the argument to the setRows() method described above, with the same expectations of consistency (a given row's ancestors and earlier open siblings being listed either earlier or in the same call as a given row). However, unlike with the setRows() method, if a row is inserted along with its child, the child is not included in the child and row counts of the parent row; every row in the rows argument will increase its parent's counts automatically.

Throws a DATAGRID_MODEL_ERR exception if the arguments contradict each other or previously declared information.

datagrid . deleteRows(rows)

Removes the given rows from the datagrid, and updates the number of rows known to be in the datagrid accordingly. The argument is an array of RowID objects identifying the rows to remove.

Throws a DATAGRID_MODEL_ERR exception if the argument includes a row the datagrid doesn't know about.

datagrid . repaint(row, column)

If the given column's type is custom, then causes the datagrid to reinvoke the function that obtains the desired rendering.

datagrid . clearRows()

Clears the datagrid of all row data, resetting it to empty.

4.11.2.2.1 The listener

The listener DOM attribute allows authors to specify an object that will receive all the notifications from the datagrid. Initially, its value must be null. On getting, it must return its value. On setting, its value must be set to the new value, and then the user agent must queue a task to call the initialize() method with the datagrid element as its only argument.

4.11.2.2.2 The columns

The columns are represented by the column list, an ordered list of entries for columns, each of which consists of:

An identifier
A string used to identify the column in the API.
A label
A string used in the user interface.
A type
One of the types described below.
An icon
An image, copied from an img element when the column was declared.
Whether the column is sortable
A boolean indicating whether the user can request that the data be sorted by this column (true), or not (false).
Whether the column is visible
A boolean indicating whether the column is part of the datagrid's rendering.

Initially, the column list must have a single column, the default column, whose identifier is the empty string, whose label is the empty string, whose type is text, with no icon, which is not sortable, and which is visible.


The addColumn(id, label, type, icon, sortable, visible) method must run the following steps:

  1. If there is already an entry in column list, other than the default column, whose identifier is id, throw a DATAGRID_MODEL_ERR exception and abort these steps.

  2. If type is not a string equal to one of the allowed datagrid column types, then throw a DATAGRID_MODEL_ERR exception and abort these steps.

  3. If the icon argument is present and not null, and the given img element's complete attribute is false, then throw an INVALID_STATE_ERR exception and abort these steps.

  4. If the icon argument is present and not null, then copy the image data from that img element, and let image be the copy of that image data. Otherwise, let image be nothing.

  5. Append a new entry to the column list, with id as its identifier, label as its label, type as its type, and image as its icon. Let the column be sortable if the sortable argument is present and true, and make it visible if the visible argument is absent or true.

  6. If the column list contains the default column, then remove the default column from the column list, discard any data for cells in that column in any rows in the datagrid, set sortColumn to id, set sortAscending to true, and run the datagrid resort steps.


The sortColumn DOM attribute gives the current column used for sorting. Initially, its value must be the empty string. On getting, it must return its current value. On setting, if the new value doesn't match the identifier of one of the columns in the column list, then the user agent must throw a DATAGRID_MODEL_ERR exception. Otherwise, if the new value is not the same as its current value, then the user agent must set the attribute to the new value, and then run the datagrid resort steps.

The sortAscending DOM attribute specifies the direction that the tree is sorted in, ascending (true) or descending (false). Initially, its value must be true (ascending). On getting, it must return its current value. On setting, if the new value is not the same as its current value, then the user agent must set the attribute to the new value, and then run the datagrid resort steps.

When a column is marked as being sortable, the user agent should allow the user to select that column to be the column used for sorting, and should allow the user to chose whether the sort order is ascending or descending.

When the user changes the sort order in this manner, the user agent must update the sortColumn and sortAscending attributes appropriately, and then run the datagrid resort steps.

The datagrid resort steps are described in the next section.


The clearColumns() method, if the column list doesn't contain the default column, must empty the column list, append the default column to the now empty column list, discard any data for cells in all rows in the datagrid, set sortColumn to the empty string, set sortAscending to true, and run the datagrid resort steps. (If the column list is already just the default column, then the method does nothing.)

4.11.2.2.3 The rows

A datagrid element is intended to show a representation of a tree, where typically the user only sees a small part of the tree at a time.

To make this efficient, the datagrid element actually shows a small part of a sparse tree, so that only relevant parts of the data structure need be loaded at any time. Specifically, the model requires only that all the ancestor rows of the displayed rows be loaded, as well as any open earlier siblings (in the displayed sort order) of the displayed rows.

Conceptually, therefore, a datagrid has a number of related sparse data structures backing it.

The first is the natural order sparse data tree. This is the structure in which rows are entered as they are declared, in their natural order. This can differ from the order actually displayed to the user. It consists of nested sparse lists of rows. In the natural order sparse data tree, a row will always have all its parents already declared. Once a row is added to this structure, it can only be removed by the deleteRows() and clearRows() methods. The order of nodes in this tree never changes; to move a node in this tree, it has to be removed and then another row (with the same data) reinserted elsewhere.

The second structure is the display order sparse data tree. This is a similar structure that contains a subset of the rows in the natural order sparse data tree, ordered in the order given by the sortAscending and sortColumn attributes, and excluding rows with one or more ancestors that are closed. This tree is cleared whenever the sortAscending and sortColumn attributes change.

The third structure is the display order sparse data list. This structure is a flattened representation of the display order sparse data tree.

At any time, a number of consecutive rows in the display order sparse data list are physically visible to the user. The datagrid fires notifications to a listener (provided by script), and the listener, or other some script, is expected to feed the datagrid with the information needed to render the control.

A datagrid has a pending datagrid rows list, which is a list of rows in the display order sparse data list for which the datagrid has sent notifications requesting information but not yet received information about.

A datagrid also has a pending datagrid cells list, which is a list of row/column pairs (cells) for which the datagrid has sent notifications requesting information but not yet received information about.

User agents may discard information about rows that are not displayed and that are not ancestors or open earlier siblings of rows or ancestors of rows that are displayed.


These structures are different views of the collection of rows that form the datagrid. Each row has the following information associated with it:

A parent

Either another row, or the datagrid itself. This is the parent of the row in the natural order sparse data tree and the display order sparse data tree for the datagrid.

A natural order position relative to the other rows with the same parent

This is the number of rows that precede this row under the same parent in the natural order sparse data tree. This number can't be changed relative to other rows in the same parent; to change the relative natural order of data in the datagrid, the original rows have to be removed and new rows (with the same data but different natural positions) inserted in their place. (The exact number of a row can change, as new rows can be inserted above it.)

A row can be identified by a RowID object. This is an array of numbers, consisting of the natural order positions of each ancestor row and the row itself, starting from the furthest ancestor. Thus, for instance, the fourth child row of the first child row of the second row in a datagrid would be identified by a RowID object whose value is [1, 0, 3]. A row's identifier changes if rows are inserted before it in the datagrid.

A display order position relative to the other rows with the same parent

This is the number of rows that precede this row under the same parent in the display order sparse data tree. This number can be unknown. If the sort order changes, then this information is lost (as the display order sparse data tree is cleared).

A child count

The number of rows that have this row as a parent. If this is zero, the row cannot be opened. If this is −1, then the child count is unknown but the row can be opened. This value can be changed by the setRows() method only if the current value is −1 or if the row or one of its ancestors is closed. Otherwise, it can only be changed indirectly using the insertRows() and deleteRows() methods.

An open flag

A boolean indicating whether the row is open (true) or closed (false). Once set, the flag can only be changed by the user or while one of the row's ancestors is itself closed. A row can also be in a third state, "opening", which is treated as closed for all purposes except that the user agent may indicate that the row is in this special state, and except that when the row is updated to have a row count, the row will switch to being open.

A row count

The number of rows that have this row as a parent or ancestor, and that do not have an ancestor that is a descendant of this row that is itself closed. If this is −1, then the row count is unknown. This value can be changed by the setRows() method only if the row or one of its ancestors is closed (or opening, but not open). Otherwise, it can only be changed indirectly using the insertRows() and deleteRows() methods.

Cells

The data that applies to this row. Cell data is discussed in more detail below.

The datagrid itself also has a child count and a row count, which are analogous to the child counts and row counts for rows. Initially, these must be zero.


The datagrid resort steps, which are invoked when the sort order changes as described in the previous section, are as follows:

  1. Clear the display order sparse data tree (i.e. mark the display order position of all the rows in the datagrid as unknown).

    User agents may cache the position information of rows for various values of sortColumn and sortAscending, instead of discarding the information altogether. If the user agent caches this information, and has information that applies to the current values of sortColumn and sortAscending, then the user agent may repopulate the display order sparse data tree from this information.

  2. Clear the pending datagrid rows list and the pending datagrid cells list.

  3. Invoke the datagrid update display algorithm.


The renotify() method must empty the pending datagrid rows list and the pending datagrid cells list, and invoke the datagrid update display algorithm.


The setRowCount(childCount, rowCount) method must run the following steps:

  1. Set the datagrid child count to childCount, the datagrid row count to rowCount.

  2. Audit the datagrid. If this fails, then revert the changes made in the previous step, throw a DATAGRID_MODEL_ERR exception, and abort these steps.

  3. Invoke the datagrid update display algorithm.


The setRows(rows) method must run the following steps:

  1. Type-check the rows argument. If this fails, throw a TypeError exception, and abort these steps.

  2. Partially sort the rows argument.

  3. For each Row object in the rows argument, in order, perform the appropriate steps from the list below.

    The changes made to the datagrid's data structures in this step get reverted (as required below) if any consistency errors are detected either in this step or the next.

    If there already exists a row in the datagrid's natural order sparse data tree with the same identifier as given by the Row object's RowID object, and that row and all its ancestors are open

    If one of the following conditions is true, then revert all the changes done in this step, throw a DATAGRID_MODEL_ERR exception, and abort these steps:

    • The value of the Row object's second entry is neither −1 nor equal to the child count of the preexisting row.
    • The Row object has fewer than four entries or more than six entries.
    • The Row object has five or more entries, and its fifth entry is false.
    • The Row object has six entries, and its sixth entry is not equal to the row count of the preexisting row.
    If there already exists a row in the datagrid's natural order sparse data tree with the same identifier as given by the Row object's RowID object, but either that row or one of its ancestors is closed

    Set the preexisting row's child count to the value of the Row object's second entry.

    If the Row object has five or more entries, and either its fifth entry is true and the preexisting row is closed but not opening, or its fifth entry is false and the preexisting row is open, then: if the preexisting row has no ancestor row that is closed, then revert all the changes done in this step, throw a DATAGRID_MODEL_ERR exception, and abort these steps; otherwise, if the fifth entry is false, then close the row; otherwise, open the row.

    If the Row object has six entries, set the preexisting row's row count to the value of the Row object's sixth entry.

    If the preexisting row is opening, then: increase the datagrid row count and the row counts of any ancestor rows by the number of rows that the preexisting row now has in its row count, then open the row.

    There does not exist a row in the datagrid's natural order sparse data tree with the same identifier as given by the Row object's RowID object

    If the RowID object has a length greater than 1, then verify that there is a row identified by the RowID consisting of all but the last number in the Row object's RowID. If there is no such row present in the natural order sparse data tree, then revert all the changes done in this step, throw a DATAGRID_MODEL_ERR exception, and abort these steps.

    Create a row and insert it into the natural order sparse data tree, such that its parent is the row identified by the RowID consisting of all but the last number in the Row object's RowID, or the datagrid if the length of the Row object's RowID is 1; with its natural order position being the last number of the Row object's RowID; with the child count being the value of the third entry of the Row object; with the row being marked closed unless the Row object has five or more entries and its fifth entry is true, in which case the row is open; and with its row count being −1 unless the Row object has six entries, in which case the row count is equal to the value of the Row object's sixth entry.

  4. Audit the datagrid. If this fails, then revert the changes made in the previous step, throw a DATAGRID_MODEL_ERR exception, and abort these steps.

  5. For each Row object in the rows argument, in order, apply the Row object.

  6. Invoke the datagrid update display algorithm.


The insertRows(rows) method must run the following steps:

  1. Type-check the rows argument. If this fails, throw a TypeError exception, and abort these steps.

  2. Partially sort the rows argument.

  3. For each Row object in the rows argument, in order, run the following steps:

    The changes made to the datagrid's data structures in this step get reverted (as required below) if any consistency errors are detected either in this step or the next.

    1. Let parent be the row identified by the RowID consisting of all but the last number in the Row object's RowID, or the datagrid itself if the Row object's RowID has length 0.

      If there is no such row present in the natural order sparse data tree, then revert all the changes done in this algorithm, throw a DATAGRID_MODEL_ERR exception, and abort these steps.

    2. Increment by one the natural order position of all rows whose parent is parent and whose natural order position is equal to or greater than the last number of the Row object's RowID.

    3. If the value of the Row object's second entry is not −1, then increment by one the display order position of all rows whose parent is parent and whose display order position is equal to or greater than the value of the Row object's second entry.

    4. Create a row and insert it into the natural order sparse data tree, such that its parent is parent; with its natural order position being the last number of the Row object's RowID; with the child count being the value of the third entry of the Row object; with the row being marked closed unless the Row object has five or more entries and its fifth entry is true, in which case the row is open; and with its row count being −1 unless the Row object has six entries, in which case the row count is equal to the value of the Row object's sixth entry.

  4. For each Row object in the rows argument, in order, apply the Row object.

  5. Invoke the datagrid update display algorithm.


When an algorithm requires the user agent to type-check a RowList object (an array), each entry in the object must be checked against the following requirements. If any are false, then the type-check fails, otherwise it passes.

Where the above requirements say that a value is to be a string, the user agent must apply the ToString() conversion operator to the value, assume that the value was indeed a string, and use the result in the rest of the algorithm as if it had that had been the value passed to the method. [ECMA262]

Where the above requirements say that a value is to be a number, the user agent must first apply the ToNumber() conversion operator to the value, and then verify that the result is neither the not-a-number NaN value nor an infinite value. If this result is indeed acceptable (i.e. finite), the user agent must use the result in the rest of the algorithm as if it had that had been the value passed to the method. [ECMA262]

Where the above requirements say that a value is to be an integer, the user agent must first apply the ToNumber() conversion operator to the value, and then verify that the result is a finite integer. If so, the user agent must use the result in the rest of the algorithm as if it had that had been the value passed to the method. [ECMA262]

Where the above requirements say that a value is to be a boolean, the user agent must apply the ToBoolean() conversion operator to the value, assume that the value was indeed a boolean, and use the result in the rest of the algorithm as if it had that had been the value passed to the method. [ECMA262]


When an algorithm requires the user agent to audit the datagrid, the datagrid must be checked against the following requirements. If any are false, then the audit fails, otherwise it passes.

For the purposes of this audit, the datagrid must be treated as the parent row of all the rows that are direct children of the datagrid in the natural order sparse data tree and the display order sparse data tree. The child count of this implied row is the datagrid child count, and the row count of this implied row is the datagrid row count.


When an algorithm requires the user agent to partially sort a RowList object (an array), the entries in the object must be resorted such that Row objects are listed after any of their ancestors and after any of their earlier siblings. In other words, for any two Row objects a and b in the RowList, where a is before b after the sort, the following conditions must hold:


The deleteRows(rows) method must run the following steps:

  1. If any of the entries in rows are not RowID objects consisting of one or more entries whose values are all integers that are greater than or equal to zero, then throw a TypeError exception and abort these steps.

    To check if a value is an integer, the user agent must first apply the ToNumber() conversion operator to the value, and then verify that the result is a finite integer. If so, the user agent must use the result in the rest of the algorithm as if it had that had been the value passed to the method. [ECMA262]

  2. If any of the RowID objects in the rows argument identify a row that isn't present in the natural order sparse data tree, then throw a DATAGRID_MODEL_ERR exception and abort these steps.

  3. If any row is listed twice in the rows argument, then throw a DATAGRID_MODEL_ERR exception and abort these steps.

  4. Sort the rows argument such that the entries are given in the same order as the rows they identify would be visited in a pre-order, depth first traversal of the natural order sparse data tree.

  5. For each row identified by entries in rows, in reverse order, run the following steps:

    1. Decrement the child count of the row's parent row, if that child count is greater than zero. If the row has no parent, decrement the datagrid child count.

      If the row has a parent row, and its child count is now zero, then close that row.

    2. Let delta be one more than the row's row count if the row is open and its row count is greater than zero; otherwise, let delta be one.

    3. Let ancestor be the row.

    4. Row count loop: Let ancestor be ancestor's parent row, if any, or null if it has none.

    5. If ancestor is null, then decrement the datagrid row count by delta. Otherwise, if ancestor is open, then decrement its row count by delta.

    6. If ancestor is not null, then jump back to the step labeled row count loop above.

    7. Let parent be the row's parent, or the datagrid if the row has no parent.

    8. Decrement by one the natural order position of all rows whose parent is parent and whose natural order position is equal to or greater than the row's own natural order position.

    9. If the row is in the display order sparse data tree, then decrement by one the display order position of all rows whose parent is parent and whose display order position is equal to or greater than the row's own display order position.

    10. Clear the row and its descendants from the Datagrid.

  6. Invoke the datagrid update display algorithm.


The clearRows() method must empty the natural order sparse data tree, reset both the datagrid child count and the datagrid row count to zero, and invoke the datagrid update display algorithm.


The repaint(row, column) method must cause the user agent to clear its cache for the cell specified by the identifier row and the column column, if that column's type is custom. If the given column has not been declared, or its type is not custom, then the user agent must throw a DATAGRID_MODEL_ERR exception. If the given row is not known, then the method must do nothing. If the cell is indeed cleared, the user agent must reinvoke the previously registered RenderingContext2DCallback callback when it needs to repaint that row.


If a row has a child count that isn't zero, then the user agent should offer to the user the option of opening and closing the row.

When a row is opened, if the row's row count is greater than zero, then the user agent must increase the datagrid row count and the row counts of any ancestor rows by the number of rows that the newly opened row has in its row count, then must mark the row as open, then may fill in the display order sparse data tree with any information that the user agent has cached about the display order positions of descendants of the newly opened row, and then must invoke the rowOpened() method on the current listener with as its first argument a RowID object identifying the row that was opened and as its second argument the boolean false, and then must invoke the datagrid update display algorithm.

On the other hand, when a row is opened and the row's row count is −1, then the user agent must mark the row as opening, and then must invoke the rowOpened() method on the current listener with as its first argument a RowID object identifying the row that was opened and as its second argument the boolean true.

When a row is closed, the user agent must decrease the datagrid row count and the row counts of any ancestor rows by the number of rows that the newly closed row has in its row count, and then must invoke the rowOpened() method on the current listener with as its first and only argument a RowID object identifying the row that was opened.

4.11.2.2.4 The cells

Each row has one cell per column. Each cell has the same type as its column. The allowed datagrid column types, what they represent, and the requirements for when the user interacts with them, are as follows:

text

The cell represents some text and an optional image.

editable

The cells represents some editable text, an optional datalist giving autocompletion hints, and an optional image.

If there is a datalist element, the user agent should offer the suggestions represented by that element to the user. The user agent may use the suggestion's label to identify the suggestion. If the user selects a suggestion, then the editable text must be set to the selected suggestion's value, as if the user had written that value himself.

When the user edits the value, either directly or using the datalist, the user agent must invoke the cellChanged() method on the current listener with as its first argument a RowID identifying the cell's row, as its second argument the identifier of the cell's column, as its third argument the new value, and as its fourth argument the previous value.

checkable

The cell represents some text, a check box that optionally has its value obscured as indeterminate, and an optional image.

When the user checks or unchecks the check box, the user agent must change the check box's state appropriately and stop obscuring the check box as indeterminate (if it is obscuring it), and then must invoke the cellChanged() method on the current listener with as its first argument a RowID identifying the cell's row, as its second argument the identifier of the cell's column, as its third argument true if the check box is now checked and false otherwise, and as its fourth argument true if the check box was previously checked and false otherwise.

list

The cell represents some text giving the current value selected from a dropdown list of options, a select element giving the list of options, and an optional image.

The user agent should allow the user to change the value of the cell from its current value to one of the values given by option elements in the list of options (if any). The user agent may use the option elements' labels to annotate each option.

When the user selects a new value from the select element's list of options, the user agent must invoke the cellChanged() method on the current listener with as its first argument a RowID identifying the cell's row, as its second argument the identifier of the cell's column, as its third argument the new value, and as its fourth argument the previous value.

progress

The cell represents a (determinate) progress bar whose value is between 0.0, indicating no progress, and 1.0, indicating the task is complete.

meter

The cell represents a gauge, described by one to six numbers.

The gauge's actual value is given by the first number.

If there is a second number, then that number is the maximum value. Otherwise, the maximum value is 1.0.

If there is a third number, then that number is the minimum value. Otherwise, the minimum value is 1.0.

If there is a fourth number, then that number is the low boundary. Otherwise, the low boundary is the minimum value.

If there is a fifth number, then that number is the high boundary. Otherwise, the high boundary is the maximum value.

If there is a sixth number, then the optimal point is the sixth number. Otherwise, the optimum point is the midpoint between the minimum value and the maximum value.

If the optimum point is equal to the low boundary or the high boundary, or anywhere in between them, then the region between the low and high boundaries of the gauge must be treated as the optimum region, and the low and high parts, if any, must be treated as suboptimal. Otherwise, if the optimum point is less than the low boundary, then the region between the minimum value and the low boundary must be treated as the optimum region, the region between the low boundary and the high boundary must be treated as a suboptimal region, and the region between the high boundary and the maximum value must be treated as an even less good region. Finally, if the optimum point is higher than the high boundary, then the situation is reversed; the region between the high boundary and the maximum value must be treated as the optimum region, the region between the high boundary and the low boundary must be treated as a suboptimal region, and the remaining region between the low boundary and the minimum value must be treated as an even less good region.

User agents should indicate the relative position of the actual value to the minimum and maximum values, and the relationship between the actual value and the three regions of the gauge.

custom

The cell represents a dynamically generated graphical image.

The cell will have minimum dimensions (specified in CSS pixels), and a callback (in the form of a RenderingContext2DCallback object) to get a rendering for the cell.

The user agent should not allow the cell to be rendered with dimensions less than the given minimum width and height.

When the user agent needs to render the cell, the user agent must queue a task to invoke the RenderingContext2DCallback callback, passing it a newly created CanvasRenderingContext2D object whose canvas DOM attribute is null as the first argument, the actual cell width in CSS pixels as the second argument, and the actual cell height in CSS pixels as the third argument.

If the user agent is able to render graphics, then it must render the graphics commands that the callback executed on the provided CanvasRenderingContext2D object onto the cell once the callback returns. The image must be clipped to the dimensions of the cell. The coordinate space of the cell must be aligned with that used by the 2D context such that the top left corner of the cell is the 0,0 origin, with the coordinate space increasing its x dimension towards the right of the cell and its y axis towards the bottom of the cell, and with the image not scaled (so that one CSS pixel on the final rendering matches one CSS pixel in the coordinate space used by the 2D context).

The user agent must then decouple the CanvasRenderingContext2D object and any objects that it created (such as CanvasPattern objects or ImageData objects) from any real drawing surface.

If the user agent is unable to render graphics, then it must render the text string returned by the callback instead.


When an algorithm requires the user agent to apply a Row object, the user agent must run the following steps:

  1. If the value of the Row object's second entry is not −1, then run these substeps:

    1. If there is a row with the same parent as the row specified by the Row object's RowID object, whose display order position is currently the same as the value of the Row object's second entry, then remove that row from the display order sparse data tree.

    2. Set the display order position of the row specified by the Row object's RowID to the value of the Row object's second entry, updating its position in the display order sparse data tree accordingly.

    3. If the row is in the pending datagrid rows list, remove it.

  2. If the fourth entry in the Row object (a CellList object, an array) is not empty, then for each Cell object in that array update the cell that corresponds to the column identified by the value of the first entry of the Cell object, by using the appropriate set of steps given below as determined by the type of the column. Then, if the cell is in the pending datagrid cells list, remove it.

    If the column's type is text

    Update the cell's text to the value given in the Cell object's second entry.

    If the Cell object has three entries, then copy the image data from the img element given in the third entry, and let the cell's image be given by that image data. Otherwise, update the cell to have no image.

    If the column's type is editable

    Update the cell's text to the value given in the Cell object's second entry.

    If the Cell object has three entries, then let the datalist element given in the third entry be the datalist element giving autocompletion hints. Otherwise, update the cell to have no datalist element.

    If the Cell object has four entries, then copy the image data from the img element given in the fourth entry, and let the cell's image be given by that image data. Otherwise, update the cell to have no image.

    If the column's type is checkable

    Update the cell's text to the value given in the Cell object's second entry.

    Update the cell's checked state to match the value of the third entry: checked if true, unchecked otherwise.

    If the Cell object has four entries and the fourth entry is true, then update the cell to be obscured as indeterminate. Otherwise, the cell's state is not obscured.

    If the Cell object has five entries, then copy the image data from the img element given in the fifth entry, and let the cell's image be given by that image data. Otherwise, update the cell to have no image.

    If the column's type is list

    Update the cell's text to the value given in the Cell object's second entry, and the select element to be the one given in the Cell object's third entry

    If the Cell object has four entries, then copy the image data from the img element given in the fourth entry, and let the cell's image be given by that image data. Otherwise, update the cell to have no image.

    If the column's type is progress

    Update the cell to be a progress bar whose progress, on the scale of 0.0 (no progress) to 1.0 (task complete) is given by the value in the Cell object's second entry.

    If the column's type is meter

    Update the cell to be a gauge configured with the numbers given by the second and subsequent entries of the Cell object.

    If the column's type is custom

    Update the cell's minimum width to be the length in CSS pixels given by the Cell object's second entry.

    Update the cell's minimum height to be the length in CSS pixels given by the Cell object's third entry.

    Update the cell's callback to be the RenderingContext2DCallback object given by the Cell object's fourth entry.


When the user agent is to run the datagrid update display algorithm, the user agent must invoke the getRows() and getCells() methods on the current listener such that all the current visible rows in the display order sparse data list, and all the cells in the currently visible columns on all the currently visible rows, have been covered.

A row is considered covered if it is present in the pending datagrid rows list, or if the getRows() method is invoked with a range that includes the row in question.

A cell is considered covered if it is present in the pending datagrid cells list, or if the getRows() method is invoked with a range that includes the row in question and a list of columns that includes the cell's column, or if the getCells() method is invoked with a list of rows and columns that intersects the cell in question. However, the getCells() method can only be used if the row is already present in the display order sparse data list.

The getRows() method, if used, must be invoked with five arguments. The first argument must be the index in the display order sparse data list to the first row that the user agent is requesting, known as the anchor row. The second argument must be the number of consecutive cells for which the user agent is requesting information. The third argument must be the RowID of the row that is the nearest ancestor in the display order sparse data tree of the anchor row. If this is the datagrid, then the RowID object must be an empty array. The fourth argument must be the display order position of the anchor row in the display order sparse data tree, assuming that the row identified in the third argument is indeed the anchor row's parent row. The fifth and final argument must be an array of the identifiers of the columns for which the user agent is requesting information, in the order they were added to the datagrid.

As the getRows() method is invoked, the pending datagrid rows list must be updated to include the rows for which information has been requested, excluding rows for which information is already available; and the pending datagrid cells list must be updated to include the cells for which information has been requested on those rows.

The getCells() method, if used, must be invoked with two arguments. The first argument must be an array of RowID objects identifying the rows for which information is being requested. The second argument must be an array of the identifiers of the columns for which the user agent is requesting information, in the order they were added to the datagrid.

As the getCells() method is invoked, the pending datagrid cells list must be updated to include the cells for which information has been requested.

Calls to these methods should be batched so that the rows and cells to be covered are handled by the fewest number of calls to these methods as possible. To this end, user agents may invoke the getRows() method for a set of rows that includes some rows that are already in the display order sparse data list, and similarly may invoke the getCells() method with row/column combinations that cover some cells for which data is already known. Generally, however, user agents should avoid invoking these methods with arguments that cause information to be requested when it has already been requested or is already known.

For example, consider a case represented by the following table, where the cells marked "Yes" indicate that the data has already been obtained, the cells marked "Pending" indicate that the data has been previously requested but not yet obtained, and the cells with just a dash indicate that no information has ever been obtained, or any information that had been obtained has now been discarded.

Row Column A Column B
Row 1 - - -
Row 2 Yes Yes Yes
Row 3 Yes Yes Yes
Row 4 Yes Yes Yes
Row 5 - - -
Row 6 - - -
Row 7 Yes Pending -
Row 8 Yes Pending Pending

Thus, rows 2, 3, 4, 7, and 8 are already covered, as are the cells from those rows except for the cell in column B of row 7.

Now consider what happens if all of these rows become visible at once. The user agent has several choices, including (but not limited to) the following:

All three options are allowed, but the latter two are preferable to the former, as they minimise the amount of redundant information requested.

In any case, the data model now looks like this:

Row Column A Column B Column C
Row 1 Pending Pending Pending -
Row 2 Yes Yes Yes -
Row 3 Yes Yes Yes -
Row 4 Yes Yes Yes -
Row 5 Pending Pending Pending -
Row 6 Pending Pending Pending -
Row 7 Yes Pending Pending -
Row 8 Yes Pending Pending -

Now consider the case where a third column, column C, is added to the data model. The user agent once again has several choices, including (but not limited to) the following:

The two options here are as bad as each other; the former involves a lot of overlap, but the latter involves a lot of method calls. Unfortunately the user agent can't do the obvious thing, namely just to invoke the getCells() method for all the rows listing just column C, because it doesn't have the row information for all the rows yet (rows 1, 5 and 6 are still pending).

In any case, the data model now looks like this:

Row Column A Column B Column C
Row 1 Pending Pending Pending Pending
Row 2 Yes Yes Yes Pending
Row 3 Yes Yes Yes Pending
Row 4 Yes Yes Yes Pending
Row 5 Pending Pending Pending Pending
Row 6 Pending Pending Pending Pending
Row 7 Yes Pending Pending Pending
Row 8 Yes Pending Pending Pending

If at this point the user scrolls around anywhere within this datagrid, the user agent won't fire the getRos() and getCells() methods, because all of the rows and cells are covered.

Now consider the case where the user agent receives row information, but no cell information, for rows 1, 5, and 6:

Row Column A Column B Column C
Row 1 Yes Pending Pending Pending
Row 2 Yes Yes Yes Pending
Row 3 Yes Yes Yes Pending
Row 4 Yes Yes Yes Pending
Row 5 Yes Pending Pending Pending
Row 6 Yes Pending Pending Pending
Row 7 Yes Pending Pending Pending
Row 8 Yes Pending Pending Pending

The user agent still won't fire any methods when the user scrolls, because the data is still covered. But if the script then calls the renotify() method, the "Pending" flags would get reset, and the model would now look like this:

Row Column A Column B Column C
Row 1 Yes - - -
Row 2 Yes Yes Yes -
Row 3 Yes Yes Yes -
Row 4 Yes Yes Yes -
Row 5 Yes - - -
Row 6 Yes - - -
Row 7 Yes - - -
Row 8 Yes - - -

Now, assuming that all eight rows and all three columns are still visible, the user agent has the following choices (amongst others):

Here the latter two are preferable because they result in less overlap than the first.


The task source for tasks queued on behalf of a datagrid is the DOM manipulation task source.

4.11.2.3 Listening to notifications from the datagrid

The conformance criteria in this section apply to any implementation of the DataGridListener interface, including (and most commonly) the content author's implementation(s).

// To be implemented by Web authors as a JS object
[NoInterfaceObject] interface DataGridListener {
  void initialize(in HTMLDataGridElement datagrid);

  void getRows(in unsigned long rowIndex, in unsigned long rowCount, in RowID parentRow, in unsigned long position, in ColumnList columns);
  void getCells(in RowIDList rows, in ColumnList columns);
  void rowOpened(in RowID row, in boolean rowCountNeeded);
  void rowClosed(in RowID row);

  void cellChanged(in RowID row, in Column column, in any newValue, in any prevValue);
  HTMLMenuElement getRowMenu(in RowID row);
};

The DataGridDataProvider interface, once implemented by an object in a script and hooked up to a datagrid using the data DOM attribute, receives notifications when the datagrid needs information (such as which rows exist) for display.

The following methods may be usefully implemented:

initialize(datagrid)

Called by the datagrid element (the one given by the datagrid argument) when the listener attribute is set.

getRows(rowIndex, rowCount, parentRow, position, columns)

Called by the datagrid element when the user agent finds itself needing to render rows for which it is lacking information.

The rowIndex argument gives the flattened index of the first row for which it needs information, ignoring the tree structure of the datagrid model, where zero is the first row of the entire tree.

The rowCount argument gives the number of rows for which the user agent would like information.

The parentRow argument gives the RowID object identifying the nearest ancestor of the first row that the user agent is aware of. After the sort order has changed, this will typically be the root of the tree (identified by a RowID object consisting of an empty array).

The columns argument gives the columns for which the user agent is lacking information, as an array of column identifiers (as passed to addColumn()).

getCells(rows, columns)

Called by the datagrid element when the user agent finds itself needing to render cells for which it is lacking information in rows that it does know about.

The rows argument gives an array of RowID objects identifying the various rows for which the user agent is lacking information.

The columns argument gives the columns for which the user agent is lacking information, as an array of column identifiers (as passed to addColumn()).

rowOpened(row, rowCountNeeded)

Called by the datagrid element when the user has opened a row.

The row argument gives an RowID object identifying the row that was opened.

If the user agent also knows how many children that row has, then the rowCountNeeded argument will be false. Otherwise, the argument will be true, and the row will remain closed until the setRows() method is called with an accurate row count.

rowClosed(row)

Called by the datagrid element when the user has opened a row.

The row argument gives an RowID object identifying the row that was closed.

cellChanged(row, column, newValue, prevValue)

Called by the datagrid element when the user has edited a cell or checked a check box in a cell.

The row argument gives an RowID object identifying the row of the cell, and the column argument gives the identifier of the cell's column.

The newValue argument gives the new value, and the prevValue argument gives the previous value.

getRowMenu(row)
Must return an HTMLMenuElement object that is to be used as a context menu for row row, or null if there is no particular context menu. May be omitted if none of the rows have a special context menu. As this method is called immediately before showing the menu in question, no precautions need to be taken if the return value of this method changes.

Objects that implement the DataGridListener interface may omit any or all of the methods. When a method is omitted, a user agent intending to call that method must instead skip the method call, and must assume that the method's return value is null.

4.11.3 The command element

Categories
Metadata content.
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where metadata content is expected.
Where phrasing content is expected.
Content model:
Empty.
Content attributes:
Global attributes
type
label
icon
disabled
checked
radiogroup
default
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLCommandElement : HTMLElement {
           attribute DOMString type;
           attribute DOMString label;
           attribute DOMString icon;
           attribute boolean disabled;
           attribute boolean checked;
           attribute DOMString radiogroup;
           attribute boolean default;
 void click(); // shadows HTMLElement.click()
};

The Command interface must also be implemented by this element.

The command element represents a command that the user can invoke.

The type attribute indicates the kind of command: either a normal command with an associated action, or a state or option that can be toggled, or a selection of one item from a list of items.

The attribute is an enumerated attribute with three keywords and states. The keyword "command" maps to the Command state, the checkbox" maps to the Checkbox, and the "radio" keyword maps to the Radio state. The missing value default is the Command state.

The Command state

The element represents a normal command with an associated action.

The Checkbox state

The element represents a state or option that can be toggled.

The Radio state

The element represents a selection of one item from a list of items.

The label attribute gives the name of the command, as shown to the user.

The title attribute gives a hint describing the command, which might be shown to the user to help him.

The icon attribute gives a picture that represents the command. If the attribute is specified, the attribute's value must contain a valid URL. To obtain the absolute URL of the icon, the attribute's value must be resolved relative to the element.

The disabled attribute is a boolean attribute that, if present, indicates that the command is not available in the current state.

The distinction between disabled and hidden is subtle. A command would be disabled if, in the same context, it could be enabled if only certain aspects of the situation were changed. A command would be marked as hidden if, in that situation, the command will never be enabled. For example, in the context menu for a water faucet, the command "open" might be disabled if the faucet is already open, but the command "eat" would be marked hidden since the faucet could never be eaten.

The checked attribute is a boolean attribute that, if present, indicates that the command is selected. The attribute must be omitted unless the type attribute is in either the Checkbox state or the Radio state.

The radiogroup attribute gives the name of the group of commands that will be toggled when the command itself is toggled, for commands whose type attribute has the value "radio". The scope of the name is the child list of the parent element. The attribute must be omitted unless the type attribute is in the Radio state.

If the command element is used when generating a context menu, then the default attribute indicates, if present, that the command is the one that would have been invoked if the user had directly activated the menu's subject instead of using its context menu. The default attribute is a boolean attribute. The attribute must be omitted unless the type attribute is in the Command state.

Need an example that shows an element that, if double-clicked, invokes an action, but that also has a context menu, showing the various command attributes off, and that has a default command.

The type, label, icon, disabled, checked, radiogroup, and default DOM attributes must reflect the respective content attributes of the same name.

The click() method's behavior depends on the value of the type attribute of the element, as follows:

If the type attribute is in the Checkbox state

If the element has a checked attribute, the UA must remove that attribute. Otherwise, the UA must add a checked attribute, with the literal value checked. The UA must then fire a click event at the element.

If the type attribute is in the Radio state

If the element has a parent, then the UA must walk the list of child nodes of that parent element, and for each node that is a command element, if that element has a radiogroup attribute whose value exactly matches the current element's (treating missing radiogroup attributes as if they were the empty string), and has a checked attribute, must remove that attribute and fire a click event at the element.

Then, the element's checked attribute attribute must be set to the literal value checked and a click event must be fired at the element.

Otherwise

The UA must fire a click event at the element.

Firing a synthetic click event at the element does not cause any of the actions described above to happen.

command elements are not rendered unless they form part of a menu.

4.11.4 The bb element

Categories
Flow content.
Phrasing content.
Interactive content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content, but there must be no interactive content descendant.
Content attributes:
Global attributes
type
DOM interface:
interface HTMLBrowserButtonElement : HTMLElement {
           attribute DOMString type;
  readonly attribute boolean supported;
  readonly attribute boolean disabled;
};

The Command interface must also be implemented by this element.

The bb element represents a user agent command that the user can invoke.

The type attribute indicates the kind of command. The type attribute is an enumerated attribute. The following table lists the keywords and states for the attribute — the keywords in the left column map to the states listed in the cell in the second column on the same row as the keyword.

Keyword State
makeapp make application

The missing value default state is the null state.

Each state has an action and a relevance, defined in the following sections.

When the attribute is in the null state, the action is to not do anything, and the relevance is unconditionally false.

A bb element whose type attribute is in a state whose relevance is true must be enabled. Conversely, a bb element whose type attribute is in a state whose relevance is false must be disabled.

If a bb element is enabled, it will match the :enabled pseudo-class; otherwise, it will match the :disabled pseudo-class.

User agents should allow users to invoke bb elements when they are enabled. When a user invokes a bb element, its type attribute's state's action must be invoked.

When the element has no descendant element children and has no descendant text node children of non-zero length, the element represents a browser button with a user-agent-defined icon or text representing the type attribute's state's action and relevance (enabled vs disabled). Otherwise, the element represents its children.

bb . supported

Returns true if the value in the type attribute is a value that the user agent supports. Otherwise, returns false.

bb . disabled

Returns false if the user can invoke the element's action (i.e. if the element's relevance is true). Otherwise, returns true.

The type DOM attribute must reflect the content attribute of the same name.

The supported DOM attribute must return true if the type attribute is in a state other than the null state and the user agent supports that state's action (i.e. when the attribute's value is one that the user agent recognizes and supports), and false otherwise.

The disabled DOM attribute must return true if the element is disabled, and false otherwise (i.e. it returns the opposite of the type attribute's state's relevance).

4.11.4.1 Browser button types
4.11.4.1.1 The make application state

Some user agents support making sites accessible as independent applications, as if they were not Web sites at all. The make application state exists to allow Web pages to offer themselves to the user as targets for this mode of operation.

The action of the make application state is to confirm the user's intent to use the current site in a standalone fashion, and, provided the user's intent is confirmed, offer the user a way to make the resource identified by the document's address available in such a fashion.

The confirmation is needed because it is relatively easy to trick users into activating buttons. The confirmation could, e.g. take the form of asking the user where to "save" the application, or non-modal information panel that is clearly from the user agent and gives the user the opportunity to drag an icon to their system's application launcher.

The relevance of the make application state is false if the user agent is already handling the site in such a fashion, or if the user agent doesn't support making the site available in that fashion, and true otherwise.

In the following example, a few links are listed on an application's page, to allow the user perform certain actions, including making the application standalone:

<menu>
 <li><a href="settings.html" onclick="panels.show('settings')">Settings</a>
 <li><bb type="makeapp">Download standalone application</bb>
 <li><a href="help.html" onclick="panels.show('help')">Help</a>
 <li><a href="logout.html" onclick="panels.show('logout')">Sign out</a>
</menu>

With the following stylesheet, it could be make to look like a single line of text with vertical bars separating the options, with the "make app" option disappearing when it's not supported or relevant:

menu li { display: none; }
menu li:enabled { display: inline; }
menu li:not(:first-child)::before { content: ' | '; }

This could look like this:

"Settings | Download standalone application | Help | Sign out"

The following example shows another way to do the same thing as the previous one, this time not relying on CSS support to hide the "make app" link if it doesn't apply:

<menu>
 <a href="settings.html" onclick="panels.show('settings')">Settings</a> |
 <bb type="makeapp" id="makeapp"> </bb>
 <a href="help.html" onclick="panels.show('help')">Help</a> |
 <a href="logout.html" onclick="panels.show('logout')">Sign out</a>
</menu>
<script>
 var bb = document.getElementById('makeapp');
 if (bb.supported && bb.enabled) {
   bb.parentNode.nextSibling.textContent = ' | ';
   bb.textContent = 'Download standalone application';
 } else {
   bb.parentNode.removeChild(bb);
 }
</script>
Categories
Flow content.
If the element's type attribute is in the tool bar state: Interactive content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Either: Zero or more li elements.
Or: Flow content.
Content attributes:
Global attributes
type
label
DOM interface:
interface HTMLMenuElement : HTMLElement {
           attribute DOMString type;
           attribute DOMString label;
};

The menu element represents a list of commands.

The type attribute is an enumerated attribute indicating the kind of menu being declared. The attribute has three states. The context keyword maps to the context menu state, in which the element is declaring a context menu. The toolbar keyword maps to the tool bar state, in which the element is declaring a tool bar. The attribute may also be omitted. The missing value default is the list state, which indicates that the element is merely a list of commands that is neither declaring a context menu nor defining a tool bar.

If a menu element's type attribute is in the context menu state, then the element represents the commands of a context menu, and the user can only interact with the commands if that context menu is activated.

If a menu element's type attribute is in the tool bar state, then the element represents a list of active commands that the user can immediately interact with.

If a menu element's type attribute is in the list state, then the element either represents an unordered list of items (each represented by an li element), each of which represents a command that the user can perform or activate, or, if the element has no li element children, flow content describing available commands.

The label attribute gives the label of the menu. It is used by user agents to display nested menus in the UI. For example, a context menu containing another menu would use the nested menu's label attribute for the submenu's menu label.

The type and label DOM attributes must reflect the respective content attributes of the same name.

This section is non-normative.

...

4.11.5.2 Building menus and tool bars

A menu (or tool bar) consists of a list of zero or more of the following components:

The list corresponding to a particular menu element is built by iterating over its child nodes. For each child node in tree order, the required behavior depends on what the node is, as follows:

An element that defines a command
Append the command to the menu, respecting its facets. If the element is a command element with a default attribute, mark the command as being a default command.
An hr element
An option element that has a value attribute set to the empty string, and has a disabled attribute, and whose textContent consists of a string of one or more hyphens (U+002D HYPHEN-MINUS)
Append a separator to the menu.
An li element
Iterate over the children of the li element.
A menu element with no label attribute
A select element
Append a separator to the menu, then iterate over the children of the menu or select element, then append another separator.
A menu element with a label attribute
An optgroup element
Append a submenu to the menu, using the value of the element's label attribute as the label of the menu. The submenu must be constructed by taking the element and creating a new menu for it using the complete process described in this section.
Any other node
Ignore the node.

We should support label in the algorithm above -- just iterate through the contents like with li, to support input elements in label elements. Also, optgroup elements without labels should be ignored (maybe? or at least should say they have no label so that they are dropped below), and select elements inside label elements may need special processing.

Once all the nodes have been processed as described above, the user agent must the post-process the menu as follows:

  1. Any menu item with no label, or whose label is the empty string, must be removed.
  2. Any sequence of two or more separators in a row must be collapsed to a single separator.
  3. Any separator at the start or end of the menu must be removed.
4.11.5.3 Context menus

The contextmenu attribute gives the element's context menu. The value must be the ID of a menu element in the DOM. If the node that would be obtained by the invoking the getElementById() method using the attribute's value as the only argument is null or not a menu element, then the element has no assigned context menu. Otherwise, the element's assigned context menu is the element so identified.

When an element's context menu is requested (e.g. by the user right-clicking the element, or pressing a context menu key), the UA must fire a simple event called contextmenu that bubbles and is cancelable at the element for which the menu was requested.

Typically, therefore, the firing of the contextmenu event will be the default action of a mouseup or keyup event. The exact sequence of events is UA-dependent, as it will vary based on platform conventions.

The default action of the contextmenu event depends on whether the element has a context menu assigned (using the contextmenu attribute) or not. If it does not, the default action must be for the user agent to show its default context menu, if it has one.

Context menus should inherit (so clicking on a span in a paragraph with a context menu should show the menu).

If the element does have a context menu assigned, then the user agent must fire a simple event called show at the menu element. Actually this should fire an event that has modifier information (shift/ctrl etc), as well as having a pointer to the node on which the menu was fired, and with which the menu was associated (which could be an ancestor of the former).

The default action of this event is that the user agent must show a context menu built from the menu element.

The user agent may also provide access to its default context menu, if any, with the context menu shown. For example, it could merge the menu items from the two menus together, or provide the page's context menu as a submenu of the default menu.

If the user dismisses the menu without making a selection, nothing in particular happens.

If the user selects a menu item that represents a command, then the UA must invoke that command's Action.

Context menus must not, while being shown, reflect changes in the DOM; they are constructed as the default action of the show event and must remain like that until dismissed.

User agents may provide means for bypassing the context menu processing model, ensuring that the user can always access the UA's default context menus. For example, the user agent could handle right-clicks that have the Shift key depressed in such a way that it does not fire the contextmenu event and instead always shows the default context menu.

The contextMenu attribute must reflect the contextmenu content attribute.

4.11.5.4 Tool bars

When a menu element has a type attribute in the tool bar state, then the user agent must build the menu for that menu element, and use the result in the rendering.

The user agent must reflect changes made to the menu's DOM, by immediately rebuilding the menu.

4.11.6 Commands

A command is the abstraction behind menu items, buttons, and links. Once a command is defined, other parts of the interface can refer to the same command, allowing many access points to a single feature to share aspects such as the disabled state.

Commands are defined to have the following facets:

Type
The kind of command: "command", meaning it is a normal command; "radio", meaning that triggering the command will, amongst other things, set the Checked State to true (and probably uncheck some other commands); or "checkbox", meaning that triggering the command will, amongst other things, toggle the value of the Checked State.
ID
The name of the command, for referring to the command from the markup or from script. If a command has no ID, it is an anonymous command.
Label
The name of the command as seen by the user.
Hint
A helpful or descriptive string that can be shown to the user.
Icon
An absolute URL identifying a graphical image that represents the action. A command might not have an Icon.
Hidden State
Whether the command is hidden or not (basically, whether it should be shown in menus).
Disabled State
Whether the command is relevant and can be triggered or not.
Checked State
Whether the command is checked or not.
Action
The actual effect that triggering the command will have. This could be a scripted event handler, a URL to which to navigate, or a form submission.

Commands are represented by elements in the DOM. Any element that can define a command also implements the Command interface:

Actually even better would be to just mix it straight into those interfaces somehow.

[NoInterfaceObject] interface Command {
  readonly attribute DOMString commandType;          
  readonly attribute DOMString id;
  readonly attribute DOMString label;
  readonly attribute DOMString title;
  readonly attribute DOMString icon;
  readonly attribute boolean hidden;
  readonly attribute boolean disabled;              
  readonly attribute boolean checked;              
  void click();
};

The Command interface must be implemented by any element capable of defining a command. All the attributes of the Command interface are read-only. Elements implementing this interface might implement other interfaces that have attributes with identical names but that are mutable; in bindings that flatten all supported interfaces on the object, the mutable attributes must shadow the readonly attributes defined in the Command interface.

element . commandType

Exposes the Type facet of the command.

element . id

Exposes the ID facet of the command.

element . label

Exposes the Label facet of the command.

element . title

Exposes the Hint facet of the command.

element . icon

Exposes the Icon facet of the command.

element . hidden

Exposes the Hidden State facet of the command.

element . disabled

Exposes the Disabled State facet of the command.

element . checked

Exposes the Checked State facet of the command.

element . click

Triggers the Action of the command.

The commandType attribute must return a string whose value is either "command", "radio", or "checked", depending on whether the Type of the command defined by the element is "command", "radio", or "checked" respectively. If the element does not define a command, it must return null.

The id attribute must return the command's ID, or null if the element does not define a command or defines an anonymous command. This attribute will be shadowed by the id DOM attribute on the HTMLElement interface.

The label attribute must return the command's Label, or null if the element does not define a command or does not specify a Label. This attribute will be shadowed by the label DOM attribute on option and command elements.

The title attribute must return the command's Hint, or null if the element does not define a command or does not specify a Hint. This attribute will be shadowed by the title DOM attribute on the HTMLElement interface.

The icon attribute must return the absolute URL of the command's Icon. If the element does not specify an icon, or if the element does not define a command, then the attribute must return null. This attribute will be shadowed by the icon DOM attribute on command elements.

The hidden attribute must return true if the command's Hidden State is that the command is hidden, and false if it is that the command is not hidden. If the element does not define a command, the attribute must return false. This attribute will be shadowed by the hidden DOM attribute on the HTMLElement interface.

The disabled attribute must return true if the command's Disabled State is that the command is disabled, and false if the command is not disabled. This attribute is not affected by the command's Hidden State. If the element does not define a command, the attribute must return false. This attribute will be shadowed by the disabled attribute on button, input, option, and command elements.

The checked attribute must return true if the command's Checked State is that the command is checked, and false if it is that the command is not checked. If the element does not define a command, the attribute must return false. This attribute will be shadowed by the checked attribute on input and command elements.

The click() method must trigger the Action for the command. If the element does not define a command, this method must do nothing. This method will be shadowed by the click() method on HTML elements, and is included only for completeness.

The commands attribute of the document's HTMLDocument interface must return an HTMLCollection rooted at the Document node, whose filter matches only elements that define commands and have IDs.

The following elements can define commands: a, button, input, option, command, bb.

4.11.6.1 Using the a element to define a command

An a element with an href attribute defines a command.

The Type of the command is "command".

The ID of the command is the value of the id attribute of the element, if the attribute is present and not empty. Otherwise the command is an anonymous command.

The Label of the command is the string given by the element's textContent DOM attribute.

The Hint of the command is the value of the title attribute of the element. If the attribute is not present, the Hint is the empty string.

The Icon of the command is the absolute URL obtained from resolving the value of the src attribute of the first img element descendant of the element, relative to that element, if there is such an element and resolving its attribute is successful. Otherwise, there is no Icon for the command.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State facet of the command is always false. (The command is always enabled.)

The Checked State of the command is always false. (The command is never checked.)

The Action of the command is to fire a click event at the element.

4.11.6.2 Using the button element to define a command

A button element always defines a command.

The Type, ID, Label, Hint, Icon, Hidden State, Checked State, and Action facets of the command are determined as for a elements (see the previous section).

The Disabled State of the command mirrors the disabled state of the button.

4.11.6.3 Using the input element to define a command

An input element whose type attribute is in one of the Submit Button, Reset Button, Button, Radio Button, or Checkbox states defines a command.

The Type of the command is "radio" if the type attribute is in the Radio Button state, "checkbox" if the type attribute is in the Checkbox state, and "command" otherwise.

The ID of the command is the value of the id attribute of the element, if the attribute is present and not empty. Otherwise the command is an anonymous command.

The Label of the command depends on the Type of the command:

If the Type is "command", then it is the string given by the value attribute, if any, and a UA-dependent value that the UA uses to label the button itself if the attribute is absent.

Otherwise, the Type is "radio" or "checkbox". If the element is a labeled control, the textContent of the first label element in tree order whose labeled control is the element in question is the Label (in DOM terms, this the string given by element.labels[0].textContent). Otherwise, the value of the value attribute, if present, is the Label. Otherwise, the Label is the empty string.

The Hint of the command is the value of the title attribute of the input element. If the attribute is not present, the Hint is the empty string.

There is no Icon for the command.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State of the command mirrors the disabled state of the control.

The Checked State of the command is true if the command is of Type "radio" or "checkbox" and the element is checked attribute, and false otherwise.

The Action of the command is to fire a click event at the element.

4.11.6.4 Using the option element to define a command

An option element with an ancestor select element and either no value attribute or a value attribute that is not the empty string defines a command.

The Type of the command is "radio" if the option's nearest ancestor select element has no multiple attribute, and "checkbox" if it does.

The ID of the command is the value of the id attribute of the element, if the attribute is present and not empty. Otherwise the command is an anonymous command.

The Label of the command is the value of the option element's label attribute, if there is one, or the value of the option element's textContent DOM attribute if there isn't.

The Hint of the command is the string given by the element's title attribute, if any, and the empty string if the attribute is absent.

There is no Icon for the command.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State of the command is true (disabled) if the element is disabled or if its nearest ancestor select element is disabled, and false otherwise.

The Checked State of the command is true (checked) if the element's selectedness is true, and false otherwise.

The Action of the command depends on its Type. If the command is of Type "radio" then it must pick the option element. Otherwise, it must toggle the option element.

4.11.6.5 Using the command element to define a command

A command element defines a command.

The Type of the command is "radio" if the command's type attribute is "radio", "checkbox" if the attribute's value is "checkbox", and "command" otherwise.

The ID of the command is the value of the id attribute of the element, if the attribute is present and not empty. Otherwise the command is an anonymous command.

The Label of the command is the value of the element's label attribute, if there is one, or the empty string if it doesn't.

The Hint of the command is the string given by the element's title attribute, if any, and the empty string if the attribute is absent.

The Icon for the command is the absolute URL obtained from resolving the value of the element's icon attribute, relative to the element, if it has such an attribute and resolving it is successful. Otherwise, there is no Icon for the command.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State of the command is true (disabled) if the element has a disabled attribute, and false otherwise.

The Checked State of the command is true (checked) if the element has a checked attribute, and false otherwise.

The Action of the command is to invoke the behavior described in the definition of the click() method of the HTMLCommandElement interface.

4.11.6.6 Using the bb element to define a command

A bb element always defines a command.

The Type of the command is "command".

The ID of the command is the value of the id attribute of the element, if the attribute is present and not empty. Otherwise the command is an anonymous command.

The Label of the command is the string given by the element's textContent DOM attribute, if that is not the empty string, or a user-agent-defined string appropriate for the bb element's type attribute's state.

The Hint of the command is the value of the title attribute of the element. If the attribute is not present, the Hint is a user-agent-defined string appropriate for the bb element's type attribute's state.

The Icon of the command is the absolute URL obtained from resolving the value of the src attribute of the first img element descendant of the element, relative to that element, if there is such an element and resolving its attribute is successful. Otherwise, the Icon is a user-agent-defined image appropriate for the bb element's type attribute's state.

The Hidden State facet of the command is true (hidden) if the bb element's type attribute's state is null or if the element has a hidden attribute, and false otherwise.

The Disabled State facet of the command is true if the bb element's type attribute's state's relevance is false, and true otherwise.

The Checked State of the command is always false. (The command is never checked.)

The Action of the command is to perform the action of the bb element's type attribute's state.

4.12 Miscellaneous elements

4.12.1 The legend element

Categories
None.
Contexts in which this element may be used:
As the first child of a fieldset element.
As the first child of a details element.
As a child of a figure element, if there are no other legend element children of that element.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
interface HTMLLegendElement : HTMLElement {
  readonly attribute HTMLFormElement form;
};

The legend element represents a title or explanatory caption for the rest of the contents of the legend element's parent element.

legend . form

Returns the element's form element, if any, or null otherwise.

The form DOM attribute's behavior depends on whether the legend element is in a fieldset element or not. If the legend has a fieldset element as its parent, then the form DOM attribute must return the same value as the form DOM attribute on that fieldset element. Otherwise, it must return null.

4.12.2 The div element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The div element has no special meaning at all. It represents its children. It can be used with the class, lang/xml:lang, and title attributes to mark up semantics common to a group of consecutive elements.

Allowing div elements to contain phrasing content makes it easy for authors to abuse div, using it with the class="" attribute to the point of not having any other elements in the markup. This is a disaster from an accessibility point of view, and it would be nice if we could somehow make such pages non-compliant without preventing people from using divs as the extension mechanism that they are, to handle things the spec can't otherwise do (like making new widgets).

4.13 Matching HTML elements using selectors

There are a number of dynamic selectors that can be used with HTML. This section defines when these selectors match HTML elements.

:link
:visited

All a elements that have an href attribute, all area elements that have an href attribute, and all link elements that have an href attribute, must match one of :link and :visited.

:active

The :active pseudo-class must match the following elements between the time the user begins to activate the element and the time the users stops activating the element:

For example, if the user is using a keyboard to push a button element by pressing the space bar, the element would match this pseudo-class in between the time that the element received the keydown event and the time the element received the keyup event.

:enabled

The :enabled pseudo-class must match the following elements:

:disabled

The :disabled pseudo-class must match the following elements:

:checked

The :checked pseudo-class must match the following elements:

:indeterminate

The :indeterminate pseudo-class must match input elements whose type attribute is in the Checkbox state and whose indeterminate DOM attribute is set to true.

:default

The :default pseudo-class must match the following elements:

:valid

The :valid pseudo-class must match all elements that are candidates for constraint validation and that satisfy their constraints.

:invalid

The :invalid pseudo-class must match all elements that are candidates for constraint validation but that do not satisfy their constraints.

:in-range

The :in-range pseudo-class must match all elements that are candidates for constraint validation and that are neither suffering from an underflow nor suffering from an overflow.

:out-of-range

The :out-of-range pseudo-class must match all elements that are candidates for constraint validation and that are suffering from an underflow or suffering from an overflow.

:required

The :required pseudo-class must match the following elements:

:optional

The :optional pseudo-class must match the following elements:

:read-only
:read-write

The :read-write pseudo-class must match the following elements:

The :read-only pseudo-class must match all other HTML elements.

Another section of this specification defines the target element used with the :target pseudo-class.

This specification does not define when an element matches the :hover, :focus, or :lang() dynamic pseudo-classes, as those are all defined in sufficient detail in a language-agnostic fashion in the Selectors specification. [SELECTORS]

5 Web browsers

This section describes features that apply most directly to Web browsers. Having said that, unless specified elsewhere, the requirements defined in this section do apply to all user agents, whether they are Web browsers or not.

5.1 Browsing contexts

A browsing context is an environment in which Document objects are presented to the user.

A tab or window in a Web browser typically contains a browsing context, as does an iframe or frames in a frameset.

Each browsing context has a corresponding WindowProxy object.

The collection of Documents is the browsing context's session history. At any time, one Document in each browsing context is designated the active document.

Each Document has a collection of one or more views.

A view is a user agent interface tied to a particular media used for the presentation of a particular Document object in some media. A view may be interactive. Each view is represented by an AbstractView object. [DOM2VIEWS]

The main view through which a user primarily interacts with a user agent is the default view. The AbstractView object that represents this view must also implement the Window interface, and is referred to as the Document's Window object. WindowProxy objects forward everything to the active document's default view's Window object.

The defaultView attribute on the Document object's DocumentView interface must return the browsing context's WindowProxy object, not the actual AbstractView object of the default view. [DOM3VIEWS]

The document attribute of an AbstractView object representing a view gives the view's corresponding Document object. [DOM2VIEWS]

Events that use the UIEvent interface are related to a specific view (the view in which the event happened); when that view is the default view, the event object's view attribute's must return the WindowProxy object of the browsing context of that view, not the actual AbstractView object of the default view. [DOM3EVENTS]

A typical Web browser has one obvious view per Document: the browser's window (screen media). This is typically the default view. If a page is printed, however, a second view becomes evident, that of the print media. The two views always share the same underlying Document object, but they have a different presentation of that object. A speech browser might have a different default view, using the speech media.

A Document does not necessarily have a browsing context associated with it. In particular, data mining tools are likely to never instantiate browsing contexts.


A browsing context can have a creator browsing context, the browsing context that was responsible for its creation. Unless otherwise specified, a browsing context has no creator browsing context.

If a browsing context A has a creator browsing context, then the Document that was the active document of that creator browsing context at the time A was created is the creator Document.

When a browsing context is first created, it must be created with a single Document in its session history, whose address is about:blank, which is marked as being an HTML document, and whose character encoding is UTF-8. The Document must have a single child html node, which itself has a single child body node. If the browsing context is created specifically to be immediately navigated, then that initial navigation will have replacement enabled.

The origin of the about:blank Document is set when the Document is created. If the new browsing context has a creator browsing context, then the origin of the about:blank Document is the origin of the creator Document. Otherwise, the origin of the about:blank Document is a globally unique identifier assigned when the new browsing context is created.

5.1.1 Nested browsing contexts

Certain elements (for example, iframe elements) can instantiate further browsing contexts. These are called nested browsing contexts. If a browsing context P has an element E in one of its Documents D that nests another browsing context C inside it, then P is said to be the parent browsing context of C, C is said to be a child browsing context of P, C is said to be nested through D, and E is said to be the browsing context container of C.

A browsing context A is said to be an ancestor of a browsing context B if there exists a browsing context A' that is a child browsing context of A and that is itself an ancestor of B, or if there is a browsing context P that is a child browsing context of A and that is the parent browsing context of B.

The browsing context with no parent browsing context is the top-level browsing context of all the browsing contexts nested within it (either directly or indirectly through other nested browsing contexts).

The transitive closure of parent browsing contexts for a nested browsing context gives the list of ancestor browsing contexts.

A Document is said to be fully active when it is the active document of its browsing context, and either its browsing context is a top-level browsing context, or the Document through which that browsing context is nested is itself fully active.

Because they are nested through an element, child browsing contexts are always tied to a specific Document in their parent browsing context. User agents must not allow the user to interact with child browsing contexts of elements that are in Documents that are not themselves fully active.

A nested browsing context can have a seamless browsing context flag set, if it is embedded through an iframe element with a seamless attribute.

window . top

Returns the WindowProxy for the top-level browsing context.

window . parent

Returns the WindowProxy for the parent browsing context.

window . frameElement

Returns the Element for the browsing context container.

Returns null if there isn't one.

Throws a SECURITY_ERR exception in cross-origin situations.

The top DOM attribute on the Window object of a Document in a browsing context b must return the WindowProxy object of its top-level browsing context (which would be its own WindowProxy object if it was a top-level browsing context itself).

The parent DOM attribute on the Window object of a Document in a browsing context b must return the WindowProxy object of the parent browsing context, if there is one (i.e. if b is a child browsing context), or the WindowProxy object of the browsing context b itself, otherwise (i.e. if it is a top-level browsing context).

The frameElement DOM attribute on the Window object of a Document d, on getting, must run the following algorithm:

  1. If d is not a Document in a child browsing context, return null and abort these steps.

  2. If the parent browsing context's active document does not have the same effective script origin as the script that is accessing the frameElement attribute, then throw a SECURITY_ERR exception.

  3. Otherwise, return the browsing context container for b.

5.1.2 Auxiliary browsing contexts

It is possible to create new browsing contexts that are related to a top level browsing context without being nested through an element. Such browsing contexts are called auxiliary browsing contexts. Auxiliary browsing contexts are always top-level browsing contexts.

An auxiliary browsing context has an opener browsing context, which is the browsing context from which the auxiliary browsing context was created, and it has a furthest ancestor browsing context, which is the top-level browsing context of the opener browsing context when the auxiliary browsing context was created.

The opener DOM attribute on the Window object must return the WindowProxy object of the browsing context from which the current browsing context was created (its opener browsing context), if there is one and it is still available.

5.1.3 Secondary browsing contexts

User agents may support secondary browsing contexts, which are browsing contexts that form part of the user agent's interface, apart from the main content area.

5.1.4 Security

A browsing context A is allowed to navigate a second browsing context B if one of the following conditions is true:

5.1.5 Groupings of browsing contexts

Each browsing context is defined as having a list of zero or more directly reachable browsing contexts. These are:

The transitive closure of all the browsing contexts that are directly reachable browsing contexts forms a unit of related browsing contexts.

Each unit of related browsing contexts is then further divided into the smallest number of groups such that every member of each group has an effective script origin that, through appropriate manipulation of the document.domain attribute, could be made to be the same as other members of the group, but could not be made the same as members of any other group. Each such group is a unit of related similar-origin browsing contexts.

Each unit of related similar-origin browsing contexts can have a first script which is used to obtain, amongst other things, the script's base URL to resolve relative URLs used in scripts running in that unit of related similar-origin browsing contexts. Initially, there is no first script.

5.1.6 Browsing context names

Browsing contexts can have a browsing context name. By default, a browsing context has no name (its name is not set).

A valid browsing context name is any string with at least one character that does not start with a U+005F LOW LINE character. (Names starting with an underscore are reserved for special keywords.)

A valid browsing context name or keyword is any string that is either a valid browsing context name or that is an ASCII case-insensitive match for one of: _blank, _self, _parent, or _top.

The rules for choosing a browsing context given a browsing context name are as follows. The rules assume that they are being applied in the context of a browsing context.

  1. If the given browsing context name is the empty string or _self, then the chosen browsing context must be the current one.

  2. If the given browsing context name is _parent, then the chosen browsing context must be the parent browsing context of the current one, unless there isn't one, in which case the chosen browsing context must be the current browsing context.

  3. If the given browsing context name is _top, then the chosen browsing context must be the most top-level browsing context of the current one.

  4. If the given browsing context name is not _blank and there exists a browsing context whose name is the same as the given browsing context name, and the current browsing context is allowed to navigate that browsing context, and the user agent determines that the two browsing contexts are related enough that it is ok if they reach each other, then that browsing context must be the chosen one. If there are multiple matching browsing contexts, the user agent should select one in some arbitrary consistent manner, such as the most recently opened, most recently focused, or more closely related.

  5. Otherwise, a new browsing context is being requested, and what happens depends on the user agent's configuration and/or abilities:

    If the current browsing context has the sandboxed navigation browsing context flag set.
    The user agent may offer to create a new top-level browsing context or reuse an existing top-level browsing context. If the user picks one of those options, then the designated browsing context must be the chosen one (the browsing context's name isn't set to the given browsing context name). Otherwise (if the user agent doesn't offer the option to the user, or if the user declines to allow a browsing context to be used) there must not be a chosen browsing context.
    If the user agent has been configured such that in this instance it will create a new browsing context, and the browsing context is being requested as part of following a hyperlink whose link types include the noreferrer keyword
    A new top-level browsing context must be created. If the given browsing context name is not _blank, then the new top-level browsing context's name must be the given browsing context name (otherwise, it has no name). The chosen browsing context must be this new browsing context. If it is immediately navigated, then the navigation will be done with replacement enabled.
    If the user agent has been configured such that in this instance it will create a new browsing context, and the noreferrer keyword doesn't apply
    A new auxiliary browsing context must be created, with the opener browsing context being the current one. If the given browsing context name is not _blank, then the new auxiliary browsing context's name must be the given browsing context name (otherwise, it has no name). The chosen browsing context must be this new browsing context. If it is immediately navigated, then the navigation will be done with replacement enabled.
    If the user agent has been configured such that in this instance it will reuse the current browsing context
    The chosen browsing context is the current browsing context.
    If the user agent has been configured such that in this instance it will not find a browsing context
    There must not be a chosen browsing context.

    User agent implementors are encouraged to provide a way for users to configure the user agent to always reuse the current browsing context.

5.2 The WindowProxy object

As mentioned earlier, each browsing context has a WindowProxy object. This object is unusual in that it must proxy all operations to the Window object of the browsing context's active document. It is thus indistinguishable from that Window object in every way, except that it is not equal to it.

5.3 The Window object

[IndexGetter, NameGetter=OverrideBuiltins]
interface Window {
  // the current browsing context
  readonly attribute WindowProxy window;
  readonly attribute WindowProxy self;
           attribute DOMString name;
  [PutForwards=href] readonly attribute Location location;
  readonly attribute History history;
  readonly attribute UndoManager undoManager;
  Selection getSelection();
  [Replaceable] readonly attribute BarProp locationbar;
  [Replaceable] readonly attribute BarProp menubar;
  [Replaceable] readonly attribute BarProp personalbar;
  [Replaceable] readonly attribute BarProp scrollbars;
  [Replaceable] readonly attribute BarProp statusbar;
  [Replaceable] readonly attribute BarProp toolbar;
  void close();
  void focus();
  void blur();

  // other browsing contexts
  readonly attribute WindowProxy frames;
  readonly attribute unsigned long length;
  readonly attribute WindowProxy top;
  [Replaceable] readonly attribute WindowProxy opener;
  readonly attribute WindowProxy parent;
  readonly attribute Element frameElement;
  WindowProxy open([Optional] in DOMString url, [Optional] in DOMString target, [Optional] in DOMString features, [Optional] in DOMString replace);

  // the user agent
  readonly attribute Navigator navigator; 
  readonly attribute Storage localStorage; 
  readonly attribute Storage sessionStorage;
  Database openDatabase(in DOMString name, in DOMString version, in DOMString displayName, in unsigned long estimatedSize);
  readonly attribute ApplicationCache applicationCache;

  // user prompts
  void alert(in DOMString message);
  boolean confirm(in DOMString message);
  DOMString prompt(in DOMString message, [Optional] in DOMString default);
  void print();
  any showModalDialog(in DOMString url, [Optional] in any argument);

  // cross-document messaging
  void postMessage(in any message, in DOMString targetOrigin);
  void postMessage(in any message, in MessagePortArray ports, in DOMString targetOrigin);

  // event handler DOM attributes
           attribute Function onabort;
           attribute Function onafterprint;
           attribute Function onbeforeprint;
           attribute Function onbeforeunload;
           attribute Function onblur;
           attribute Function oncanplay;
           attribute Function oncanplaythrough;
           attribute Function onchange;
           attribute Function onclick;
           attribute Function oncontextmenu;
           attribute Function ondataunavailable;
           attribute Function ondblclick;
           attribute Function ondrag;
           attribute Function ondragend;
           attribute Function ondragenter;
           attribute Function ondragleave;
           attribute Function ondragover;
           attribute Function ondragstart;
           attribute Function ondrop;
           attribute Function ondurationchange;
           attribute Function onemptied;
           attribute Function onended;
           attribute Function onerror;
           attribute Function onfocus;
           attribute Function onformchange;
           attribute Function onforminput;
           attribute Function onhashchange;
           attribute Function oninput;
           attribute Function oninvalid;
           attribute Function onkeydown;
           attribute Function onkeypress;
           attribute Function onkeyup;
           attribute Function onload;
           attribute Function onloadeddata;
           attribute Function onloadedmetadata;
           attribute Function onloadstart;
           attribute Function onmessage;
           attribute Function onmousedown;
           attribute Function onmousemove;
           attribute Function onmouseout;
           attribute Function onmouseover;
           attribute Function onmouseup;
           attribute Function onmousewheel;
           attribute Function onoffline;
           attribute Function ononline;
           attribute Function onpause;
           attribute Function onplay;
           attribute Function onplaying;
           attribute Function onpopstate;
           attribute Function onprogress;
           attribute Function onratechange;
           attribute Function onreadystatechange;
           attribute Function onredo;
           attribute Function onresize;
           attribute Function onscroll;
           attribute Function onseeked;
           attribute Function onseeking;
           attribute Function onselect;
           attribute Function onshow;
           attribute Function onstalled;
           attribute Function onstorage;
           attribute Function onsubmit;
           attribute Function onsuspend;
           attribute Function ontimeupdate;
           attribute Function onundo;
           attribute Function onunload;
           attribute Function onvolumechange;
           attribute Function onwaiting;
};
window . window
window . frames
window . self

These attributes all return window.

The Window object must also implement the EventTarget interface.

The window, frames, and self DOM attributes must all return the Window object's browsing context's WindowProxy object.

5.3.1 Security

User agents must raise a SECURITY_ERR exception whenever any of the members of a Window object are accessed by scripts whose effective script origin is not the same as the Window object's Document's effective script origin, with the following exceptions:

User agents must not allow scripts to override the location object's setter.

5.3.2 APIs for creating and navigating browsing contexts by name

window = window . open( [ url [, target [, features [, replace ] ] ] ] )

Opens a window to show url (defaults to about:blank), and returns it. The target argument gives the name of the new window. If a window exists with that name already, it is reused. The replace attribute, if true, means that whatever page is currently open in that window will be removed from the window's session history. The features argument is ignored.

window . name [ = value ]

Returns the name of the window.

Can be set, to change the name.

window . close()

Closes the window.

The open() method on Window objects provides a mechanism for navigating an existing browsing context or opening and navigating an auxiliary browsing context.

The method has four arguments, though they are all optional.

The first argument, url, must be a valid URL for a page to load in the browsing context. If no arguments are provided, or if the first argument is the empty string, then the url argument defaults to "about:blank". The argument must be resolved to an absolute URL (or an error), relative to the first script's base URL, when the method is invoked.

The second argument, target, specifies the name of the browsing context that is to be navigated. It must be a valid browsing context name or keyword. If fewer than two arguments are provided, then the name argument defaults to the value "_blank".

The third argument, features, has no effect and is supported for historical reasons only.

The fourth argument, replace, specifies whether or not the new page will replace the page currently loaded in the browsing context, when target identifies an existing browsing context (as opposed to leaving the current page in the browsing context's session history). When three or fewer arguments are provided, replace defaults to false.

When the method is invoked, the user agent must first select a browsing context to navigate by applying the rules for choosing a browsing context given a browsing context name using the target argument as the name and the browsing context of the script as the context in which the algorithm is executed, unless the user has indicated a preference, in which case the browsing context to navigate may instead be the one indicated by the user.

For example, suppose there is a user agent that supports control-clicking a link to open it in a new tab. If a user clicks in that user agent on an element whose onclick handler uses the window.open() API to open a page in an iframe, but, while doing so, holds the control key down, the user agent could override the selection of the target browsing context to instead target a new tab.

Then, the user agent must navigate the selected browsing context to the absolute URL (or error) obtained from resolving url earlier. If the replace is true, then replacement must be enabled; otherwise, it must not be enabled unless the browsing context was just created as part of the the rules for choosing a browsing context given a browsing context name. The navigation must be done with the browsing context of the script that invoked the method as the source browsing context.

The method must return the WindowProxy object of the browsing context that was navigated, or null if no browsing context was navigated.


The name attribute of the Window object must, on getting, return the current name of the browsing context, and, on setting, set the name of the browsing context to the new value.

The name gets reset when the browsing context is navigated to another domain.


The close() method on Window objects should, if the corresponding browsing context A is an auxiliary browsing context that was created by a script (as opposed to by an action of the user), and if the browsing context of the script that invokes the method is allowed to navigate the browsing context A, close the browsing context A (and may discard it too).

5.3.3 Accessing other browsing contexts

window . length

Returns the number of child browsing contexts.

window[index]

Returns the indicated child browsing context.

The length DOM attribute on the Window interface must return the number of child browsing contexts of the Document.

The indices of the supported indexed properties on the Window object at any instant are the numbers in the range 0 .. n-1, where n is the number of child browsing contexts of the Document. If n is zero then there are no supported indexed properties.

When a Window object is indexed to retrieve an indexed property index, the value returned must be the indexth child browsing context of the Document, sorted in the tree order of the elements nesting those browsing contexts.

These properties are the dynamic nested browsing context properties.

5.3.4 Named access on the Window object

window[name]

Returns the indicated child browsing context.

The Window interface supports named properties. The names of the supported named properties at any moment consist of:

When the Window object is indexed for property retrieval using a name name, then the user agent must return the value obtained using the following steps:

  1. Let elements be the list of named elements with the name name in the active document.

    There will be at least one such element, by definition.

  2. If elements contains an iframe element, then return the WindowProxy object of the nested browsing context represented by the first such iframe element in tree order, and abort these steps.

  3. Otherwise, if elements has only one element, return that element and abort these steps.

  4. Otherwise return an HTMLCollection rooted at the Document node, whose filter matches only named elements with the name name.

Named elements with the name name, for the purposes of the above algorithm, are those that are either:

5.3.5 Garbage collection and browsing contexts

A browsing context has a strong reference to each of its Documents and its WindowProxy object, and the user agent itself has a strong reference to its top-level browsing contexts.

A Document has a strong reference to each of its views and their AbstractView objects.

When a browsing context is to discard a Document, that means that it is to lose the strong reference from the Document's browsing context to the Document, and that any tasks associated with the Document in any task source must be removed without being run.

The browsing context's default view's Window object has a strong reference of its own to its Document object.

When a browsing context is discarded, the strong reference from the user agent itself to the browsing context must be severed, and all the Document objects for all the entries in the browsing context's session history must be discarded as well.

User agents may discard top-level browsing contexts at any time (typically, in response to user requests, e.g. when a user closes a window containing one or more top-level browsing contexts). Other browsing contexts must be discarded once their WindowProxy object is eligible for garbage collection.

5.3.6 Browser interface elements

To allow Web pages to integrate with Web browsers, certain Web browser interface elements are exposed in a limited way to scripts in Web pages.

Each interface element is represented by a BarProp object:

interface BarProp {
           attribute boolean visible;
};
window . locationbar . visible

Returns true if the location bar is visible; otherwise, returns false.

window . menubar . visible

Returns true if the menu bar is visible; otherwise, returns false.

window . personalbar . visible

Returns true if the personal bar is visible; otherwise, returns false.

window . scrollbars . visible

Returns true if the scroll bars are visible; otherwise, returns false.

window . statusbar . visible

Returns true if the status bar is visible; otherwise, returns false.

window . toolbar . visible

Returns true if the tool bar is visible; otherwise, returns false.

The visible attribute, on getting, must return either true or a value determined by the user agent to most accurately represent the visibility state of the user interface element that the object represents, as described below. On setting, the new value must be discarded.

The following BarProp objects exist for each Document object in a browsing context. Some of the user interface elements represented by these objects might have no equivalent in some user agents; for those user agents, unless otherwise specified, the object must act as if it was present and visible (i.e. its visible attribute must return true).

The location bar BarProp object
Represents the user interface element that contains a control that displays the URL of the active document, or some similar interface concept.
The menu bar BarProp object
Represents the user interface element that contains a list of commands in menu form, or some similar interface concept.
The personal bar BarProp object
Represents the user interface element that contains links to the user's favorite pages, or some similar interface concept.
The scrollbar BarProp object
Represents the user interface element that contains a scrolling mechanism, or some similar interface concept.
The status bar BarProp object
Represents a user interface element found immediately below or after the document, as appropriate for the default view's media. If the user agent has no such user interface element, then the object may act as if the corresponding user interface element was absent (i.e. its visible attribute may return false).
The tool bar BarProp object
Represents the user interface element found immediately above or before the document, as appropriate for the default view's media. If the user agent has no such user interface element, then the object may act as if the corresponding user interface element was absent (i.e. its visible attribute may return false).

The locationbar attribute must return the location bar BarProp object.

The menubar attribute must return the menu bar BarProp object.

The personalbar attribute must return the personal bar BarProp object.

The scrollbars attribute must return the scrollbar BarProp object.

The statusbar attribute must return the status bar BarProp object.

The toolbar attribute must return the tool bar BarProp object.

5.4 Origin

The origin of a resource and the effective script origin of a resource are both either opaque identifiers or tuples consisting of a scheme component, a host component, a port component, and optionally extra data.

The extra data could include the certificate of the site when using encrypted connections, to ensure that if the site's secure certificate changes, the origin is considered to change as well.

These characteristics are defined as follows:

For URLs

The origin and effective script origin of the URL is whatever is returned by the following algorithm:

  1. Let url be the URL for which the origin is being determined.

  2. Parse url.

  3. If url does not use a server-based naming authority, or if parsing url failed, or if url is not an absolute URL, then return a new globally unique identifier.

  4. Let scheme be the <scheme> component of url, converted to lowercase.

  5. If the UA doesn't support the protocol given by scheme, then return a new globally unique identifier.

  6. If scheme is "file", then the user agent may return a UA-specific value.

  7. Let host be the <host> component of url.

  8. Apply the IDNA ToASCII algorithm to host, with both the AllowUnassigned and UseSTD3ASCIIRules flags set. Let host be the result of the ToASCII algorithm.

    If ToASCII fails to convert one of the components of the string, e.g. because it is too long or because it contains invalid characters, then return a new globally unique identifier. [RFC3490]

  9. Let host be the result of converting host to lowercase.

  10. If there is no <port> component, then let port be the default port for the protocol given by scheme. Otherwise, let port be the <port> component of url.

  11. Return the tuple (scheme, host, port).

In addition, if the URL is in fact associated with a Document object that was created by parsing the resource obtained from fetching URL, and this was done over a secure connection, then the server's secure certificate may be added to the origin as additional data.

For scripts

The origin and effective script origin of a script are determined from another resource, called the owner:

If a script is in a script element
The owner is the Document to which the script element belongs.
If a script is in an event handler content attribute
The owner is the Document to which the attribute node belongs.
If a script is a function or other code reference created by another script
The owner is the script that created it.
If a script is a javascript: URL that was returned as the location of an HTTP redirect (or equivalent in other protocols)
The owner is the URL that redirected to the javascript: URL.
If a script is a javascript: URL in an attribute
The owner is the Document of the element on which the attribute is found.
If a script is a javascript: URL in a style sheet
The owner is the URL of the style sheet.
If a script is a javascript: URL to which a browsing context is being navigated, the URL having been provided by the user (e.g. by using a bookmarklet)
The owner is the Document of the browsing context's active document.
If a script is a javascript: URL to which a browsing context is being navigated, the URL having been declared in markup
The owner is the Document of the element (e.g. an a or area element) that declared the URL.
If a script is a javascript: URL to which a browsing context is being navigated, the URL having been provided by script
The owner is the script that provided the URL.

The origin of the script is then equal to the origin of the owner, and the effective script origin of the script is equal to the effective script origin of the owner.

For Document objects and images
If a Document is in a browsing context whose sandboxed origin browsing context flag was set when the Document was created
The origin is a globally unique identifier assigned when the Document is created.
If a Document or image was returned by the XMLHttpRequest API
The origin and effective script origin are equal to the origin and effective script origin of the Document object of the Window object from which the XMLHttpRequest constructor was invoked. (That is, they track the Document to which the XMLHttpRequest object's Document pointer pointed when it was created.) [XHR]
If a Document or image was generated from a javascript: URL
The origin is equal to the origin of the script of that javascript: URL.
If a Document or image was served over the network and has an address that uses a URL scheme with a server-based naming authority
The origin is the origin of the address of the Document or the URL of the image, as appropriate.
If a Document or image was generated from a data: URL that was returned as the location of an HTTP redirect (or equivalent in other protocols)
The origin is the origin of the URL that redirected to the data: URL.
If a Document or image was generated from a data: URL found in another Document or in a script
The origin is the origin of the Document or script in which the data: URL was found.
If a Document has the address "about:blank"
The origin of the Document is the origin it was assigned when its browsing context was created.
If a Document or image was obtained in some other manner (e.g. a data: URL typed in by the user, a Document created using the createDocument() API, a data: URL returned as the location of an HTTP redirect, etc)
The origin is a globally unique identifier assigned when the Document or image is created.

When a Document is created, unless stated otherwise above, its effective script origin is initialized to the origin of the Document. However, the document.domain attribute can be used to change it.

The Unicode serialization of an origin is the string obtained by applying the following algorithm to the given origin:

  1. If the origin in question is not a scheme/host/port tuple, then return the literal string "null" and abort these steps.

  2. Otherwise, let result be the scheme part of the origin tuple.

  3. Append the string "://" to result.

  4. Apply the IDNA ToUnicode algorithm to each component of the host part of the origin tuple, and append the results — each component, in the same order, separated by U+002E FULL STOP characters (".") — to result.

  5. If the port part of the origin tuple gives a port that is different from the default port for the protocol given by the scheme part of the origin tuple, then append a U+003A COLON character (":") and the given port, in base ten, to result.

  6. Return result.

The ASCII serialization of an origin is the string obtained by applying the following algorithm to the given origin:

  1. If the origin in question is not a scheme/host/port tuple, then return the literal string "null" and abort these steps.

  2. Otherwise, let result be the scheme part of the origin tuple.

  3. Append the string "://" to result.

  4. Apply the IDNA ToASCII algorithm the host part of the origin tuple, with both the AllowUnassigned and UseSTD3ASCIIRules flags set, and append the results result.

    If ToASCII fails to convert one of the components of the string, e.g. because it is too long or because it contains invalid characters, then return the empty string and abort these steps. [RFC3490]

  5. If the port part of the origin tuple gives a port that is different from the default port for the protocol given by the scheme part of the origin tuple, then append a U+003A COLON character (":") and the given port, in base ten, to result.

  6. Return result.

Two origins are said to be the same origin if the following algorithm returns true:

  1. Let A be the first origin being compared, and B be the second origin being compared.

  2. If A and B are both opaque identifiers, and their value is equal, then return true.

  3. Otherwise, if either A or B or both are opaque identifiers, return false.

  4. If A and B have scheme components that are not identical, return false.

  5. If A and B have host components that are not identical, return false.

  6. If A and B have port components that are not identical, return false.

  7. If either A or B have additional data, but that data is not identical for both, return false.

  8. Return true.

5.4.1 Relaxing the same-origin restriction

document . domain [ = domain ]

Returns the current domain used for security checks.

Can be set to a value that removes subdomains, to allow pages on other subdomains of the same domain (if they do the same thing) to access each other.

The domain attribute on Document objects must be initialized to the document's domain, if it has one, and the empty string otherwise. If the value is an IPv6 address, then the square brackets from the host portion of the <host> component must be omitted from the attribute's value.

On getting, the attribute must return its current value, unless the document was created by XMLHttpRequest, in which case it must throw an INVALID_ACCESS_ERR exception.

On setting, the user agent must run the following algorithm:

  1. If the document was created by XMLHttpRequest, throw an INVALID_ACCESS_ERR exception and abort these steps.

  2. If the new value is an IP address, let new value be the new value. Otherwise, apply the IDNA ToASCII algorithm to the new value, with both the AllowUnassigned and UseSTD3ASCIIRules flags set, and let new value be the result of the ToASCII algorithm.

    If ToASCII fails to convert one of the components of the string, e.g. because it is too long or because it contains invalid characters, then throw a SECURITY_ERR exception and abort these steps. [RFC3490]

  3. If new value is not exactly equal to the current value of the document.domain attribute, then run these substeps:

    1. If the current value is an IP address, throw a SECURITY_ERR exception and abort these steps.

    2. If new value, prefixed by a U+002E FULL STOP ("."), does not exactly match the end of the current value, throw a SECURITY_ERR exception and abort these steps.

    3. If new value matches a suffix in the Public Suffix List, or, if new value, prefixed by a U+002E FULL STOP ("."), matches the end of a suffix in the Public Suffix List, then throw a SECURITY_ERR exception and abort these steps. [PSL]

      Suffixes must be compared after applying the IDNA ToASCII algorithm to them, with both the AllowUnassigned and UseSTD3ASCIIRules flags set, in an ASCII case-insensitive manner. [RFC3490]

  4. Set the attribute's value to new value.

  5. Set the host part of the effective script origin tuple of the Document to new value.

  6. Set the port part of the effective script origin tuple of the Document to "manual override" (a value that, for the purposes of comparing origins, is identical to "manual override" but not identical to any other value).

The domain of a Document is the host part of the document's origin, if that is a scheme/host/port tuple. If it isn't, then the document does not have a domain.

The domain attribute is used to enable pages on different hosts of a domain to access each others' DOMs.

5.5 Scripting

5.5.1 Introduction

Various mechanisms can cause author-provided executable code to run in the context of a document. These mechanisms include, but are probably not limited to:

5.5.2 Enabling and disabling scripting

Scripting is enabled in a browsing context when all of the following conditions are true:

Scripting is disabled in a browsing context when any of the above conditions are false (i.e. when scripting is not enabled).


Scripting is enabled for a node if the Document object of the node (the node itself, if it is itself a Document object) has an associated browsing context, and scripting is enabled in that browsing context.

Scripting is disabled for a node if there is no such browsing context, or if scripting is disabled in that browsing context.

5.5.3 Processing model

5.5.3.1 Definitions

A script has:

A script execution environment

The characteristics of the script execution environment depend on the language, and are not defined by this specification.

In JavaScript, the script execution environment consists of the interpreter, the stack of execution contexts, the global code and function code and the Function objects resulting, and so forth.

A list of code entry-points

Each code entry-point represents a block of executable code that the script exposes to other scripts and to the user agent.

Each Function object in a JavaScript script execution environment has a corresponding code entry-point, for instance.

The main program code of the script, if any, is the initial code entry-point. Typically, the code corresponding to this entry-point is executed immediately after the script is parsed.

In JavaScript, this corresponds to the execution context of the global code.

A relationship with the script's global object

An object that provides the APIs that the code can use.

This is typically a Window object. In JavaScript, this corresponds to the global object.

When a script's global object is an empty object, it can't do anything that interacts with the environment.

If the script's global object is a Window object, then in JavaScript, the this keyword in the global scope must return the Window object's WindowProxy object.

This is a willful violation of the JavaScript specification current at the time of writing (ECMAScript edition 3). [ECMA262]

A relationship with the script's browsing context

A browsing context that is assigned responsibility for actions taken by the script.

When a script creates and navigates a new top-level browsing context, the opener attribute of the new browsing context's Window object will be set to the script's browsing context's WindowProxy object.

A URL character encoding

A character encoding, set when the script is created, used to encode URLs. If the character encoding is set from another source, e.g. a document's character encoding, then the script's URL character encoding must follow the source, so that if the source's changes, so does the script's.

A base URL

A URL, set when the script is created, used to resolve relative URLs. If the base URL is set from another source, e.g. a document base URL, then the script's base URL must follow the source, so that if the source's changes, so does the script's.

5.5.3.2 Calling scripts

When a user agent is to jump to a code entry-point for a script, for example to invoke an event listener defined in that script, the user agent must run the following steps:

  1. If the script's global object is a Window object whose Document object is not fully active, then abort these steps without doing anything. The callback is not fired.

  2. Set the first script to be the script being invoked.

  3. Make the script execution environment for the script execute the code for the given code entry-point.

  4. Set the first script back to whatever it was when this algorithm started.

This algorithm is not invoked by one script calling another.

5.5.3.3 Creating scripts

When the specification says that a script is to be created, given some script source, its scripting language, a global object, a browsing context, a character encoding, and a base URL, the user agent must run the following steps:

  1. If scripting is disabled for browsing context passed to this algorithm, then abort these steps, as if the script did nothing but return void.

  2. Set up a script execution environment as appropriate for the scripting language.

  3. Parse/compile/initialize the source of the script using the script execution environment, as appropriate for the scripting language, and thus obtain the list of code entry-points for the script. If the semantics of the scripting language and the given source code are such that there is executable code to be immediately run, then the initial code entry-point is the entry-point for that code.

  4. Set up the script's global object, the script's browsing context, the script's URL character encoding, and the script's base URL from the settings passed to this algorithm.

  5. Jump to the script's initial code entry-point.


When the user agent is to create an impotent script, given some script source, its scripting language, and a browsing context, the user agent must create a script, using the given script source and scripting language, using a new empty object as the global object, and using the given browsing context as the browsing context. The character encoding and base URL for the resulting script are not important as no APIs are exposed to the script.


When the specification says that a script is to be created from a node node, given some script source and its scripting language, the user agent must create a script, using the given script source and scripting language, and using the script settings determined from the node node.

The script settings determined from the node node are computed as follows:

  1. Let document be the Document of node (or node itself if it is a Document).

  2. The browsing context is the browsing context of document.

  3. The global object is the Window object of document.

  4. The character encoding is the character encoding of document. (This is a reference, not a copy.)

  5. The base URL is the base URL of document. (This is a reference, not a copy.)

5.5.3.4 Killing scripts

User agents may impose resource limitations on scripts, for example CPU quotas, memory limits, total execution time limits, or bandwidth limitations. When a script exceeds a limit, the user agent may either throw a QUOTA_EXCEEDED_ERR exception, abort the script without an exception, prompt the user, or throttle script execution.

For example, the following script never terminates. A user agent could, after waiting for a few seconds, prompt the user to either terminate the script or let it continue.

<script>
 while (true) { /* loop */ }
</script>

User agents are encouraged to allow users to disable scripting whenever the user is prompted either by a script (e.g. using the window.alert() API) or because of a script's actions (e.g. because it has exceeded a time limit).

If scripting is disabled while a script is executing, the script should be terminated immediately.

5.5.4 Event loops

5.5.4.1 Definitions

To coordinate events, user interaction, scripts, rendering, networking, and so forth, user agents must use event loops as described in this section.

There must be at least one event loop per user agent, and at most one event loop per unit of related similar-origin browsing contexts.

An event loop always has at least one browsing context. If an event loop's browsing contexts all go away, then the event loop goes away as well. A browsing context always has an event loop coordinating its activities.

Other specifications can define new kinds of event loops that aren't associated with browsing contexts.

An event loop has one or more task queues. A task queue is an ordered list of tasks, which can be:

Events

Asynchronously dispatching an Event object at a particular EventTarget object is a task.

Not all events are dispatched using the task queue, many are dispatched synchronously during other tasks.

Parsing

The HTML parser tokenizing a single byte, and then processing any resulting tokens, is a task.

Callbacks

Calling a callback asynchronously is a task.

Using a resource

When an algorithm fetches a resource, if the fetching occurs asynchronously then the processing of the resource once some or all of the resource is available is a task.

Reacting to DOM manipulation

Some elements have tasks that trigger in response to DOM manipulation, e.g. when that element is inserted into the document.

Each task is associated with a Document; if the task was queued in the context of an element, then it is the element's Document; if the task was queued in the context of a browsing context, then it is the browsing context's active document at the time the task was queued; if the task was queued by or for a script then the document is the script's browsing context's active document at the time the task was queued.

When a user agent is to queue a task, it must add the given task to one of the task queues of the relevant event loop. All the tasks from one particular task source (e.g. the callbacks generated by timers, the events dispatched for mouse movements, the tasks queued for the parser) must always be added to the same task queue, but tasks from different task sources may be placed in different task queues.

For example, a user agent could have one task queue for mouse and key events (the user interaction task source), and another for everything else. The user agent could then give keyboard and mouse events preference over other tasks three quarters of the time, keeping the interface responsive but not starving other task queues, and never processing events from any one task source out of order.

A user agent is required to have one storage mutex. This mutex is used to control access to shared state like cookies. At any one point, the storage mutex is either free, or owned by a particular event loop or instance of the fetching algorithm.

Whenever a script calls into a plugin, and whenever a plugin calls into a script, the user agent must release the storage mutex.

5.5.4.2 Processing model

An event loop must continually run through the following steps for as long as it exists:

  1. Run the oldest task on one of the event loop's task queues, ignoring tasks whose associated Documents are not fully active. The user agent may pick any task queue.

  2. If the storage mutex is now owned by the event loop, release it so that it is once again free.

  3. Remove that task from its task queue.

  4. If necessary, update the rendering or user interface of any Document or browsing context to reflect the current state.

  5. Return to the first step of the event loop.


Some of the algorithms in this specification, for historical reasons, require the user agent to pause while running a task until some condition has been met. While a user agent has a paused task, the corresponding event loop must not run further tasks, and any script in the currently running task must block. User agents should remain responsive to user input while paused, however, albeit in a reduced capacity since the event loop will not be doing anything.


When a user agent is to obtain the storage mutex as part of running a task, it must run through the following steps:

  1. If the storage mutex is already owned by this task's event loop, then abort these steps.

  2. Otherwise, pause until the storage mutex can be taken by the event loop.

  3. Take ownership of the storage mutex.

5.5.4.3 Generic task sources

The following task sources are used by a number of mostly unrelated features in this and other specifications.

The DOM manipulation task source

This task source is used for features that react to DOM manipulations, such as things that happen asynchronously when an element is inserted into the document.

The user interaction task source

This task source is used for features that react to user interaction, for example keyboard or mouse input.

Asynchronous events sent in response to user input (e.g. click events) must be dispatched using tasks queued with the user interaction task source. [DOMEVENTS]

The networking task source

This task source is used for features that trigger in response to network activity.

5.5.5 The javascript: protocol

When a URL using the javascript: protocol is dereferenced, the user agent must run the following steps:

  1. Let the script source be the string obtained using the content retrieval operation defined for javascript: URLs. [JSURL]

  2. Use the appropriate step from the following list:

    If a browsing context is being navigated to a javascript: URL, and the active document of that browsing context has the same origin as the script given by that URL

    Let address be the address of the active document of the browsing context being navigated.

    If address is about:blank, and the browsing context being navigated has a creator browsing context, then let address be the address of the creator Document instead.

    Create a script from the Document node of the active document, using the aforementioned script source, and assuming the scripting language is JavaScript.

    Let result be the return value of the initial code entry-point of this script. If an exception was raised, let result be void instead. (The result will be void also if scripting is disabled.)

    When it comes time to set the document's address in the navigation algorithm, use address as the override URL.

    If the Document object of the element, attribute, or style sheet from which the javascript: URL was reached has an associated browsing context

    Create an impotent script using the aforementioned script source, with the scripting language set to JavaScript, and with the Document's object's browsing context as the browsing context.

    Let result be the return value of the initial code entry-point of this script. If an exception was raised, let result be void instead. (The result will be void also if scripting is disabled.)

    Otherwise

    Let result be void.

  3. If the result of executing the script is void (there is no return value), then the URL must be treated in a manner equivalent to an HTTP resource with an HTTP 204 No Content response.

    Otherwise, the URL must be treated in a manner equivalent to an HTTP resource with a 200 OK response whose Content-Type metadata is text/html and whose response body is the return value converted to a string value.

    Certain contexts, in particular img elements, ignore the Content-Type metadata.

So for example a javascript: URL for a src attribute of an img element would be evaluated in the context of an empty object as soon as the attribute is set; it would then be sniffed to determine the image type and decoded as an image.

A javascript: URL in an href attribute of an a element would only be evaluated when the link was followed.

The src attribute of an iframe element would be evaluated in the context of the iframe's own browsing context; once evaluated, its return value (if it was not void) would replace that browsing context's document, thus changing the variables visible in that browsing context.

5.5.6 Events

5.5.6.1 Event handler attributes

Many objects can have event handler attributes specified. These act as bubbling event listeners for the element on which they are specified.

An event handler attribute, unless otherwise specified, can either have the value null or be set to a Function object. Initially, an event handler attribute must be set to null.

Event handler attributes are exposed in one or two ways.

The first way, common to all event handler attributes, is as an event handler DOM attribute.

The second way is as an event handler content attribute. Event handlers on HTML elements and some of the event handlers on Window objects are exposed in this way.


Event handler DOM attributes, on setting, must set the corresponding event handler attribute to their new value, and on getting, must return whatever the current value of the corresponding event handler attribute is (possibly null).

Certain event handler DOM attributes have additional requirements, in particular the onmessage attribute of MessagePort objects.


Event handler content attributes, when specified, must contain valid JavaScript code matching the FunctionBody production. [ECMA262]

When an event handler content attribute is set, if the element is owned by a Document that is in a browsing context, and scripting is enabled for that browsing context, the user agent must run the following steps to create a script after setting the content attribute to its new value:

  1. Set up a script execution environment for JavaScript.

  2. Using this script execution environment, interpret the attribute's new value as the body of an anonymous function, with the function's arguments set as follows:

    If the attribute is the onerror attribute of the Window object
    Let the function have three arguments, named event, source, and fileno.
    Otherwise
    Let the function have a single argument called event.

    Link the new function's scope chain from the activation object of the handler, to the element's object, to the element's form owner, if it has one, to the element's Document object, to the Window object of that Document. Set the function's this parameter to the Element object representing the element. Let this function be the only entry in the script's list of code entry-points.

    See ECMA262 Edition 3, sections 10.1.6 and 10.2.3, for more details on activation objects. [ECMA262]

  3. If the previous steps failed to compile the script, then set the corresponding event handler attribute to null and abort these steps.

  4. Set up the script's global object, the script's browsing context, the script's URL character encoding, and the script's base URL from the script settings determined from the node on which the attribute is being set.

  5. Set the corresponding event handler attribute to the aforementioned function.

When an event handler content attribute is set on an element owned by a Document that is not in a browsing context, the corresponding event handler attribute is not changed.

Removing an event handler content attribute does not reset the corresponding event handler attribute.

How do we allow non-JS event handlers?


All event handler attributes on an element, whether set to null or to a Function object, must be registered as event listeners on the element, as if the addEventListenerNS() method on the Element object's EventTarget interface had been invoked when the event handler attribute's element or object was created, with the event type (type argument) equal to the type corresponding to the event handler attribute (the event handler event type), the namespace (namespaceURI argument) set to null, the listener set to be a target and bubbling phase listener (useCapture argument set to false), the event group set to the default group (evtGroup argument set to null), and the event listener itself (listener argument) set to do nothing while the event handler attribute's value is not a Function object, and set to invoke the call() callback of the Function object associated with the event handler attribute otherwise.

The listener argument is emphatically not the event handler attribute itself.

The interfaces implemented by the event object do not affect whether an event handler attribute is used or not.

When an event handler attribute's Function object is invoked, its call() callback must be invoked with one argument, set to the Event object of the event in question.

The handler's return value must then be processed as follows:

If the event type is mouseover

If the return value is a boolean with the value true, then the event must be canceled.

If the event object is a BeforeUnloadEvent object

If the return value is a string, and the event object's returnValue attribute's value is the empty string, then set the returnValue attribute's value to the return value.

Otherwise

If the return value is a boolean with the value false, then the event must be canceled.


The Function interface represents a function in the scripting language being used. It is represented in IDL as follows:

[Callback=FunctionOnly, NoInterfaceObject]
interface Function {
  any call([Variadic] in any arguments);
};

The call(...) method is the object's callback.

In JavaScript, any Function object implements this interface.

5.5.6.2 Event handler attributes on elements, Document objects, and Window objects

The following are the event handler attributes (and their corresponding event handler event types) that must be supported by all HTML elements, as both content attributes and DOM attributes, and on Document and Window objects, as DOM attributes.

event handler attribute Event handler event type
onabort abort
oncanplay canplay
oncanplaythrough canplaythrough
onchange change
onclick click
oncontextmenu contextmenu
ondataunavailable dataunavailable
ondblclick dblclick
ondrag drag
ondragend dragend
ondragenter dragenter
ondragleave dragleave
ondragover dragover
ondragstart dragstart
ondrop drop
ondurationchange durationchange
onemptied emptied
onended ended
onformchange formchange
onforminput forminput
oninput input
oninvalid invalid
onkeydown keydown
onkeypress keypress
onkeyup keyup
onloadeddata loadeddata
onloadedmetadata loadedmetadata
onloadstart loadstart
onmousedown mousedown
onmousemove mousemove
onmouseout mouseout
onmouseover mouseover
onmouseup mouseup
onmousewheel mousewheel
onpause pause
onplay play
onplaying playing
onprogress progress
onratechange ratechange
onreadystatechange readystatechange
onscroll scroll
onseeked seeked
onseeking seeking
onselect select
onshow show
onstalled stalled
onsubmit submit
onsuspend suspend
ontimeupdate timeupdate
onvolumechange volumechange
onwaiting waiting

The following are the event handler attributes (and their corresponding event handler event types) that must be supported by all HTML elements other than body, as both content attributes and DOM attributes, and on Document objects, as DOM attributes:

event handler attribute Event handler event type
onblur blur
onerror error
onfocus focus
onload load

The following are the event handler attributes (and their corresponding event handler event types) that must be supported by Window objects, as DOM attributes on the Window object, and with corresponding content attributes and DOM attributes exposed on the body element:

event handler attribute Event handler event type
onafterprint afterprint
onbeforeprint beforeprint
onbeforeunload beforeunload
onblur blur
onerror error
onfocus focus
onhashchange hashchange
onload load
onmessage message
onoffline offline
ononline online
onpopstate popstate
onredo redo
onresize resize
onstorage storage
onundo undo
onunload unload

The onerror handler is also used for reporting script errors.

5.5.6.3 Event firing

maybe this should be moved higher up (terminology? conformance? DOM?) Also, the whole terminology thing should be changed so that we don't define any specific events here, we only define 'simple event', 'progress event', 'mouse event', 'key event', and the like, and have the actual dispatch use those generic terms when firing events.

Certain operations and methods are defined as firing events on elements. For example, the click() method on the HTMLElement interface is defined as firing a click event on the element. [DOM3EVENTS]

Firing a click event means that a click event with no namespace, which bubbles and is cancelable, and which uses the MouseEvent interface, must be dispatched at the given target. The event object must have its screenX, screenY, clientX, clientY, and button attributes set to 0, its ctrlKey, shiftKey, altKey, and metaKey attributes set according to the current state of the key input device, if any (false for any keys that are not available), its detail attribute set to 1, and its relatedTarget attribute set to null. The getModifierState() method on the object must return values appropriately describing the state of the key input device at the time the event is created.

Firing a simple event called e means that an event with the name e, with no namespace, which does not bubble (unless otherwise stated) and is not cancelable (unless otherwise stated), and which uses the Event interface, must be dispatched at the given target.

Firing a progress event called e means something that hasn't yet been defined, in the [PROGRESS] spec.

The default action of these event is to do nothing unless otherwise stated.

If you dispatch a custom "click" event at an element that would normally have default actions, should they get triggered? If so, we need to go through the entire spec and make sure that any default actions are defined in terms of any event of the right type on that element, not those that are dispatched in expected ways.

5.5.6.4 Events and the Window object

When an event is dispatched at a DOM node in a Document in a browsing context, if the event is not a load event, the user agent must also dispatch the event to the Window, as follows:

  1. In the capture phase, the event must be dispatched to the Window object before being dispatched to any of the nodes.
  2. In the bubble phase, the event must be dispatched to the Window object at the end of the phase, unless bubbling has been prevented.
5.5.6.5 Runtime script errors

This section only applies to user agents that support scripting in general and JavaScript in particular.

Whenever a runtime script error occurs in one of the scripts associated with a Document, the user agent must report the error using the onerror event handler attribute of the script's global object. If the error is still not handled after this, then the error should be reported to the user.


When the user agent is required to report an error error using the event handler attribute onerror, it must run these steps, after which the error is either handled or not handled:

If the value of onerror is a Function

The function must be invoked with three arguments. The three arguments passed to the function are all DOMStrings; the first must give the message that the UA is considering reporting, the second must give the absolute URL of the resource in which the error occurred, and the third must give the line number in that resource on which the error occurred.

If the function returns false, then the error is handled. Otherwise, the error is not handled.

Any exceptions thrown or errors caused by this function must be reported to the user immediately after the error that the function was called for, without using the report an error algorithm again.

Otherwise

The error is not handled.

5.6 User prompts

5.6.1 Simple dialogs

window . alert(message)

Displays a modal alert with the given message, and waits for the user to dismiss it.

A call to the navigator.getStorageUpdates() method is implied when this method is invoked.

result = window . confirm(message)

Displays a modal OK/Cancel prompt with the given message, waits for the user to dismiss it, and returns true if the user clicks OK and false if the user clicks Cancel.

A call to the navigator.getStorageUpdates() method is implied when this method is invoked.

result = window . prompt(message [, default] )

Displays a modal text field prompt with the given message, waits for the user to dismiss it, and returns the value that the user entered. If the user cancels the prompt, then returns null instead. If the second argument is present, then the given value is used as a default.

A call to the navigator.getStorageUpdates() method is implied when this method is invoked.

The alert(message) method, when invoked, must release the storage mutex and show the given message to the user. The user agent may make the method wait for the user to acknowledge the message before returning; if so, the user agent must pause while the method is waiting.

The confirm(message) method, when invoked, must release the storage mutex and show the given message to the user, and ask the user to respond with a positive or negative response. The user agent must then pause as the method waits for the user's response. If the user responds positively, the method must return true, and if the user responds negatively, the method must return false.

The prompt(message, default) method, when invoked, must release the storage mutex, show the given message to the user, and ask the user to either respond with a string value or abort. The user agent must then pause as the method waits for the user's response. The second argument is optional. If the second argument (default) is present, then the response must be defaulted to the value given by default. If the user aborts, then the method must return null; otherwise, the method must return the string that the user responded with.

5.6.2 Printing

window . print()

Prompts the user to print the page.

A call to the navigator.getStorageUpdates() method is implied when this method is invoked.

The print() method, when invoked, must run the printing steps.

User agents should also run the printing steps whenever the user asks for the opportunity to obtain a physical form (e.g. printed copy), or the representation of a physical form (e.g. PDF copy), of a document.

The printing steps are as follows:

  1. The user agent may display a message to the user and/or may abort these steps.

    For instance, a kiosk browser could silently ignore any invocations of the print() method.

    For instance, a browser on a mobile device could detect that there are no printers in the vicinity and display a message saying so before continuing to offer a "save to PDF" option.

  2. The user agent must fire a simple event called beforeprint at the Window object of the Document that is being printed, as well as any nested browsing contexts in it.

    The beforeprint event can be used to annotate the printed copy, for instance adding the time at which the document was printed.

  3. The user agent must release the storage mutex.

  4. The user agent should offer the user the opportunity to obtain a physical form (or the representation of a physical form) of the document. The user agent may wait for the user to either accept or decline before returning; if so, the user agent must pause while the method is waiting. Even if the user agent doesn't wait at this point, the user agent must use the state of the relevant documents as they are at this point in the algorithm if and when it eventually creates the alternate form.

  5. The user agent must fire a simple event called afterprint at the Window object of the Document that is being printed, as well as any nested browsing contexts in it.

    The afterprint event can be used to revert annotations added in the earlier event, as well as showing post-printing UI. For instance, if a page is walking the user through the steps of applying for a home loan, the script could automatically advance to the next step after having printed a form or other.

5.6.3 Dialogs implemented using separate documents

result = window . showModalDialog(url [, argument] )

Prompts the user with the given page, waits for that page to close, and returns the return value.

A call to the navigator.getStorageUpdates() method is implied when this method is invoked.

The showModalDialog(url, argument) method, when invoked, must cause the user agent to run the following steps:

  1. Resolve url relative to the first script's base URL.

    If this fails, then throw a SYNTAX_ERR exception and abort these steps.

  2. Release the storage mutex.

  3. If the user agent is configured such that this invocation of showModalDialog() is somehow disabled, then the method returns the empty string; abort these steps.

    User agents are expected to disable this method in certain cases to avoid user annoyance (e.g. as part of their popup blocker feature). For instance, a user agent could require that a site be white-listed before enabling this method, or the user agent could be configured to only allow one modal dialog at a time.

  4. Let the list of background browsing contexts be a list of all the browsing contexts that:

    ...as well as any browsing contexts that are nested inside any of the browsing contexts matching those conditions.

  5. Disable the user interface for all the browsing contexts in the list of background browsing contexts. This should prevent the user from navigating those browsing contexts, causing events to be sent to those browsing context, or editing any content in those browsing contexts. However, it does not prevent those browsing contexts from receiving events from sources other than the user, from running scripts, from running animations, and so forth.

  6. Create a new auxiliary browsing context, with the opener browsing context being the browsing context of the Window object on which the showModalDialog() method was called. The new auxiliary browsing context has no name.

    This browsing context's Documents' Window objects all implement the WindowModal interface.

  7. Let the dialog arguments of the new browsing context be set to the value of argument, or the 'undefined' value if the argument was omitted.

  8. Let the dialog arguments' origin be the origin of the script that called the showModalDialog() method.

  9. Navigate the new browsing context to the absolute URL that resulted from resolving url earlier, with replacement enabled, and with the browsing context of the script that invoked the method as the source browsing context.

  10. Wait for the browsing context to be closed. (The user agent must allow the user to indicate that the browsing context is to be closed.)

  11. Reenable the user interface for all the browsing contexts in the list of background browsing contexts.

  12. Return the auxiliary browsing context's return value.

The Window objects of Documents hosted by browsing contexts created by the above algorithm must all implement the WindowModal interface:

Really I want the Window object to just gain these attributes, as if they were on the Window prototype. That's the XXX below.

[NoInterfaceObject, ImplementedOn=Window, XXX] interface WindowModal {
  readonly attribute any dialogArguments;
           attribute DOMString returnValue;
};
window . dialogArguments

Returns the argument argument that was passed to the showModalDialog() method.

window . returnValue [ = value ]

Returns the current return value for the window.

Can be set, to change the value that will be returned by the showModalDialog() method.

Such browsing contexts have associated dialog arguments, which are stored along with the dialog arguments' origin. These values are set by the showModalDialog() method in the algorithm above, when the browsing context is created, based on the arguments provided to the method.

The dialogArguments DOM attribute, on getting, must check whether its browsing context's active document's origin is the same as the dialog arguments' origin. If it is, then the browsing context's dialog arguments must be returned unchanged. Otherwise, if the dialog arguments are an object, then the empty string must be returned, and if the dialog arguments are not an object, then the stringification of the dialog arguments must be returned.

These browsing contexts also have an associated return value. The return value of a browsing context must be initialized to the empty string when the browsing context is created.

The returnValue DOM attribute, on getting, must return the return value of its browsing context, and on setting, must set the return value to the given new value.

The window.close() method can be used to close the browsing context.

5.7 System state and capabilities

The navigator attribute of the Window interface must return an instance of the Navigator interface, which represents the identity and state of the user agent (the client), and allows Web pages to register themselves as potential protocol and content handlers:

interface Navigator {
  // objects implementing this interface also implement the interfaces given below
};

[NoInterfaceObject, ImplementedOn=Navigator] interface NavigatorID {
  readonly attribute DOMString appName;
  readonly attribute DOMString appVersion;
  readonly attribute DOMString platform;
  readonly attribute DOMString userAgent;
};

[NoInterfaceObject, ImplementedOn=Navigator] interface NavigatorOnLine {
  readonly attribute boolean onLine;
};

[NoInterfaceObject, ImplementedOn=Navigator] interface NavigatorAbilities {
  // content handler registration
  void registerProtocolHandler(in DOMString protocol, in DOMString url, in DOMString title);
  void registerContentHandler(in DOMString mimeType, in DOMString url, in DOMString title);
  void getStorageUpdates();
};

Objects implementing the Navigator interface must also implement the NavigatorID, NavigatorOnLine, and NavigatorAbilities interfaces. (These interfaces are defined separately so that other specifications can re-use parts of the Navigator interface.)

5.7.1 Client identification

In certain cases, despite the best efforts of the entire industry, Web browsers have bugs and limitations that Web authors are forced to work around.

This section defines a collection of attributes that can be used to determine, from script, the kind of user agent in use, in order to work around these issues.

Client detection should always be limited to detecting known current versions; future versions and unknown versions should always be assumed to be fully compliant.

window . navigator . appName

Returns the name of the browser.

window . navigator . appVersion

Returns the version of the browser.

window . navigator . platform

Returns the name of the platform.

window . navigator . userAgent

Returns the complete User-Agent header.

appName

Must return either the string "Netscape" or the full name of the browser, e.g. "Mellblom Browsernator".

appVersion

Must return either the string "4.0" or a string representing the version of the browser in detail, e.g. "1.0 (VMS; en-US) Mellblomenator/9000".

platform

Must return either the empty string or a string representing the platform on which the browser is executing, e.g. "MacIntel", "Win32", "FreeBSD i386", "WebTV OS".

userAgent

Must return the string used for the value of the "User-Agent" header in HTTP requests, or the empty string if no such header is ever sent.

5.7.2 Custom protocol and content handlers

The registerProtocolHandler() method allows Web sites to register themselves as possible handlers for particular protocols. For example, an online fax service could register itself as a handler of the fax: protocol ([RFC2806]), so that if the user clicks on such a link, he is given the opportunity to use that Web site. Analogously, the registerContentHandler() method allows Web sites to register themselves as possible handlers for content in a particular MIME type. For example, the same online fax service could register itself as a handler for image/g3fax files ([RFC1494]), so that if the user has no native application capable of handling G3 Facsimile byte streams, his Web browser can instead suggest he use that site to view the image.

window . navigator . registerProtocolHandler(protocol, url, title)
window . navigator . registerContentHandler(mimeType, url, title)

Registers a handler for the given protocol or content type, at the given URL, with the given title.

The string "%s" in the URL is used as a placeholder for where to put the URL of the content to be handled.

Throws a SECURITY_ERR exception if the user agent blocks the registration (this might happen if trying to register as a handler for "http", for instance).

Throws a SYNTAX_ERR if the "%s" string is missing in the URL.

User agents may, within the constraints described in this section, do whatever they like when the methods are called. A UA could, for instance, prompt the user and offer the user the opportunity to add the site to a shortlist of handlers, or make the handlers his default, or cancel the request. UAs could provide such a UI through modal UI or through a non-modal transient notification interface. UAs could also simply silently collect the information, providing it only when relevant to the user.

There is an example of how these methods could be presented to the user below.

The arguments to the methods have the following meanings and corresponding implementation requirements:

protocol (registerProtocolHandler() only)

A scheme, such as ftp or fax. The scheme must be compared in an ASCII case-insensitive manner by user agents for the purposes of comparing with the scheme part of URLs that they consider against the list of registered handlers.

The protocol value, if it contains a colon (as in "ftp:"), will never match anything, since schemes don't contain colons.

mimeType (registerContentHandler() only)

A MIME type, such as model/vrml or text/richtext. The MIME type must be compared in an ASCII case-insensitive manner by user agents for the purposes of comparing with MIME types of documents that they consider against the list of registered handlers.

User agents must compare the given values only to the MIME type/subtype parts of content types, not to the complete type including parameters. Thus, if mimeType values passed to this method include characters such as commas or whitespace, or include MIME parameters, then the handler being registered will never be used.

url

The URL of the page that will handle the requests.

When the user agent uses this URL, it must replace the first occurrence of the exact literal string "%s" with an escaped version of the absolute URL of the content in question (as defined below), then resolve the resulting URL, relative to the base URL of the first script at the time the registerContentHandler() or registerProtocolHandler() methods were invoked, and then fetch the resulting URL using the GET method (or equivalent for non-HTTP URLs).

To get the escaped version of the absolute URL of the content in question, the user agent must replace every character in that absolute URL that doesn't match the <query> production defined in RFC 3986 by the percent-encoded form of that character. [RFC3986]

If the user had visited a site at http://example.com/ that made the following call:

navigator.registerContentHandler('application/x-soup', 'soup?url=%s', 'SoupWeb™')

...and then, much later, while visiting http://www.example.net/, clicked on a link such as:

<a href="chickenkïwi.soup">Download our Chicken Kïwi soup!</a>

...then, assuming this chickenkïwi.soup file was served with the MIME type application/x-soup, the UA might navigate to the following URL:

http://example.com/soup?url=http://www.example.net/chickenk%C3%AFwi.soup

This site could then fetch the chickenkïwi.soup file and do whatever it is that it does with soup (synthesize it and ship it to the user, or whatever).

title

A descriptive title of the handler, which the UA might use to remind the user what the site in question is.

User agents should raise SECURITY_ERR exceptions if the methods are called with protocol or mimeType values that the UA deems to be "privileged". For example, a site attempting to register a handler for http URLs or text/html content in a Web browser would likely cause an exception to be raised.

User agents must raise a SYNTAX_ERR exception if the url argument passed to one of these methods does not contain the exact literal string "%s", or if resolving the url argument with the first occurrence of the string "%s" removed, relative to the first script's base URL, is not successful.

User agents must not raise any other exceptions (other than binding-specific exceptions, such as for an incorrect number of arguments in an JavaScript implementation).

This section does not define how the pages registered by these methods are used, beyond the requirements on how to process the url value (see above). To some extent, the processing model for navigating across documents defines some cases where these methods are relevant, but in general UAs may use this information wherever they would otherwise consider handing content to native plugins or helper applications.

UAs must not use registered content handlers to handle content that was returned as part of a non-GET transaction (or rather, as part of any non-idempotent transaction), as the remote site would not be able to fetch the same data.

5.7.2.1 Security and privacy

These mechanisms can introduce a number of concerns, in particular privacy concerns.

Hijacking all Web usage. User agents should not allow protocols that are key to its normal operation, such as http or https, to be rerouted through third-party sites. This would allow a user's activities to be trivially tracked, and would allow user information, even in secure connections, to be collected.

Hijacking defaults. It is strongly recommended that user agents do not automatically change any defaults, as this could lead the user to send data to remote hosts that the user is not expecting. New handlers registering themselves should never automatically cause those sites to be used.

Registration spamming. User agents should consider the possibility that a site will attempt to register a large number of handlers, possibly from multiple domains (e.g. by redirecting through a series of pages each on a different domain, and each registering a handler for video/mpeg — analogous practices abusing other Web browser features have been used by pornography Web sites for many years). User agents should gracefully handle such hostile attempts, protecting the user.

Misleading titles. User agents should not rely wholly on the title argument to the methods when presenting the registered handlers to the user, since sites could easily lie. For example, a site hostile.example.net could claim that it was registering the "Cuddly Bear Happy Content Handler". User agents should therefore use the handler's domain in any UI along with any title.

Hostile handler metadata. User agents should protect against typical attacks against strings embedded in their interface, for example ensuring that markup or escape characters in such strings are not executed, that null bytes are properly handled, that over-long strings do not cause crashes or buffer overruns, and so forth.

Leaking Intranet URLs. The mechanism described in this section can result in secret Intranet URLs being leaked, in the following manner:

  1. The user registers a third-party content handler as the default handler for a content type.
  2. The user then browses his corporate Intranet site and accesses a document that uses that content type.
  3. The user agent contacts the third party and hands the third party the URL to the Intranet content.

No actual confidential file data is leaked in this manner, but the URLs themselves could contain confidential information. For example, the URL could be http://www.corp.example.com/upcoming-aquisitions/the-sample-company.egf, which might tell the third party that Example Corporation is intending to merge with The Sample Company. Implementors might wish to consider allowing administrators to disable this feature for certain subdomains, content types, or protocols.

Leaking secure URLs. User agents should not send HTTPS URLs to third-party sites registered as content handlers, in the same way that user agents do not send Referer (sic) HTTP headers from secure sites to third-party sites.

Leaking credentials. User agents must never send username or password information in the URLs that are escaped and included sent to the handler sites. User agents may even avoid attempting to pass to Web-based handlers the URLs of resources that are known to require authentication to access, as such sites would be unable to access the resources in question without prompting the user for credentials themselves (a practice that would require the user to know whether to trust the third-party handler, a decision many users are unable to make or even understand).

5.7.2.2 Sample user interface

This section is non-normative.

A simple implementation of this feature for a desktop Web browser might work as follows.

The registerProtocolHandler() method could display a modal dialog box:

||[ Protocol Handler Registration ]|||||||||||||||||||||||||||
|                                                            |
| This Web page:                                             |
|                                                            |
|    Kittens at work                                         |
|    http://kittens.example.org/                             |
|                                                            |
| ...would like permission to handle the protocol "x-meow:"  |
| using the following Web-based application:                 |
|                                                            |
|    Kittens-at-work displayer                               |
|    http://kittens.example.org/?show=%s                     |
|                                                            |
| Do you trust the administrators of the "kittens.example.   |
| org" domain?                                               |
|                                                            |
|              ( Trust kittens.example.org )  (( Cancel ))   |
|____________________________________________________________|

...where "Kittens at work" is the title of the page that invoked the method, "http://kittens.example.org/" is the URL of that page, "x-meow" is the string that was passed to the registerProtocolHandler() method as its first argument (protocol), "http://kittens.example.org/?show=%s" was the second argument (url), and "Kittens-at-work displayer" was the third argument (title).

If the user clicks the Cancel button, then nothing further happens. If the user clicks the "Trust" button, then the handler is remembered.

When the user then attempts to fetch a URL that uses the "x-meow:" scheme, then it might display a dialog as follows:

||[ Unknown Protocol ]||||||||||||||||||||||||||||||||||||||||
|                                                            |
| You have attempted to access:                              |
|                                                            |
|    x-meow:S2l0dGVucyBhcmUgdGhlIGN1dGVzdCE%3D               |
|                                                            |
| How would you like FerretBrowser to handle this resource?  |
|                                                            |
|  (o) Contact the FerretBrowser plugin registry to see if   |
|      there is an official way to handle this resource.     |
|                                                            |
|  ( ) Pass this URL to a local application:                 |
|      [ /no application selected/             ] ( Choose )  |
|                                                            |
|  ( ) Pass this URL to the "Kittens-at-work displayer"      |
|      application at "kittens.example.org".                 |
|                                                            |
|  [ ] Always do this for resources using the "x-meow"       |
|      protocol in future.                                   |
|                                                            |
|                                     ( Ok )  (( Cancel ))   |
|____________________________________________________________|

...where the third option is the one that was primed by the site registering itself earlier.

If the user does select that option, then the browser, in accordance with the requirements described in the previous two sections, will redirect the user to "http://kittens.example.org/?show=x-meow%3AS2l0dGVucyBhcmUgdGhlIGN1dGVzdCE%253D".

The registerContentHandler() method would work equivalently, but for unknown MIME types instead of unknown protocols.

5.7.3 Manually releasing the storage mutex

window . navigator . getStorageUpdates()

If a script uses the document.cookie API, or the localStorage API, the browser will block other scripts from accessing cookies or storage until the first script finishes.

Calling the navigator.getStorageUpdates() method tells the user agent to unblock any other scripts that may be blocked, even though the script hasn't returned.

Values of cookies and items in the Storage objects of localStorage attributes can change after calling this method, whence its name.

The getStorageUpdates() method, when invoked, must, if the storage mutex is owned by the event loop of the task that resulted in the method being called, release the storage mutex so that it is once again free. Otherwise, it must do nothing.

5.8 Offline Web applications

5.8.1 Introduction

This section is non-normative.

...

5.8.2 Application caches

An application cache is a set of cached resources consisting of:

Each application cache has a completeness flag, which is either complete or incomplete.


An application cache group is a group of application caches, identified by the absolute URL of a resource manifest which is used to populate the caches in the group.

An application cache is newer than another if it was created after the other (in other words, application caches in an application cache group have a chronological order).

Only the newest application cache in an application cache group can have its completeness flag set to incomplete, the others are always all complete.

Each application cache group has an update status, which is one of the following: idle, checking, downloading.

A relevant application cache is an application cache that is the newest in its group to be complete.

Each application cache group has a list of pending master entries. Each entry in this list consists of a resource and a corresponding Document object. It is used during the update process to ensure that new master entries are cached.

An application cache group can be marked as obsolete, meaning that it must be ignored when looking at what application cache groups exist.


A cache host is a Document or a SharedWorkerGlobalScope object. A cache host can be associated with an application cache.

A Document initially is not associated with an application cache, but can become associated with one early during the page load process, when steps in the parser and in the navigation sections cause cache selection to occur.

A SharedWorkerGlobalScope can be associated with an application cache when it is created.

Each cache host has an associated ApplicationCache object.


Multiple application caches in different application cache groups can contain the same resource, e.g. if the manifests all reference that resource. If the user agent is to select an application cache from a list of relevant application caches that contain a resource, that the user agent must use the application cache that the user most likely wants to see the resource from, taking into account the following:

5.8.3 The cache manifest syntax

5.8.3.1 A sample manifest

This section is non-normative.

This example manifest requires two images and a style sheet to be cached and whitelists a CGI script.

CACHE MANIFEST
# the above line is required

# this is a comment
# there can be as many of these anywhere in the file
# they are all ignored
  # comments can have spaces before them
  # but must be alone on the line

# blank lines are ignored too

# these are files that need to be cached they can either be listed
# first, or a "CACHE:" header could be put before them, as is done
# lower down.
images/sound-icon.png
images/background.png
# note that each file has to be put on its own line

# here is a file for the online whitelist -- it isn't cached, and 
# references to this file will bypass the cache, always hitting the
# network (or trying to, if the user is offline).
NETWORK:
comm.cgi

# here is another set of files to cache, this time just the CSS file.
CACHE:
style/default.css
5.8.3.2 Writing cache manifests

Manifests must be served using the text/cache-manifest MIME type. All resources served using the text/cache-manifest MIME type must follow the syntax of application cache manifests, as described in this section.

An application cache manifest is a text file, whose text is encoded using UTF-8. Data in application cache manifests is line-based. Newlines must be represented by U+000A LINE FEED (LF) characters, U+000D CARRIAGE RETURN (CR) characters, or U+000D CARRIAGE RETURN (CR) U+000A LINE FEED (LF) pairs.

This is a willful double violation of RFC2046. [RFC2046]

The first line of an application cache manifest must consist of the string "CACHE", a single U+0020 SPACE character, the string "MANIFEST", and either a U+0020 SPACE character, a U+0009 CHARACTER TABULATION (tab) character, a U+000A LINE FEED (LF) character, or a U+000D CARRIAGE RETURN (CR) character. The first line may optionally be preceded by a U+FEFF BYTE ORDER MARK (BOM) character. If any other text is found on the first line, it is ignored.

Subsequent lines, if any, must all be one of the following:

A blank line

Blank lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters only.

A comment

Comment lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, followed by a single U+0023 NUMBER SIGN (#) character, followed by zero or more characters other than U+000A LINE FEED (LF) and U+000D CARRIAGE RETURN (CR) characters.

Comments must be on a line on their own. If they were to be included on a line with a URL, the "#" would be mistaken for part of a fragment identifier.

A section header

Section headers change the current section. There are three possible section headers:

CACHE:
Switches to the explicit section.
FALLBACK:
Switches to the fallback section.
NETWORK:
Switches to the online whitelist section.

Section header lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, followed by one of the names above (including the U+003A COLON (:) character) followed by zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters.

Ironically, by default, the current section is the explicit section.

Data for the current section

The format that data lines must take depends on the current section.

When the current section is the explicit section or the online whitelist section, data lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, a valid URL identifying a resource other than the manifest itself, and then zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters.

When the current section is the fallback section, data lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, a valid URL identifying a resource other than the manifest itself, one or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, another valid URL identifying a resource other than the manifest itself, and then zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters.

The URLs in data lines can't be empty strings, since those would be relative URLs to the manifest itself. Such lines would be confused with blank or invalid lines, anyway.

Manifests may contain sections more than once. Sections may be empty.

URLs that are to be fallback pages associated with fallback namespaces, and those namespaces themselves, must be given in fallback sections, with the namespace being the first URL of the data line, and the corresponding fallback page being the second URL. All the other pages to be cached must be listed in explicit sections.

Fallback namespaces and fallback entries must have the same origin as the manifest itself.

A fallback namespace must not be listed more than once.

URLs that the user agent is to put into the online whitelist must all be specified in online whitelist sections. (This is needed for any URL that the page is intending to use to communicate back to the server.)

Relative URLs must be given relative to the manifest's own URL.

URLs in manifests must not have fragment identifiers (i.e. the U+0023 NUMBER SIGN character isn't allowed in URLs in manifests).

5.8.3.3 Parsing cache manifests

When a user agent is to parse a manifest, it means that the user agent must run the following steps:

  1. The user agent must decode the byte stream corresponding with the manifest to be parsed, treating it as UTF-8. Bytes or sequences of bytes that are not valid UTF-8 sequences must be interpreted as a U+FFFD REPLACEMENT CHARACTER.

  2. Let base URL be the absolute URL representing the manifest.

  3. Let explicit URLs be an initially empty list of explicit entries.

  4. Let fallback URLs be an initially empty mapping of fallback namespaces to fallback entries.

  5. Let online whitelist URLs be an initially empty list of URLs for a online whitelist.

  6. Let input be the decoded text of the manifest's byte stream.

  7. Let position be a pointer into input, initially pointing at the first character.

  8. If position is pointing at a U+FEFF BYTE ORDER MARK (BOM) character, then advance position to the next character.

  9. If the characters starting from position are "CACHE", followed by a U+0020 SPACE character, followed by "MANIFEST", then advance position to the next character after those. Otherwise, this isn't a cache manifest; abort this algorithm with a failure while checking for the magic signature.

  10. If the character at position is neither a U+0020 SPACE character, a U+0009 CHARACTER TABULATION (tab) character, U+000A LINE FEED (LF) character, nor a U+000D CARRIAGE RETURN (CR) character, then this isn't a cache manifest; abort this algorithm with a failure while checking for the magic signature.

  11. This is a cache manifest. The algorithm cannot fail beyond this point (though bogus lines can get ignored).

  12. Collect a sequence of characters that are not U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters, and ignore those characters. (Extra text on the first line, after the signature, is ignored.)

  13. Let mode be "explicit".

  14. Start of line: If position is past the end of input, then jump to the last step. Otherwise, collect a sequence of characters that are U+000A LINE FEED (LF), U+000D CARRIAGE RETURN (CR), U+0020 SPACE, or U+0009 CHARACTER TABULATION (tab) characters.

  15. Now, collect a sequence of characters that are not U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters, and let the result be line.

  16. Drop any trailing U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters at the end of line.

  17. If line is the empty string, then jump back to the step labeled "start of line".

  18. If the first character in line is a U+0023 NUMBER SIGN (#) character, then jump back to the step labeled "start of line".

  19. If line equals "CACHE:" (the word "CACHE" followed by a U+003A COLON (:) character), then set mode to "explicit" and jump back to the step labeled "start of line".

  20. If line equals "FALLBACK:" (the word "FALLBACK" followed by a U+003A COLON (:) character), then set mode to "fallback" and jump back to the step labeled "start of line".

  21. If line equals "NETWORK:" (the word "NETWORK" followed by a U+003A COLON (:) character), then set mode to "online whitelist" and jump back to the step labeled "start of line".

  22. If line ends with a U+003A COLON (:) character, then set mode to "unknown" and jump back to the step labeled "start of line".

  23. This is either a data line or it is syntactically incorrect.

  24. Let position be a pointer into line, initially pointing at the start of the string.

  25. Let tokens be a list of strings, initially empty.

  26. While position doesn't point past the end of line:

    1. Let current token be an empty string.

    2. While position doesn't point past the end of line and the character at position is neither a U+0020 SPACE nor a U+0009 CHARACTER TABULATION (tab) character, add the character at position to current token and advance position to the next character in input.

    3. Add current token to the tokens list.

    4. While position doesn't point past the end of line and the character at position is either a U+0020 SPACE or a U+0009 CHARACTER TABULATION (tab) character, advance position to the next character in input.

  27. Process tokens as follows:

    If mode is "explicit"

    Resolve the first item in tokens, relative to base URL; ignore the rest.

    If this fails, then jump back to the step labeled "start of line".

    If the resulting absolute URL has a different <scheme> component than the manifest's URL (compared in an ASCII case-insensitive manner), then jump back to the step labeled "start of line".

    Drop the <fragment> component of the resulting absolute URL, if it has one.

    Add the resulting absolute URL to the explicit URLs.

    If mode is "fallback"

    Let part one be the first token in tokens, and let part two be the second token in tokens.

    Resolve part one and part two, relative to base URL.

    If either fails, then jump back to the step labeled "start of line".

    If the absolute URL corresponding to either part one or part two does not have the same origin as the manifest's URL, then jump back to the step labeled "start of line".

    Drop any the <fragment> components of the resulting absolute URLs.

    If the absolute URL corresponding to part one is already in the fallback URLs mapping as a fallback namespace, then jump back to the step labeled "start of line".

    Otherwise, add the absolute URL corresponding to part one to the fallback URLs mapping as a fallback namespace, mapped to the absolute URL corresponding to part two as the fallback entry.

    If mode is "online whitelist"

    Resolve the first item in tokens, relative to base URL; ignore the rest.

    If this fails, then jump back to the step labeled "start of line".

    If the resulting absolute URL has a different <scheme> component than the manifest's URL (compared in an ASCII case-insensitive manner), then jump back to the step labeled "start of line".

    Drop the <fragment> component of the resulting absolute URL, if it has one.

    Add the resulting absolute URL to the online whitelist URLs.

    If mode is "unknown"

    Do nothing. The line is ignored.

  28. Jump back to the step labeled "start of line". (That step jumps to the next, and last, step when the end of the file is reached.)

  29. Return the explicit URLs list, the fallback URLs mapping, and the online whitelist URLs.

If a resource is listed in the explicit section and matches an entry in the online whitelist, or if a resource matches both an entry in the fallback section and the online whitelist, the resource will taken from the cache, and the online whitelist entry will be ignored.

5.8.4 Updating an application cache

When the user agent is required (by other parts of this specification) to start the application cache update process for an absolute URL purported to identify a manifest, or for an application cache group, potentially given a particular cache host, and potentially given a new master resource, the user agent must run the following steps:

  1. Atomically, so as to avoid race conditions, perform the following substeps:

    1. Pick the appropriate substeps:

      If these steps were invoked with an absolute URL purported to identify a manifest

      Let manifest URL be that absolute URL.

      If there is no application cache group identified by manifest URL, then create a new application cache group identified by manifest URL. Initially, it has no application caches. One will be created later in this algorithm.

      If these steps were invoked with an application cache group

      Let manifest URL be the absolute URL of the manifest used to identify the application cache group to be updated.

    2. Let cache group be the application cache group identified by manifest URL.

    3. If these steps were invoked with a new master resource, then add the resource, along with the resource's Document, to cache group's list of pending master entries.

    4. If these steps were invoked with a cache host, and the status of cache group is checking or downloading, then queue a task to fire a simple event called checking at the ApplicationCache singleton of that cache host. The default action of this event should be the display of some sort of user interface indicating to the user that the user agent is checking to see if it can download the application.

    5. If these steps were invoked with a cache host, and the status of cache group is downloading, then also queue a task to fire a simple event called downloading that is cancelable at the ApplicationCache singleton of that cache host. The default action of this event should be the display of some sort of user interface indicating to the user the application is being downloaded.

    6. If the status of the cache group is either checking or downloading, then abort this instance of the update process, as an update is already in progress for them.

    7. Set the status of cache group to checking.

    8. For each cache host associated with an application cache in cache group, queue a task to fire a simple event that is cancelable called checking at the ApplicationCache singleton of the cache host. The default action of these events should be the display of some sort of user interface indicating to the user that the user agent is checking for the availability of updates.

    The remainder of the steps run asynchronously.

    If cache group already has an application cache in it, then this is an upgrade attempt. Otherwise, this is a cache attempt.

  2. If this is a cache attempt, then this algorithm was invoked with a cache host; queue a task to fire a simple event called checking that is cancelable at the ApplicationCache singleton of that cache host. The default action of this event should be the display of some sort of user interface indicating to the user that the user agent is checking for the availability of updates.

  3. Fetching the manifest: Fetch the resource from manifest URL, and let manifest be that resource.

    If the resource is labeled with the MIME type text/cache-manifest, parse manifest according to the rules for parsing manifests, obtaining a list of explicit entries, fallback entries and the fallback namespaces that map to them, and entries for the online whitelist.

  4. If fetching the manifest fails due to a 404 or 410 response or equivalent, then run these substeps:

    1. Mark cache group as obsolete. This cache group no longer exists for any purpose other than the processing of Document objects already associated with an application cache in the cache group.

    2. For each cache host associated with an application cache in cache group, queue a task to fire a simple event called obsolete that is cancelable at the ApplicationCache singleton of the cache host. The default action of these events should be the display of some sort of user interface indicating to the user that the application is no longer available for offline use.

    3. For each entry in cache group's list of pending master entries, queue a task to fire a simple event that is cancelable called error (not obsolete!) at the ApplicationCache singleton of the cache host the Document for this entry, if there still is one. The default action of this event should be the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

    4. If cache group has an application cache whose completeness flag is incomplete, then discard that application cache.

    5. If appropriate, remove any user interface indicating that an update for this cache is in progress.

    6. Let the status of cache group be idle.

    7. Abort the update process.

  5. Otherwise, if fetching the manifest fails in some other way (e.g. the server returns another 4xx or 5xx response or equivalent, or there is a DNS error, or the connection times out, or the user cancels the download, or the parser for manifests fails when checking the magic signature), or if the server returned a redirect, or if the resource is labeled with a MIME type other than text/cache-manifest, then run the cache failure steps.

  6. If this is an upgrade attempt and the newly downloaded manifest is byte-for-byte identical to the manifest found in the newest application cache in cache group, or the server reported it as "304 Not Modified" or equivalent, then run these substeps:

    1. Let cache be the newest application cache in cache group.

    2. For each entry in cache group's list of pending master entries, wait for the resource for this entry to have either completely downloaded or failed.

      If the download failed (e.g. the connection times out, or the user cancels the download), then queue a task to fire a simple event that is cancelable called error at the ApplicationCache singleton of the cache host the Document for this entry, if there still is one. The default action of this event should be the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

      Otherwise, associate the Document for this entry with cache; store the resource for this entry in cache, if it isn't already there, and categorize its entry as a master entry.

      HTTP caching rules, such as Cache-Control: no-store, are ignored for the purposes of the application cache update process.

    3. For each cache host associated with an application cache in cache group, queue a task to fire a simple event that is cancelable called noupdate at the ApplicationCache singleton of the cache host. The default action of these events should be the display of some sort of user interface indicating to the user that the application is up to date.

    4. Empty cache group's list of pending master entries.

    5. If appropriate, remove any user interface indicating that an update for this cache is in progress.

    6. Let the status of cache group be idle.

    7. Abort the update process.

  7. Let new cache be a newly created application cache in cache group. Set its completeness flag to incomplete.

  8. For each entry in cache group's list of pending master entries, associate the Document for this entry with new cache.

  9. Set the status of cache group to downloading.

  10. For each cache host associated with an application cache in cache group, queue a task to fire a simple event that is cancelable called downloading at the ApplicationCache singleton of the cache host. The default action of these events should be the display of some sort of user interface indicating to the user that a new version is being downloaded.

  11. Let file list be an empty list of URLs with flags.

  12. Add all the URLs in the list of explicit entries obtained by parsing manifest to file list, each flagged with "explicit entry".

  13. Add all the URLs in the list of fallback entries obtained by parsing manifest to file list, each flagged with "fallback entry".

  14. If this is an upgrade attempt, then add all the URLs of master entries in the newest application cache in cache group whose completeness flag is complete to file list, each flagged with "master entry".

  15. If any URL is in file list more than once, then merge the entries into one entry for that URL, that entry having all the flags that the original entries had.

  16. For each URL in file list, run the following steps. These steps may be run in parallel for two or more of the URLs at a time.

    1. If the resource URL being processed was flagged as neither an "explicit entry" nor or a "fallback entry", then the user agent may skip this URL.

      This is intended to allow user agents to expire resources not listed in the manifest (other than those in the manifest itself) from the cache. Generally, implementors are urged to use an approach that expires lesser-used resources first.

    2. For each cache host associated with an application cache in cache group, queue a task to fire a simple event that is cancelable called progress at the ApplicationCache singleton of the cache host. The default action of these events should be the display of some sort of user interface indicating to the user that a file is being downloaded in preparation for updating the application.

    3. Fetch the resource. If this is an upgrade attempt, then use the newest application cache in cache group as an HTTP cache, and honor HTTP caching semantics (such as expiration, ETags, and so forth) with respect to that cache. User agents may also have other caches in place that are also honored.

      If the resource in question is already being downloaded for other reasons then the existing download process can be used for the purposes of this step, as defined by the fetching algorithm.

      An example of a resource that might already be being downloaded is a large image on a Web page that is being seen for the first time. The image would get downloaded to satisfy the img element on the page, as well as being listed in the cache manifest. According to the rules for fetching that image only need be downloaded once, and it can be used both for the cache and for the rendered Web page.

    4. If the previous step fails (e.g. the server returns a 4xx or 5xx response or equivalent, or there is a DNS error, or the connection times out, or the user cancels the download), or if the server returned a redirect, then run the first appropriate step from the following list:

      If the URL being processed was flagged as an "explicit entry" or a "fallback entry"

      Run the cache failure steps.

      Redirects are fatal because they are either indicative of a network problem (e.g. a captive portal); or would allow resources to be added to the cache under URLs that differ from any URL that the networking model will allow access to, leaving orphan entries; or would allow resources to be stored under URLs different than their true URLs. All of these situations are bad.

      If the error was a 404 or 410 HTTP response or equivalent

      Skip this resource. It is dropped from the cache.

      Otherwise

      Copy the resource and its metadata from the newest application cache in cache group whose completeness flag is complete, and act as if that was the fetched resource, ignoring the resource obtained from the network.

      User agents may warn the user of these errors as an aid to development.

      These rules make errors for resources listed in the manifest fatal, while making it possible for other resources to be removed from caches when they are removed from the server, without errors, and making non-manifest resources survive server-side errors.

    5. Otherwise, the fetching succeeded. Store the resource in the new cache.

    6. If the URL being processed was flagged as an "explicit entry" in file list, then categorize the entry as an explicit entry.

    7. If the URL being processed was flagged as a "fallback entry" in file list, then categorize the entry as a fallback entry.

    8. If the URL being processed was flagged as an "master entry" in file list, then categorize the entry as a master entry.

    9. As an optimization, if the resource is an HTML or XML file whose root element is an html element with a manifest attribute whose value doesn't match the manifest URL of the application cache being processed, then the user agent should mark the entry as being foreign.

  17. Store the list of fallback namespaces, and the URLs of the fallback entries that they map to, in new cache.

  18. Store the URLs that form the new online whitelist in new cache.

  19. For each entry in cache group's list of pending master entries, wait for the resource for this entry to have either completely downloaded or failed.

    If the download failed (e.g. the connection times out, or the user cancels the download), then run these substeps:

    1. Unassociate the Document for this entry from new cache.

    2. Queue a task to fire a simple event that is cancelable called error at the ApplicationCache singleton of the Document for this entry, if there still is one. The default action of this event should be the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

    3. If this is a cache attempt and this entry is the last entry in cache group's list of pending master entries, then run these further substeps:

      1. Discard cache group and its only application cache, new cache.

      2. If appropriate, remove any user interface indicating that an update for this cache is in progress.

      3. Abort the update process.

    4. Otherwise, remove this entry from cache group's list of pending master entries.

    Otherwise, store the resource for this entry in new cache, if it isn't already there, and categorize its entry as a master entry.

  20. Fetch the resource from manifest URL again, and let second manifest be that resource.

  21. If the previous step failed for any reason, or if the fetching attempt involved a redirect, or if second manifest and manifest are not byte-for-byte identical, then schedule a rerun of the entire algorithm with the same parameters after a short delay, and run the cache failure steps.

  22. Otherwise, store manifest in new cache, if it's not there already, and categorize its entry as the manifest.

  23. Set the completeness flag of new cache to complete.

  24. If this is a cache attempt, then for each cache host associated with an application cache in cache group, queue a task to fire a simple event that is cancelable called cached at the ApplicationCache singleton of the cache host. The default action of these events should be the display of some sort of user interface indicating to the user that the application has been cached and that they can now use it offline.

    Otherwise, it is an upgrade attempt. For each cache host associated with an application cache in cache group, queue a task to fire a simple event that is cancelable called updateready at the ApplicationCache singleton of the cache host. The default action of these events should be the display of some sort of user interface indicating to the user that a new version is available and that they can activate it by reloading the page.

  25. If appropriate, remove any user interface indicating that an update for this cache is in progress.

  26. Set the update status of cache group to idle.

The cache failure steps are as follows:

  1. For each entry in cache group's list of pending master entries, run the following further substeps. These steps may be run in parallel for two or more entries at a time.

    1. Wait for the resource for this entry to have either completely downloaded or failed.

    2. Unassociate the Document for this entry from its application cache, if it has one.

    3. Queue a task to fire a simple event that is cancelable called error at the ApplicationCache singleton of the Document for this entry, if there still is one. The default action of these events should be the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

  2. For each cache host still associated with an application cache in cache group, queue a task to fire a simple event that is cancelable called error at the ApplicationCache singleton of the cache host. The default action of these events should be the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

  3. Empty cache group's list of pending master entries.

  4. If cache group has an application cache whose completeness flag is incomplete, then discard that application cache.

  5. If appropriate, remove any user interface indicating that an update for this cache is in progress.

  6. Let the status of cache group be idle.

  7. If this was a cache attempt, discard cache group altogether.

  8. Abort the update process.

Attempts to fetch resources as part of the application cache update process may be done with cache-defeating semantics, to avoid problems with stale or inconsistent intermediary caches.


User agents may invoke the application cache update process, in the background, for any application cache, at any time (with no cache host). This allows user agents to keep caches primed and to update caches even before the user visits a site.

5.8.5 Matching a fallback namespace

A URL matches a fallback namespace if there exists a relevant application cache whose manifest's URL has the same origin as the URL in question, and that has a fallback namespace that is a prefix match for the URL being examined. If multiple fallback namespaces match the same URL, the longest one is the one that matches. A URL looking for an fallback namespace can match more than one application cache at a time, but only matches one namespace in each cache.

If a manifest http://example.com/app1/manifest declares that http://example.com/resources/images is a fallback namespace, and the user navigates to HTTP://EXAMPLE.COM:80/resources/images/cat.png, then the user agent will decide that the application cache identified by http://example.com/app1/manifest contains a namespace with a match for that URL.

5.8.6 The application cache selection algorithm

When the application cache selection algorithm algorithm is invoked with a Document document and optionally a manifest URL manifest URL, the user agent must run the first applicable set of steps from the following list:

If there is a manifest URL, and document was loaded from an application cache, and the URL of the manifest of that cache's application cache group is not the same as manifest URL

Mark the entry for the resource from which document was taken in the application cache from which it was loaded as foreign.

Restart the current navigation from the top of the navigation algorithm, undoing any changes that were made as part of the initial load (changes can be avoided by ensuring that the step to update the session history with the new page is only ever completed after this application cache selection algorithm is run, though this is not required).

The navigation will not result in the same resource being loaded, because "foreign" entries are never picked during navigation.

User agents may notify the user of the inconsistency between the cache manifest and the document's own metadata, to aid in application development.

If document was loaded from an application cache

Associate document with the application cache from which it was loaded. Invoke the application cache update process for that cache and with the browsing context being navigated.

If document was loaded using HTTP GET or equivalent, and, there is a manifest URL, and manifest URL has the same origin as document

Invoke the application cache update process for manifest URL, with the browsing context being navigated, and with document and the resource from which document was loaded as the new master resource.

Otherwise

The Document is not associated with any application cache.

If there was a manifest URL, the user agent may report to the user that it was ignored, to aid in application development.

5.8.7 Changes to the networking model

When a cache host is associated with an application cache whose completeness flag is complete, any and all loads for resources related to that cache host other than those for child browsing contexts must go through the following steps instead of immediately invoking the mechanisms appropriate to that resource's scheme:

  1. If the resource is not to be fetched using the HTTP GET mechanism or equivalent, or if it has a javascript: URL, then fetch the resource normally and abort these steps.

  2. If the resource's URL is a master entry, the manifest, an explicit entry, or a fallback entry in the application cache, then get the resource from the cache (instead of fetching it), and abort these steps.

  3. If the resource's URL has the same origin as the manifest's URL, and there is a fallback namespace in the application cache that is a prefix match for the resource's URL, then:

    Fetch the resource normally. If this results in a redirect to a resource with another origin (indicative of a captive portal), or a 4xx or 5xx status code or equivalent, or if there were network errors (but not if the user canceled the download), then instead get, from the cache, the resource of the fallback entry corresponding to the matched namespace. Abort these steps.

  4. If there is an entry in the application cache's online whitelist that has the same origin as the resource's URL and that is a prefix match for the resource's URL, then fetch the resource normally and abort these steps.

  5. Fail the resource load.

The above algorithm ensures that resources that are not present in the manifest will always fail to load (at least, after the application cache has been primed the first time), making the testing of offline applications simpler.

5.8.8 Application cache API

interface ApplicationCache {

  // update status
  const unsigned short UNCACHED = 0;
  const unsigned short IDLE = 1;
  const unsigned short CHECKING = 2;
  const unsigned short DOWNLOADING = 3;
  const unsigned short UPDATEREADY = 4;
  const unsigned short OBSOLETE = 5;
  readonly attribute unsigned short status;

  // updates
  void update();
  void swapCache();

  // events
           attribute Function onchecking;
           attribute Function onerror;
           attribute Function onnoupdate;
           attribute Function ondownloading;
           attribute Function onprogress;
           attribute Function onupdateready;
           attribute Function oncached;
           attribute Function onobsolete;

};
cache = window . applicationCache

(In a window.) Returns the ApplicationCache object that applies to the active document of that Window.

cache = self . applicationCache

(In a shared worker.) Returns the ApplicationCache object that applies to the current shared worker.

cache . status

Returns the current status of the application cache, as given by the constants defined below.

cache . update()

Invokes the application cache update process.

Throws an INVALID_ACCESS_ERR exception if there is no application cache to update.

cache . swapCache()

Switches to the most recent application cache, if there is a newer one. If there isn't, throws an INVALID_ACCESS_ERR exception.

Objects implementing the ApplicationCache interface must also implement the EventTarget interface.

There is a one-to-one mapping from cache hosts to ApplicationCache objects. The applicationCache attribute on Window objects must return the ApplicationCache object associated with the Window object's active document. The applicationCache attribute on SharedWorkerGlobalScope objects must return the ApplicationCache object associated with the worker.

The status attribute, on getting, must return the current state of the application cache that the ApplicationCache object's cache host is associated with, if any. This must be the appropriate value from the following list:

UNCACHED (numeric value 0)

The ApplicationCache object's cache host is not associated with an application cache at this time.

IDLE (numeric value 1)

The ApplicationCache object's cache host is associated with an application cache whose application cache group's update status is idle, and that application cache is the newest cache in its application cache group, and the application cache group is not marked as obsolete.

CHECKING (numeric value 2)

The ApplicationCache object's cache host is associated with an application cache whose application cache group's update status is checking.

DOWNLOADING (numeric value 3)

The ApplicationCache object's cache host is associated with an application cache whose application cache group's update status is downloading.

UPDATEREADY (numeric value 4)

The ApplicationCache object's cache host is associated with an application cache whose application cache group's update status is idle, and whose application cache group is not marked as obsolete, but that application cache is not the newest cache in its group.

OBSOLETE (numeric value 5)

The ApplicationCache object's cache host is associated with an application cache whose application cache group is marked as obsolete.


If the update() method is invoked, the user agent must invoke the application cache update process, in the background, for the application cache with which the ApplicationCache object's cache host is associated, but without giving that cache host to the algorithm. If there is no such application cache, or if it is marked as obsolete, then the method must raise an INVALID_STATE_ERR exception instead.

If the swapCache() method is invoked, the user agent must run the following steps:

  1. Check that ApplicationCache object's cache host is associated with an application cache. If it is not, then raise an INVALID_STATE_ERR exception and abort these steps.

  2. Let cache be the application cache with which the ApplicationCache object's cache host is associated. (By definition, this is the same as the one that was found in the previous step.)

  3. If cache's application cache group is marked as obsolete, then unassociate the ApplicationCache object's cache host from cache and abort these steps. (Resources will now load from the network instead of the cache.)

  4. Check that there is an application cache in the same application cache group as cache whose completeness flag is complete and that is newer than cache. If there is not, then raise an INVALID_STATE_ERR exception and abort these steps.

  5. Let new cache be the newest application cache in the same application cache group as cache whose completeness flag is complete.

  6. Unassociate the ApplicationCache object's cache host from cache and instead associate it with new cache.

The following are the event handler attributes (and their corresponding event handler event types) that must be supported, as DOM attributes, by all objects implementing the ApplicationCache interface:

event handler attribute Event handler event type
onchecking checking
onerror error
onnoupdate noupdate
ondownloading downloading
onprogress progress
onupdateready updateready
oncached cached
onobsolete obsolete

5.8.9 Browser state

window . navigator . onLine

Returns false if the user agent is definitely offline (disconnected from the network). Returns true if the user agent might be online.

The navigator.onLine attribute must return false if the user agent will not contact the network when the user follows links or when a script requests a remote page (or knows that such an attempt would fail), and must return true otherwise.

When the value that would be returned by the navigator.onLine attribute of the Window changes from true to false, the user agent must fire a simple event called offline at the Window object.

On the other hand, when the value that would be returned by the navigator.onLine attribute of the Window changes from false to true, the user agent must fire a simple event called online at the Window object.

This attribute is inherently unreliable. A computer can be connected to a network without having Internet access.

5.9 Session history and navigation

5.9.1 The session history of browsing contexts

The sequence of Documents in a browsing context is its session history.

History objects provide a representation of the pages in the session history of browsing contexts. Each browsing context, including nested browsing context, has a distinct session history.

Each Document object in a browsing context's session history is associated with a unique instance of the History object, although they all must model the same underlying session history.

The history attribute of the Window interface must return the object implementing the History interface for that Window object's Document.

History objects represent their browsing context's session history as a flat list of session history entries. Each session history entry consists of either a URL or a state object, or both, and may in addition have a title, a Document object, form data, a scroll position, and other information associated with it.

This does not imply that the user interface need be linear. See the notes below.

URLs without associated state objects are added to the session history as the user (or script) navigates from page to page.

A state object is an object representing a user interface state.

Pages can add state objects between their entry in the session history and the next ("forward") entry. These are then returned to the script when the user (or script) goes back in the history, thus enabling authors to use the "navigation" metaphor even in one-page applications.

At any point, one of the entries in the session history is the current entry. This is the entry representing the active document of the browsing context. The current entry is usually an entry for the location of the Document. However, it can also be one of the entries for state objects added to the history by that document.

Entries that consist of state objects share the same Document as the entry for the page that was active when they were added.

Contiguous entries that differ just by fragment identifier also share the same Document.

All entries that share the same Document (and that are therefore merely different states of one particular document) are contiguous by definition.

User agents may discard the Document objects of entries other than the current entry that are not referenced from any script, reloading the pages afresh when the user or script navigates back to such pages. This specification does not specify when user agents should discard Document objects and when they should cache them.

Entries that have had their Document objects discarded must, for the purposes of the algorithms given below, act as if they had not. When the user or script navigates back or forwards to a page which has no in-memory DOM objects, any other entries that shared the same Document object with it must share the new object as well.

When state object entries are added, a URL can be provided. This URL is used to replace the state object entry if the Document is evicted.

5.9.2 The History interface

interface History {
  readonly attribute long length;
  void go([Optional] in long delta);
  void back();
  void forward();
  void pushState(in any data, in DOMString title, [Optional] in DOMString url);
  void clearState();
};
window . history . length

Returns the number of entries in the session history.

window . history . go( [ delta ] )

Goes back or forward the specified number of steps in the history.

A zero delta will reload the current page.

If the delta is out of range, does nothing.

window . history . back()

Goes back one step in the history.

If there is no previous page, does nothing.

window . history . forward()

Goes forward one step in the history.

If there is no next page, does nothing.

window . history . pushstate(data, title [, url ] )

Pushes the given data onto the session history, with the given title, and, if provided, the given URL.

window . history . clearState()

Removes all state objects for the current page from the session history.

The length attribute of the History interface must return the number of entries in this session history.

The actual entries are not accessible from script.

The go(delta) method causes the UA to move the number of steps specified by delta in the session history.

If the delta is zero, or if the argument is omitted, then the user agent must act as if the location.reload() method was called instead.

Otherwise, if the index of the current entry plus delta is less than zero or greater than or equal to the number of items in the session history, then the user agent must do nothing.

Otherwise, the user agent must cause the current browsing context to traverse the history to the specified entry. The specified entry is the one whose index equals the index of the current entry plus delta.

When the user navigates through a browsing context, e.g. using a browser's back and forward buttons, the user agent must translate this action into the equivalent invocations of the history.go(delta) method on the various affected window objects.

Some of the other members of the History interface are defined in terms of the go() method, as follows:

Member Definition
back() Must do the same as go(-1)
forward() Must do the same as go(1)

The pushState(data, title, url) method adds a state object to the history.

When this method is invoked, the user agent must run the following steps:

  1. Let clone data be a structured clone of the specified data. If this throws an exception, then rethrow that exception and abort these steps.

  2. If a third argument is specified, run these substeps:

    1. Resolve the value of the third argument, relative to the first script's base URL.
    2. If that fails, raise a SECURITY_ERR exception and abort the pushState() steps.
    3. Compare the resulting absolute URL to the document's address. If any part of these two URLs differ other than the <path>, <query>, and <fragment> components, then raise a SECURITY_ERR exception and abort the pushState() steps.

    For the purposes of the comparison in the above substeps, the <path> and <query> components can only be the same if the URLs use a hierarchical <scheme>.

  3. Remove from the session history any entries for the Document from the entry after the current entry up to the last entry in the session history that references the same Document object, if any. If the current entry is the last entry in the session history, or if there are no entries after the current entry that reference the same Document object, then no entries are removed.

  4. Add a state object entry to the session history, after the current entry, with cloned data as the state object, the given title as the title, and, if the third argument is present, the absolute URL that was found earlier in this algorithm as the URL of the entry.

  5. If the third argument is present, set the document's current address to the absolute URL that was found earlier in this algorithm.

  6. Update the current entry to be the this newly added entry.

The title is purely advisory. User agents might use the title in the user interface.

User agents may limit the number of state objects added to the session history per page. If a page hits the UA-defined limit, user agents must remove the entry immediately after the first entry for that Document object in the session history after having added the new entry. (Thus the state history acts as a FIFO buffer for eviction, but as a LIFO buffer for navigation.)

The clearState() method removes all the state objects for the Document object from the session history.

When this method is invoked, the user agent must remove from the session history all the entries from the first state object entry for that Document object up to the last entry that references that same Document object, if any.

Then, if the current entry was removed in the previous step, the current entry must be set to the last entry for that Document object in the session history.

5.9.3 Activating state object entries

When an entry in the session history is activated (which happens during session traversal, as described above), the user agent must run the following steps:

  1. If the entry is a state object entry, let state be a structured clone of that state object. Otherwise, let state be null.

  2. Run the appropriate according to the conditions described:

    If the current document readiness is set to the string "complete"

    Queue a task to fire a popstate event in no namespace on the Window object of the Document, using the PopStateEvent interface, with the state attribute set to the value of state. This event must bubble but not be cancelable and has no default action. The task source for this task is the DOM manipulation task source.

    Otherwise

    Let the Document's pending state object be state. (If there was already a pending state object, the previous one is discarded.)

    The event will then be fired just after the load event.

The pending state object must be initially null.


interface PopStateEvent : Event {
  readonly attribute any state;
  void initPopStateEvent(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in any stateArg);
  void initPopStateEventNS(in DOMString namespaceURIArg, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in any stateArg);
};
event . state

Returns the information that was provided to pushState().

The initPopStateEvent() and initPopStateEventNS() methods must initialize the event in a manner analogous to the similarly-named methods in the DOM3 Events interfaces. [DOM3EVENTS]

The state attribute represents the context information for the event, or null, if the state represented is the initial state of the Document.

5.9.4 The Location interface

Each Document object in a browsing context's session history is associated with a unique instance of a Location object.

document . location [ = value ]
window . location [ = value ]

Returns a Location object with the current page's location.

Can be set, to navigate to another page.

The location attribute of the HTMLDocument interface must return the Location object for that Document object, if it is in a browsing context, and null otherwise.

The location attribute of the Window interface must return the Location object for that Window object's Document.

Location objects provide a representation of their document's current address, and allow the current entry of the browsing context's session history to be changed, by adding or replacing entries in the history object.

interface Location {
  readonly attribute DOMString href;
  void assign(in DOMString url);
  void replace(in DOMString url);
  void reload();

  // URL decomposition attributes 
           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;

  // resolving relative URLs
  DOMString resolveURL(in DOMString url);
};
location . href [ = value ]

Returns the current page's location.

Can be set, to navigate to another page.

location . assign(url)

Navigates to the given page.

location . replace(url)

Removes the current page from the session history and navigates to the given page.

location . reload()

Reloads the current page.

url = location . resolveURL(url)

Resolves the given relative URL to an absolute URL.

The href attribute must return the current address of the associated Document object, as an absolute URL.

On setting, the user agent must act as if the assign() method had been called with the new value as its argument.

When the assign(url) method is invoked, the UA must resolve the argument, relative to the first script's base URL, and if that is successful, must navigate the browsing context to the specified url.

When the replace(url) method is invoked, the UA must resolve the argument, relative to the first script's base URL, and if that is successful, navigate the browsing context to the specified url with replacement enabled.

Navigation for the assign() and replace() methods must be done with the browsing context of the script that invoked the method as the source browsing context.

If the resolving step of the assign() and replace() methods is not successful, then the user agent must instead throw a SYNTAX_ERR exception.

The Location interface also has the complement of URL decomposition attributes, protocol, host, port, hostname, pathname, search, and hash. These must follow the rules given for URL decomposition attributes, with the input being the current address of the associated Document object, as an absolute URL (same as the href attribute), and the common setter action being the same as setting the href attribute to the new output value.


The resolveURL(url) method must resolve its url argument, relative to the first script's base URL, and if that succeeds, return the resulting absolute URL. If it fails, it must throw a SYNTAX_ERR exception instead.

5.9.4.1 Security

User agents must raise a SECURITY_ERR exception whenever any of the members of a Location object are accessed by scripts whose effective script origin is not the same as the Location object's associated Document's effective script origin, with the following exceptions:

User agents must not allow scripts to override the href attribute's setter.

5.9.5 Implementation notes for session history

This section is non-normative.

The History interface is not meant to place restrictions on how implementations represent the session history to the user.

For example, session history could be implemented in a tree-like manner, with each page having multiple "forward" pages. This specification doesn't define how the linear list of pages in the history object are derived from the actual session history as seen from the user's perspective.

Similarly, a page containing two iframes has a history object distinct from the iframes' history objects, despite the fact that typical Web browsers present the user with just one "Back" button, with a session history that interleaves the navigation of the two inner frames and the outer page.

Security: It is suggested that to avoid letting a page "hijack" the history navigation facilities of a UA by abusing pushState(), the UA provide the user with a way to jump back to the previous page (rather than just going back to the previous state). For example, the back button could have a drop down showing just the pages in the session history, and not showing any of the states. Similarly, an aural browser could have two "back" commands, one that goes back to the previous state, and one that jumps straight back to the previous page.

In addition, a user agent could ignore calls to pushState() that are invoked on a timer, or from event handlers that do not represent a clear user action, or that are invoked in rapid succession.

5.10 Browsing the Web

Certain actions cause the browsing context to navigate to a new resource. Navigation always involves source browsing context, which is the browsing context which was responsible for starting the navigation.

For example, following a hyperlink, form submission, and the window.open() and location.assign() methods can all cause a browsing context to navigate.

A user agent may provide various ways for the user to explicitly cause a browsing context to navigate, in addition to those defined in this specification.

When a browsing context is navigated to a new resource, the user agent must run the following steps:

  1. Cancel any preexisting attempt to navigate the browsing context.

  2. If the new resource is to be handled by displaying some sort of inline content, e.g. an error message because the specified scheme is not one of the supported protocols, or an inline prompt to allow the user to select a registered handler for the given scheme, then display the inline content and abort these steps.

  3. If the new resource is to be handled using a mechanism that does not affect the browsing context, e.g. ignoring the navigation request altogether because the specified scheme is not one of the supported protocols, then abort these steps and proceed with that mechanism instead.

  4. If the new resource is to be fetched using HTTP GET or equivalent, then check if there are any relevant application caches that are identified by a URL with the same origin as the URL in question, and that have this URL as one of their entries, excluding entries marked as foreign. If so, then the user agent must then get the resource from the most appropriate application cache of those that match.

    For example, imagine an HTML page with an associated application cache displaying an image and a form, where the image is also used by several other application caches. If the user right-clicks on the image and chooses "View Image", then the user agent could decide to show the image from any of those caches, but it is likely that the most useful cache for the user would be the one that was used for the aforementioned HTML page. On the other hand, if the user submits the form, and the form does a POST submission, then the user agent will not use an application cache at all; the submission will be made to the network.

    Otherwise, fetch the new resource, if it has not already been obtained. If the resource is being fetched using HTTP, and the method is not GET, then the user agent must include an XXX-Origin header whose value is determined as follows:

    If the navigation algorithm has so far contacted more than one origin
    If there is no source browsing context
    The value must be the string "null".
    Otherwise
    The value must be the ASCII serialization of the origin of the active document of the source browsing context at the time the navigation was started.
  5. If fetching the resource is synchronous (i.e. for javascript: URLs and about:blank), then this must be synchronous, but if fetching the resource depends on external resources, as it usually does for URLs that use HTTP or other networking protocols, then at this point the user agents must yield to whatever script invoked the navigation steps, if they were invoked by script.

  6. If fetching the resource results in a redirect, return to the step labeled "fragment identifiers" with the new resource.

    Cross-origin redirects cause the XXX-Origin header to become "null" on subsequent requests in the chain.

  7. Wait for one or more bytes to be available or for the user agent to establish that the resource in question is empty. During this time, the user agent may allow the user to cancel this navigation attempt or start other navigation attempts.

  8. If the resource was not fetched from an application cache, and was to be fetched using HTTP GET or equivalent, and its URL matches the fallback namespace of one or more relevant application caches, and the user didn't cancel the navigation attempt during the previous step, and the navigation attempt failed (e.g. the server returned a 4xx or 5xx status code or equivalent, or there was a DNS error), then:

    Let candidate be the fallback resource specified for the fallback namespace in question. If multiple application caches match, the user agent must use the fallback of the most appropriate application cache of those that match.

    If candidate is not marked as foreign, then the user agent must discard the failed load and instead continue along these steps using candidate as the resource. The document's address, if appropriate, will still be the originally requested URL, not the fallback URL, but the user agent may indicate to the user that the original page load failed, that the page used was a fallback resource, and what the URL of the fallback resource actually is.

  9. If the document's out-of-band metadata (e.g. HTTP headers), not counting any type information (such as the Content-Type HTTP header), requires some sort of processing that will not affect the browsing context, then perform that processing and abort these steps.

    Such processing might be triggered by, amongst other things, the following:

    • HTTP status codes (e.g. 204 No Content or 205 Reset Content)
    • HTTP Content-Disposition headers
    • Network errors

    HTTP 401 responses that do not include a challenge recognized by the user agent must be processed as if they had no challenge, e.g. rendering the entity body as if the response had been 200 OK.

    User agents may show the entity body of an HTTP 401 response even when the response do include a recognized challenge, with the option to login being included in a non-modal fashion, to enable the information provided by the server to be used by the user before authenticating. Similarly, user agents should allow the user to authenticate (in a non-modal fashion) against authentication challenges included in other responses such as HTTP 200 OK responses, effectively allowing resources to present HTTP login forms without requiring their use.

  10. Let type be the sniffed type of the resource.

  11. If the user agent has been configured to process resources of the given type using some mechanism other than rendering the content in a browsing context, then skip this step. Otherwise, if the type is one of the following types, jump to the appropriate entry in the following list, and process the resource as described there:

    "text/html"
    Follow the steps given in the HTML document section, and abort these steps.
    Any type ending in "+xml"
    "application/xml"
    "text/xml"
    Follow the steps given in the XML document section. If that section determines that the content is not to be displayed as a generic XML document, then proceed to the next step in this overall set of steps. Otherwise, abort these steps.
    "text/plain"
    Follow the steps given in the plain text file section, and abort these steps.
    A supported image type
    Follow the steps given in the image section, and abort these steps.
    A type that will use an external application to render the content in the browsing context
    Follow the steps given in the plugin section, and abort these steps.

    Setting the document's address: If there is no override URL, then any Document created by these steps must have its address set to the URL that was originally to be fetched, ignoring any other data that was used to obtain the resource (e.g. the entity body in the case of a POST submission is not part of the document's address, nor is the URL of the fallback resource in the case of the original load having failed and that URL having been found to match a fallback namespace). However, if there is an override URL, then any Document created by these steps must have its address set to that URL instead.

    An override URL is set when dereferencing a javascript: URL.

  12. Otherwise, the document's type is such that the resource will not affect the browsing context, e.g. because the resource is to be handed to an external application. Process the resource appropriately.

Some of the sections below, to which the above algorithm defers in certain cases, require the user agent to update the session history with the new page. When a user agent is required to do this, it must queue a task to run the following steps:

  1. Unload the Document object of the current entry, with the recycle parameter set to false.

  2. If the navigation was initiated for entry update of an entry
    1. Replace the entry being updated with a new entry representing the new resource and its Document object and related state. The user agent may propagate state from the old entry to the new entry (e.g. scroll position).

    2. Traverse the history to the new entry.

    Otherwise
    1. Remove all the entries after the current entry in the browsing context's Document object's History object.

      This doesn't necessarily have to affect the user agent's user interface.

    2. Append a new entry at the end of the History object representing the new resource and its Document object and related state.

    3. Traverse the history to the new entry.

    4. If the navigation was initiated with replacement enabled, remove the entry immediately before the new current entry in the session history.

  3. If the document's address has a fragment identifier, then run these substeps:

    1. Wait for a user-agent defined amount of time, as desired by the user agent implementor. (This is intended to allow the user agent to optimize the user experience in the face of performance concerns.)

    2. If the Document object has no parser, or its parser has stopped parsing, or the user agent has reason to believe the user is no longer interested in scrolling to the fragment identifier, then abort these substeps.

    3. Scroll to the fragment identifier given in the document's current address. If this fails to find an indicated part of the document, then return to the first step of these substeps.

The task source for this task is the networking task source.

5.10.2 Page load processing model for HTML files

When an HTML document is to be loaded in a browsing context, the user agent must create a Document object, mark it as being an HTML document, create an HTML parser, associate it with the document, and begin to use the bytes provided for the document as the input stream for that parser.

The input stream converts bytes into characters for use in the tokenizer. This process relies, in part, on character encoding information found in the real Content-Type metadata of the resource; the "sniffed type" is not used for this purpose.

When no more bytes are available, an EOF character is implied, which eventually causes a load event to be fired.

After creating the Document object, but potentially before the page has finished parsing, the user agent must update the session history with the new page.

Application cache selection happens in the HTML parser.

5.10.3 Page load processing model for XML files

When faced with displaying an XML file inline, user agents must first create a Document object, following the requirements of the XML and Namespaces in XML recommendations, RFC 3023, DOM3 Core, and other relevant specifications. [XML] [XMLNS] [RFC3023] [DOM3CORE]

The actual HTTP headers and other metadata, not the headers as mutated or implied by the algorithms given in this specification, are the ones that must be used when determining the character encoding according to the rules given in the above specifications. Once the character encoding is established, the document's character encoding must be set to that character encoding.

If the root element, as parsed according to the XML specifications cited above, is found to be an html element with an attribute manifest, then, as soon as the element is inserted into the document, the user agent must resolve the value of that attribute relative to that element, and if that is successful, must run the application cache selection algorithm with the resulting absolute URL as the manifest URL, and passing in the newly-created Document. Otherwise, if the attribute is absent or resolving it fails, then as soon as the root element is inserted into the document, the user agent must run the application cache selection algorithm with no manifest, and passing in the Document.

Because the processing of the manifest attribute happens only once the root element is parsed, any URLs referenced by processing instructions before the root element (such as <?xml-stylesheet?> and <?xbl?> PIs) will be fetched from the network and cannot be cached.

User agents may examine the namespace of the root Element node of this Document object to perform namespace-based dispatch to alternative processing tools, e.g. determining that the content is actually a syndication feed and passing it to a feed handler. If such processing is to take place, abort the steps in this section, and jump to the next step (labeled "non-document content") in the navigate steps above.

Otherwise, then, with the newly created Document, the user agents must update the session history with the new page. User agents may do this before the complete document has been parsed (thus achieving incremental rendering).

Error messages from the parse process (e.g. XML namespace well-formedness errors) may be reported inline by mutating the Document.

5.10.4 Page load processing model for text files

When a plain text document is to be loaded in a browsing context, the user agent should create a Document object, mark it as being an HTML document, create an HTML parser, associate it with the document, act as if the tokenizer had emitted a start tag token with the tag name "pre", set the tokenization stage's content model flag to PLAINTEXT, and begin to pass the stream of characters in the plain text document to that tokenizer.

The rules for how to convert the bytes of the plain text document into actual characters are defined in RFC 2046, RFC 2646, and subsequent versions thereof. [RFC2046] [RFC2646]

The document's character encoding must be set to the character encoding used to decode the document.

Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and passing in the newly-created Document.

When no more character are available, an EOF character is implied, which eventually causes a load event to be fired.

After creating the Document object, but potentially before the page has finished parsing, the user agent must update the session history with the new page.

User agents may add content to the head element of the Document, e.g. linking to stylesheet or an XBL binding, providing script, giving the document a title, etc.

5.10.5 Page load processing model for images

When an image resource is to be loaded in a browsing context, the user agent should create a Document object, mark it as being an HTML document, append an html element to the Document, append a head element and a body element to the html element, append an img to the body element, and set the src attribute of the img element to the address of the image.

Then, the user agent must act as if it had stopped parsing.

Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and passing in the newly-created Document.

After creating the Document object, but potentially before the page has finished fully loading, the user agent must update the session history with the new page.

User agents may add content to the head element of the Document, or attributes to the img element, e.g. to link to stylesheet or an XBL binding, to provide a script, to give the document a title, etc.

5.10.6 Page load processing model for content that uses plugins

When a resource that requires an external resource to be rendered is to be loaded in a browsing context, the user agent should create a Document object, mark it as being an HTML document, append an html element to the Document, append a head element and a body element to the html element, append an embed to the body element, and set the src attribute of the embed element to the address of the resource.

Then, the user agent must act as if it had stopped parsing.

Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and passing in the newly-created Document.

After creating the Document object, but potentially before the page has finished fully loading, the user agent must update the session history with the new page.

User agents may add content to the head element of the Document, or attributes to the embed element, e.g. to link to stylesheet or an XBL binding, or to give the document a title.

If the sandboxed plugins browsing context flag is set on the browsing context, the synthesized embed element will fail to render the content.

5.10.7 Page load processing model for inline content that doesn't have a DOM

When the user agent is to display a user agent page inline in a browsing context, the user agent should create a Document object, mark it as being an HTML document, and then either associate that Document with a custom rendering that is not rendered using the normal Document rendering rules, or mutate that Document until it represents the content the user agent wants to render.

Once the page has been set up, the user agent must act as if it had stopped parsing.

Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, passing in the newly-created Document.

After creating the Document object, but potentially before the page has been completely set up, the user agent must update the session history with the new page.

5.10.8 Navigating to a fragment identifier

When a user agent is supposed to navigate to a fragment identifier, then the user agent must queue a task to run the following steps:

  1. Remove all the entries after the current entry in the browsing context's Document object's History object.

    This doesn't necessarily have to affect the user agent's user interface.

  2. Append a new entry at the end of the History object representing the new resource and its Document object and related state, and set its URL to the address to which the user agent was navigating. (This will be the same as the document's address, but with a new fragment identifier.)

  3. Traverse the history to the new entry. This will scroll to the fragment identifier given in the document's current address.


When the user agent is required to scroll to the fragment identifier, it must change the scrolling position of the document, or perform some other action, such that the indicated part of the document is brought to the user's attention. If there is no indicated part, then the user agent must not scroll anywhere.

The indicated part of the document is the one that the fragment identifier, if any, identifies. The semantics of the fragment identifier in terms of mapping it to a specific DOM Node is defined by the MIME type specification of the document's MIME Type (for example, the processing of fragment identifiers for XML MIME types is the responsibility of RFC3023).

For HTML documents (and the text/html MIME type), the following processing model must be followed to determine what the indicated part of the document is.

  1. Parse the URL, and let fragid be the <fragment> component of the URL.

  2. If fragid is the empty string, then the indicated part of the document is the top of the document.

  3. Let decoded fragid be the result of expanding any sequences of percent-encoded octets in fragid that are valid UTF-8 sequences into Unicode characters as defined by UTF-8. If any percent-encoded octets in that string are not valid UTF-8 sequences, then skip this step and the next one.

  4. If this step was not skipped and there is an element in the DOM that has an ID exactly equal to decoded fragid, then the first such element in tree order is the indicated part of the document; stop the algorithm here.

  5. If there is an a element in the DOM that has a name attribute whose value is exactly equal to fragid (not decoded fragid), then the first such element in tree order is the indicated part of the document; stop the algorithm here.

  6. Otherwise, there is no indicated part of the document.

For the purposes of the interaction of HTML with Selectors' :target pseudo-class, the target element is the indicated part of the document, if that is an element; otherwise there is no target element. [SELECTORS]

5.10.9 History traversal

When a user agent is required to traverse the history to a specified entry, the user agent must act as follows:

  1. If there is no longer a Document object for the entry in question, the user agent must navigate the browsing context to the location for that entry to perform an entry update of that entry, and abort these steps. The "navigate" algorithm reinvokes this "traverse" algorithm to complete the traversal, at which point there is a Document object and so this step gets skipped. The navigation must be done using the same source browsing context as was used the first time this entry was created.

  2. If appropriate, update the current entry in the browsing context's Document object's History object to reflect any state that the user agent wishes to persist.

    For example, some user agents might want to persist the scroll position, or the values of form controls.

  3. If the specified entry has a different Document object than the current entry then the user agent must run the following substeps:

    1. If the browsing context is a top-level browsing context (and not an auxiliary browsing context), and the origin of the Document of the specified entry is not the same as the origin of the Document of the current entry, then the following sub-sub-steps must be run:
      1. The current browsing context name must be stored with all the entries in the history that are associated with Document objects with the same origin as the active document and that are contiguous with the current entry.
      2. The browsing context's browsing context name must be unset.
    2. The user agent must make the specified entry's Document object the active document of the browsing context.
    3. If the specified entry has a browsing context name stored with it, then the following sub-sub-steps must be run:
      1. The browsing context's browsing context name must be set to the name stored with the specified entry.
      2. Any browsing context name stored with the entries in the history that are associated with Document objects with the same origin as the new active document, and that are contiguous with the specified entry, must be cleared.
  4. Set the document's current address to the URL of the specified entry.

  5. If the specified entry is a state object or the first entry for a Document, the user agent must activate that entry.

  6. If the specified entry has a URL that differs from the current entry's only by its fragment identifier, and the two share the same Document object, then first, if the Document's current document readiness is the string "complete", then fire a simple event with the name hashchange at the browsing context's Window object; and second, if the new URL has a fragment identifier, scroll to the fragment identifier.

  7. User agents may also update other aspects of the document view when the location changes in this way, for instance the scroll position, values of form fields, etc.

  8. The current entry is now the specified entry.

5.10.10 Unloading documents

When a user agent is to unload a document, it must run the following steps. These steps are passed an argument, recycle, which is either true or false, indicating whether the Document object is going to be re-used. (This is set by the document.open() method.)

  1. Set salvageable to true.

  2. Let event be a new BeforeUnloadEvent event object with the name beforeunload, with no namespace, which does not bubble but is cancelable.

  3. Dispatch event at the Document's Window object.

  4. If any event listeners were triggered by the previous step, then set salvageable to false.

  5. If the returnValue attribute of the event object is not the empty string, or if the event was canceled, then the user agent should ask the user to confirm that they wish to unload the document.

    The prompt shown by the user agent may include the string of the returnValue attribute, or some leading subset thereof. (A user agent may want to truncate the string to 1024 characters for display, for instance.)

    The user agent must pause while waiting for the user's response.

    If the user refused to allow the document to be unloaded then these steps must be aborted.

  6. Fire a simple event called unload at the Document's Window object.

  7. If any event listeners were triggered by the previous step, then set salvageable to false.

  8. If there are any outstanding transactions that have callbacks that involve scripts whose global object is the Document's Window object, roll them back (without invoking any of the callbacks) and set salvageable to false.

  9. If salvageable and recycle are both false, discard the Document.

5.10.10.1 Event definition
interface BeforeUnloadEvent : Event {
           attribute DOMString returnValue;
};
event . returnValue [ = value ]

Returns the current return value of the event (the message to show the user).

Can be set, to update the message.

There are no BeforeUnloadEvent-specific initialization methods.

The returnValue attribute represents the message to show the user. When the event is created, the attribute must be set to the empty string. On getting, it must return the last value it was set to. On setting, the attribute must be set to the new value.

The a, area, and link elements can, in certain situations described in the definitions of those elements, represent hyperlinks.

The href attribute on a hyperlink element must have a value that is a valid URL. This URL is the destination resource of the hyperlink.

The href attribute on a and area elements is not required; when those elements do not have href attributes they do not represent hyperlinks.

The href attribute on the link element is required, but whether a link element represents a hyperlink or not depends on the value of the rel attribute of that element.

The target attribute, if present, must be a valid browsing context name or keyword. It gives the name of the browsing context that will be used. User agents use this name when following hyperlinks.

The ping attribute, if present, gives the URLs of the resources that are interested in being notified if the user follows the hyperlink. The value must be a space separated list of one or more valid URLs. The value is used by the user agent for hyperlink auditing.

For a and area elements that represent hyperlinks, the relationship between the document containing the hyperlink and the destination resource indicated by the hyperlink is given by the value of the element's rel attribute, which must be a set of space-separated tokens. The allowed values and their meanings are defined below. The rel attribute has no default value. If the attribute is omitted or if none of the values in the attribute are recognized by the user agent, then the document has no particular relationship with the destination resource other than there being a hyperlink between the two.

The media attribute describes for which media the target document was designed. It is purely advisory. The value must be a valid media query. [MQ] The default, if the media attribute is omitted, is all.

The hreflang attribute on hyperlink elements, if present, gives the language of the linked resource. It is purely advisory. The value must be a valid RFC 3066 language code. [RFC3066] User agents must not consider this attribute authoritative — upon fetching the resource, user agents must use only language information associated with the resource to determine its language, not metadata included in the link to the resource.

The type attribute, if present, gives the MIME type of the linked resource. It is purely advisory. The value must be a valid MIME type, optionally with parameters. [RFC2046] User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use metadata included in the link to the resource to determine its type.

When a user follows a hyperlink, the user agent must resolve the URL given by the href attribute of that hyperlink, relative to the hyperlink element, and if that is successful, must navigate a browsing context to the resulting absolute URL. In the case of server-side image maps, the URL of the hyperlink must further have its hyperlink suffix appended to it.

If resolving the URL fails, the user agent may report the error to the user in a user-agent-specific manner, may navigate to an error page to report the error, or may ignore the error and do nothing.

If the user indicated a specific browsing context when following the hyperlink, or if the user agent is configured to follow hyperlinks by navigating a particular browsing context, then that must be the browsing context that is navigated.

Otherwise, if the hyperlink element is an a or area element that has a target attribute, then the browsing context that is navigated must be chosen by applying the rules for choosing a browsing context given a browsing context name, using the value of the target attribute as the browsing context name. If these rules result in the creation of a new browsing context, it must be navigated with replacement enabled.

Otherwise, if the hyperlink element is a sidebar hyperlink and the user agent implements a feature that can be considered a secondary browsing context, such a secondary browsing context may be selected as the browsing context to be navigated.

Otherwise, if the hyperlink element is an a or area element with no target attribute, but one of the child nodes of the head element is a base element with a target attribute, then the browsing context that is navigated must be chosen by applying the rules for choosing a browsing context given a browsing context name, using the value of the target attribute of the first such base element as the browsing context name. If these rules result in the creation of a new browsing context, it must be navigated with replacement enabled.

Otherwise, the browsing context that must be navigated is the same browsing context as the one which the hyperlink element itself is in.

The navigation must be done with the browsing context that contains the Document object with which the hyperlink's element in question is associated as the source browsing context.

If an a or area hyperlink element has a ping attribute, and the user follows the hyperlink, and the hyperlink's URL can be resolved, relative to the hyperlink element, without failure, then the user agent must take the ping attribute's value, split that string on spaces, resolve each resulting token relative to the hyperlink element, and then should send a request (as described below) to each of the resulting absolute URLs. (Tokens that fail to resolve are ignored.) This may be done in parallel with the primary request, and is independent of the result of that request.

User agents should allow the user to adjust this behavior, for example in conjunction with a setting that disables the sending of HTTP Referer (sic) headers. Based on the user's preferences, UAs may either ignore the ping attribute altogether, or selectively ignore URLs in the list (e.g. ignoring any third-party URLs).

For URLs that are HTTP URLs, the requests must be performed by fetching the specified URLs using the POST method, with an entity body with the MIME type text/ping consisting of the four-character string "PING". All relevant cookie and HTTP authentication headers must be included in the request. Which other headers are required depends on the URLs involved.

If both the address of the Document object containing the hyperlink being audited and the ping URL have the same origin
The request must include a Ping-From HTTP header with, as its value, the address of the document containing the hyperlink, and a Ping-To HTTP header with, as its value, the address of the absolute URL of the target of the hyperlink. The request must not include a Referer (sic) HTTP header.
Otherwise, if the origins are different, but the document containing the hyperlink being audited was not retrieved over an encrypted connection
The request must include a Referer (sic) HTTP header [sic] with, as its value, the current address of the document containing the hyperlink, a Ping-From HTTP header with the same value, and a Ping-To HTTP header with, as its value, the address of the target of the hyperlink.
Otherwise, the origins are different and the document containing the hyperlink being audited was retrieved over an encrypted connection
The request must include a Ping-To HTTP header with, as its value, the address of the target of the hyperlink. The request must neither include a Referer (sic) HTTP header nor include a Ping-From HTTP header.

In addition, an XXX-Origin header must always be included, whose value is the ASCII serialization of the origin of the Document containing the hyperlink. The value of the XXX-Origin header must be set to "null" when following redirects if the origins of all the URLs involved are not the same.

To save bandwidth, implementors might also wish to consider omitting optional headers such as Accept from these requests.

User agents must, unless otherwise specified by the user, honor the HTTP headers (including, in particular, redirects and HTTP cookie headers), but must ignore any entity bodies returned in the responses. User agents may close the connection prematurely once they start receiving an entity body. [RFC2109] [RFC2965]

For URLs that are not HTTP URLs, the requests must be performed by fetching the specified URL normally, and discarding the results.

When the ping attribute is present, user agents should clearly indicate to the user that following the hyperlink will also cause secondary requests to be sent in the background, possibly including listing the actual target URLs.

For example, a visual user agent could include the hostnames of the target ping URLs along with the hyperlink's actual URL in a status bar or tooltip.

The ping attribute is redundant with pre-existing technologies like HTTP redirects and JavaScript in allowing Web pages to track which off-site links are most popular or allowing advertisers to track click-through rates.

However, the ping attribute provides these advantages to the user over those alternatives:

Thus, while it is possible to track users without this feature, authors are encouraged to use the ping attribute so that the user agent can improve the user experience.

5.11.3 Link types

The following table summarizes the link types that are defined by this specification. This table is non-normative; the actual definitions for the link types are given in the next few sections.

In this section, the term referenced document refers to the resource identified by the element representing the link, and the term current document refers to the resource within which the element representing the link finds itself.

To determine which link types apply to a link, a, or area element, the element's rel attribute must be split on spaces. The resulting tokens are the link types that apply to that element.

Unless otherwise specified, a keyword must not be specified more than once per rel attribute.

The link types are ASCII case-insensitive values, and must be compared as such.

Thus, rel="next" is the same as rel="NEXT".

Link type Effect on... Brief description
link a and area
alternate Hyperlink Hyperlink Gives alternate representations of the current document.
archives Hyperlink Hyperlink Provides a link to a collection of records, documents, or other materials of historical interest.
author Hyperlink Hyperlink Gives a link to the current document's author.
bookmark not allowed Hyperlink Gives the permalink for the nearest ancestor section.
external not allowed Hyperlink Indicates that the referenced document is not part of the same site as the current document.
feed Hyperlink Hyperlink Gives the address of a syndication feed for the current document.
first Hyperlink Hyperlink Indicates that the current document is a part of a series, and that the first document in the series is the referenced document.
help Hyperlink Hyperlink Provides a link to context-sensitive help.
icon External Resource not allowed Imports an icon to represent the current document.
index Hyperlink Hyperlink Gives a link to the document that provides a table of contents or index listing the current document.
last Hyperlink Hyperlink Indicates that the current document is a part of a series, and that the last document in the series is the referenced document.
license Hyperlink Hyperlink Indicates that the current document is covered by the copyright license described by the referenced document.
next Hyperlink Hyperlink Indicates that the current document is a part of a series, and that the next document in the series is the referenced document.
nofollow not allowed Hyperlink Indicates that the current document's original author or publisher does not endorse the referenced document.
noreferrer not allowed Hyperlink Requires that the user agent not send an HTTP Referer (sic) header if the user follows the hyperlink.
pingback External Resource not allowed Gives the address of the pingback server that handles pingbacks to the current document.
prefetch External Resource not allowed Specifies that the target resource should be preemptively cached.
prev Hyperlink Hyperlink Indicates that the current document is a part of a series, and that the previous document in the series is the referenced document.
search Hyperlink Hyperlink Gives a link to a resource that can be used to search through the current document and its related pages.
stylesheet External Resource not allowed Imports a stylesheet.
sidebar Hyperlink Hyperlink Specifies that the referenced document, if retrieved, is intended to be shown in the browser's sidebar (if it has one).
tag Hyperlink Hyperlink Gives a tag (identified by the given address) that applies to the current document.
up Hyperlink Hyperlink Provides a link to a document giving the context for the current document.

Some of the types described below list synonyms for these values. These are to be handled as specified by user agents, but must not be used in documents.

The alternate keyword may be used with link, a, and area elements. For link elements, if the rel attribute does not also contain the keyword stylesheet, it creates a hyperlink; but if it does also contain the keyword stylesheet, the alternate keyword instead modifies the meaning of the stylesheet keyword in the way described for that keyword, and the rest of this subsection doesn't apply.

The alternate keyword indicates that the referenced document is an alternate representation of the current document.

The nature of the referenced document is given by the media, hreflang, and type attributes.

If the alternate keyword is used with the media attribute, it indicates that the referenced document is intended for use with the media specified.

If the alternate keyword is used with the hreflang attribute, and that attribute's value differs from the root element's language, it indicates that the referenced document is a translation.

If the alternate keyword is used with the type attribute, it indicates that the referenced document is a reformulation of the current document in the specified format.

The media, hreflang, and type attributes can be combined when specified with the alternate keyword.

For example, the following link is a French translation that uses the PDF format:

<link rel=alternate type=application/pdf hreflang=fr href=manual-fr>

If the alternate keyword is used with the type attribute set to the value application/rss+xml or the value application/atom+xml, then the user agent must treat the link as it would if it had the feed keyword specified as well.

The alternate link relationship is transitive — that is, if a document links to two other documents with the link type "alternate", then, in addition to implying that those documents are alternative representations of the first document, it is also implying that those two documents are alternative representations of each other.

The archives keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The archives keyword indicates that the referenced document describes a collection of records, documents, or other materials of historical interest.

A blog's index page could link to an index of the blog's past posts with rel="archives".

Synonyms: For historical reasons, user agents must also treat the keyword "archive" like the archives keyword.

The author keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

For a and area elements, the author keyword indicates that the referenced document provides further information about the author of the section that the element defining the hyperlink applies to.

For link elements, the author keyword indicates that the referenced document provides further information about the author for the page as a whole.

The "referenced document" can be, and often is, a mailto: URL giving the e-mail address of the author. [MAILTO]

Synonyms: For historical reasons, user agents must also treat link, a, and area elements that have a rev attribute with the value "made" as having the author keyword specified as a link relationship.

The bookmark keyword may be used with a and area elements.

The bookmark keyword gives a permalink for the nearest ancestor article element of the linking element in question, or of the section the linking element is most closely associated with, if there are no ancestor article elements.

The following snippet has three permalinks. A user agent could determine which permalink applies to which part of the spec by looking at where the permalinks are given.

 ...
 <body>
  <h1>Example of permalinks</h1>
  <div id="a">
   <h2>First example</h2>
   <p><a href="a.html" rel="bookmark">This</a> permalink applies to
   only the content from the first H2 to the second H2. The DIV isn't
   exactly that section, but it roughly corresponds to it.</p>
  </div>
  <h2>Second example</h2>
  <article id="b">
   <p><a href="b.html" rel="bookmark">This</a> permalink applies to
   the outer ARTICLE element (which could be, e.g., a blog post).</p>
   <article id="c">
    <p><a href="c.html" rel="bookmark">This</a> permalink applies to
    the inner ARTICLE element (which could be, e.g., a blog comment).</p>
   </article>
  </article>
 </body>
 ...

The external keyword may be used with a and area elements.

The external keyword indicates that the link is leading to a document that is not part of the site that the current document forms a part of.

The feed keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The feed keyword indicates that the referenced document is a syndication feed. If the alternate link type is also specified, then the feed is specifically the feed for the current document; otherwise, the feed is just a syndication feed, not necessarily associated with a particular Web page.

The first link, a, or area element in the document (in tree order) that creates a hyperlink with the link type feed must be treated as the default syndication feed for the purposes of feed autodiscovery.

The feed keyword is implied by the alternate link type in certain cases (q.v.).

The following two link elements are equivalent: both give the syndication feed for the current page:

<link rel="alternate" type="application/atom+xml" href="data.xml">
<link rel="feed alternate" href="data.xml">

The following extract offers various different syndication feeds:

 <p>You can access the planets database using Atom feeds:</p>
 <ul>
  <li><a href="recently-visited-planets.xml" rel="feed">Recently Visited Planets</a></li>
  <li><a href="known-bad-planets.xml" rel="feed">Known Bad Planets</a></li>
  <li><a href="unexplored-planets.xml" rel="feed">Unexplored Planets</a></li>
 </ul>

The help keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

For a and area elements, the help keyword indicates that the referenced document provides further help information for the parent of the element defining the hyperlink, and its children.

In the following example, the form control has associated context-sensitive help. The user agent could use this information, for example, displaying the referenced document if the user presses the "Help" or "F1" key.

 <p><label> Topic: <input name=topic> <a href="help/topic.html" rel="help">(Help)</a></label></p>

For link elements, the help keyword indicates that the referenced document provides help for the page as a whole.

5.11.3.8 Link type "icon"

The icon keyword may be used with link elements, for which it creates an external resource link.

The specified resource is an icon representing the page or site, and should be used by the user agent when representing the page in the user interface.

Icons could be auditory icons, visual icons, or other kinds of icons. If multiple icons are provided, the user agent must select the most appropriate icon according to the type, media, and sizes attributes. If there are multiple equally appropriate icons, user agents must use the last one declared in tree order. If the user agent tries to use an icon but that icon is determined, upon closer examination, to in fact be inappropriate (e.g. because it uses an unsupported format), then the user agent must try the next-most-appropriate icon as determined by the attributes.

There is no default type for resources given by the icon keyword. However, for the purposes of determining the type of the resource, user agents must expect the resource to be an image.

The sizes attribute gives the sizes of icons for visual media.

If specified, the attribute must have a value that is an unordered set of unique space-separated tokens. The values must all be either any or a value that consists of two valid non-negative integers that do not have a leading U+0030 DIGIT ZERO (0) character and that are separated by a single U+0078 LATIN SMALL LETTER X character.

The keywords represent icon sizes.

To parse and process the attribute's value, the user agent must first split the attribute's value on spaces, and must then parse each resulting keyword to determine what it represents.

The any keyword represents that the resource contains a scalable icon, e.g. as provided by an SVG image.

Other keywords must be further parsed as follows to determine what they represent:

The keywords specified on the sizes attribute must not represent icon sizes that are not actually available in the linked resource.

If the attribute is not specified, then the user agent must assume that the given icon is appropriate, but less appropriate than an icon of a known and appropriate size.

The following snippet shows the top part of an application with several icons.

<!DOCTYPE HTML>
<html>
 <head>
  <title>lsForums — Inbox</title>
  <link rel=icon href=favicon.png sizes="16x16">
  <link rel=icon href=windows.ico sizes="32x32 48x48">
  <link rel=icon href=mac.icns sizes="128x128 512x512 8192x8192 32768x32768">
  <link rel=icon href=iphone.png sizes="59x60">
  <link rel=icon href=gnome.svg sizes="any">
  <link rel=stylesheet href=lsforums.css>
  <script src=lsforums.js></script>
  <meta name=application-name content="lsForums">
 </head>
 <body>
  ...

The license keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The license keyword indicates that the referenced document provides the copyright license terms under which the current document is provided.

Synonyms: For historical reasons, user agents must also treat the keyword "copyright" like the license keyword.

The nofollow keyword may be used with a and area elements.

The nofollow keyword indicates that the link is not endorsed by the original author or publisher of the page, or that the link to the referenced document was included primarily because of a commercial relationship between people affiliated with the two pages.

The noreferrer keyword may be used with a and area elements.

It indicates that the no referrer information is to be leaked when following the link.

If a user agent follows a link defined by an a or area element that has the noreferrer keyword, the user agent must not include a Referer (sic) HTTP header (or equivalent for other protocols) in the request.

This keyword also causes the opener attribute to remain null if the hyperlink creates a new browsing context.

The pingback keyword may be used with link elements, for which it creates an external resource link.

For the semantics of the pingback keyword, see the Pingback 1.0 specification. [PINGBACK]

The prefetch keyword may be used with link elements, for which it creates an external resource link.

The prefetch keyword indicates that preemptively fetching and caching the specified resource is likely to be beneficial, as it is highly likely that the user will require this resource.

There is no default type for resources given by the prefetch keyword.

The search keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The search keyword indicates that the referenced document provides an interface specifically for searching the document and its related resources.

OpenSearch description documents can be used with link elements and the search link type to enable user agents to autodiscover search interfaces. [OPENSEARCH]

The stylesheet keyword may be used with link elements, for which it creates an external resource link that contributes to the styling processing model.

The specified resource is a resource that describes how to present the document. Exactly how the resource is to be processed depends on the actual type of the resource.

If the alternate keyword is also specified on the link element, then the link is an alternative stylesheet; in this case, the title attribute must be specified on the link element, with a non-empty value.

The default type for resources given by the stylesheet keyword is text/css.

Quirk: If the document has been set to quirks mode and the Content-Type metadata of the external resource is not a supported style sheet type, the user agent must instead assume it to be text/css.

The sidebar keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The sidebar keyword indicates that the referenced document, if retrieved, is intended to be shown in a secondary browsing context (if possible), instead of in the current browsing context.

A hyperlink element with the sidebar keyword specified is a sidebar hyperlink.

The tag keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The tag keyword indicates that the tag that the referenced document represents applies to the current document.

Since it indicates that the tag applies to the current document, it would be inappropriate to use this keyword in the markup of a tag cloud, which lists the popular tag across a set of pages.

Some documents form part of a hierarchical structure of documents.

A hierarchical structure of documents is one where each document can have various subdocuments. The document of which a document is a subdocument is said to be the document's parent. A document with no parent forms the top of the hierarchy.

A document may be part of multiple hierarchies.

The index keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The index keyword indicates that the document is part of a hierarchical structure, and that the link is leading to the document that is the top of the hierarchy. It conveys more information when used with the up keyword (q.v.).

Synonyms: For historical reasons, user agents must also treat the keywords "top", "contents", and "toc" like the index keyword.

The up keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The up keyword indicates that the document is part of a hierarchical structure, and that the link is leading to the document that is the parent of the current document.

The up keyword may be repeated within a rel attribute to indicate the hierarchical distance from the current document to the referenced document. Each occurrence of the keyword represents one further level. If the index keyword is also present, then the number of up keywords is the depth of the current page relative to the top of the hierarchy. Only one link is created for the set of one or more up keywords and, if present, the index keyword.

If the page is part of multiple hierarchies, then they should be described in different paragraphs. User agents must scope any interpretation of the up and index keywords together indicating the depth of the hierarchy to the paragraph in which the link finds itself, if any, or to the document otherwise.

When two links have both the up and index keywords specified together in the same scope and contradict each other by having a different number of up keywords, the link with the greater number of up keywords must be taken as giving the depth of the document.

This can be used to mark up a navigation style sometimes known as bread crumbs. In the following example, the current page can be reached via two paths.

<nav>
 <p>
  <a href="/" rel="index up up up">Main</a> >
  <a href="/products/" rel="up up">Products</a> >
  <a href="/products/dishwashers/" rel="up">Dishwashers</a> >
  <a>Second hand</a>
 </p>
 <p>
  <a href="/" rel="index up up">Main</a> >
  <a href="/second-hand/" rel="up">Second hand</a> >
  <a>Dishwashers</a>
 </p>
</nav>

The relList DOM attribute (e.g. on the a element) does not currently represent multiple up keywords (the interface hides duplicates).

Some documents form part of a sequence of documents.

A sequence of documents is one where each document can have a previous sibling and a next sibling. A document with no previous sibling is the start of its sequence, a document with no next sibling is the end of its sequence.

A document may be part of multiple sequences.

The first keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The first keyword indicates that the document is part of a sequence, and that the link is leading to the document that is the first logical document in the sequence.

Synonyms: For historical reasons, user agents must also treat the keywords "begin" and "start" like the first keyword.

The last keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The last keyword indicates that the document is part of a sequence, and that the link is leading to the document that is the last logical document in the sequence.

Synonyms: For historical reasons, user agents must also treat the keyword "end" like the last keyword.

The next keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The next keyword indicates that the document is part of a sequence, and that the link is leading to the document that is the next logical document in the sequence.

The prev keyword may be used with link, a, and area elements. For link elements, it creates a hyperlink.

The prev keyword indicates that the document is part of a sequence, and that the link is leading to the document that is the previous logical document in the sequence.

Synonyms: For historical reasons, user agents must also treat the keyword "previous" like the prev keyword.

Other than the types defined above, only types defined as extensions in the WHATWG Wiki RelExtensions page may be used with the rel attribute on link, a, and area elements. [WHATWGWIKI]

Anyone is free to edit the WHATWG Wiki RelExtensions page at any time to add a type. Extension types must be specified with the following information:

Keyword

The actual value being defined. The value should not be confusingly similar to any other defined value (e.g. differing only in case).

Effect on... link

One of the following:

not allowed
The keyword is not allowed to be specified on link elements.
Hyperlink
The keyword may be specified on a link element; it creates a hyperlink link.
External Resource
The keyword may be specified on a link element; it creates a external resource link.
Effect on... a and area

One of the following:

not allowed
The keyword is not allowed to be specified on a and area elements.
Hyperlink
The keyword may be specified on a and area elements.
Brief description

A short description of what the keyword's meaning is.

Link to more details

A link to a more detailed description of the keyword's semantics and requirements. It could be another page on the Wiki, or a link to an external page.

Synonyms

A list of other keyword values that have exactly the same processing requirements. Authors must not use the values defined to be synonyms, they are only intended to allow user agents to support legacy content.

Status

One of the following:

Proposal
The keyword has not received wide peer review and approval. It is included for completeness because pages use the keyword. Pages should not use the keyword.
Accepted
The keyword has received wide peer review and approval. It has a specification that unambiguously defines how to handle pages that use the keyword, including when they use them in incorrect ways. Pages may use the keyword.
Rejected
The keyword has received wide peer review and it has been found to have significant problems. Pages must not use the keyword. When a keyword has this status, the "Effect on... link" and "Effect on... a and area" information should be set to "not allowed".

If a keyword is added with the "proposal" status and found to be redundant with existing values, it should be removed and listed as a synonym for the existing value. If a keyword is added with the "proposal" status and found to be harmful, then it should be changed to "rejected" status, and its "Effect on..." information should be changed accordingly.

Conformance checkers must use the information given on the WHATWG Wiki RelExtensions page to establish if a value not explicitly defined in this specification is allowed or not. When an author uses a new type not defined by either this specification or the Wiki page, conformance checkers should offer to add the value to the Wiki, with the details described above, with the "proposal" status.

This specification does not define how new values will get approved. It is expected that the Wiki will have a community that addresses this.

6 User Interaction

This section describes various features that allow authors to enable users to edit documents and parts of documents interactively.

6.1 Introduction

This section is non-normative.

Would be nice to explain how these features work together.

6.2 The hidden attribute

All elements may have the hidden content attribute set. The hidden attribute is a boolean attribute. When specified on an element, it indicates that the element is not yet, or is no longer, relevant. User agents should not render elements that have the hidden attribute specified.

In the following skeletal example, the attribute is used to hide the Web game's main screen until the user logs in:

  <h1>The Example Game</h1>
  <section id="login">
   <h2>Login</h2>
   <form>
    ...
    <!-- calls login() once the user's credentials have been checked -->
   </form>
   <script>
    function login() {
      // switch screens
      document.getElementById('login').hidden = true;
      document.getElementById('game').hidden = false;
    }
   </script>
  </section>
  <section id="game" hidden>
   ...
  </section>

The hidden attribute must not be used to hide content that could legitimately be shown in another presentation. For example, it is incorrect to use hidden to hide panels in a tabbed dialog, because the tabbed interface is merely a kind of overflow presentation — showing all the form controls in one big page with a scrollbar would be equivalent, and no less correct.

Elements in a section hidden by the hidden attribute are still active, e.g. scripts and form controls in such sections still render execute and submit respectively. Only their presentation to the user changes.

The hidden DOM attribute must reflect the content attribute of the same name.

6.3 Activation

element . click()

Acts as if the element was clicked.

Each element has a click in progress flag, initially set to false.

The click() method must run these steps:

  1. If the element's click in progress flag is set to true, then abort these steps.

  2. Set the click in progress flag on the element to true.

  3. If the element has a defined activation behavior, run synthetic click activation steps on the element. Otherwise, fire a click event at the element.

  4. Set the click in progress flag on the element to false.

6.4 Scrolling elements into view

element . scrollIntoView( [ top ] )

Scrolls the element into view. If the top argument is true, then the element will be scrolled to the top of the viewport, otherwise it'll be scrolled to the bottom. The default is the top.

The scrollIntoView([top]) method, when called, must cause the element on which the method was called to have the attention of the user called to it.

In a speech browser, this could happen by having the current playback position move to the start of the given element.

In visual user agents, if the argument is present and has the value false, the user agent should scroll the element into view such that both the bottom and the top of the element are in the viewport, with the bottom of the element aligned with the bottom of the viewport. If it isn't possible to show the entire element in that way, or if the argument is omitted or is true, then the user agent should instead align the top of the element with the top of the viewport. If the entire scrollable part of the content is visible all at once (e.g. if a page is shorter than the viewport), then the user agent should not scroll anything. Visual user agents should further scroll horizontally as necessary to bring the element to the attention of the user.

Non-visual user agents may ignore the argument, or may treat it in some media-specific manner most useful to the user.

6.5 Focus

When an element is focused, key events received by the document must be targeted at that element. There may be no element focused; when no element is focused, key events received by the document must be targeted at the body element.

User agents may track focus for each browsing context or Document individually, or may support only one focused element per top-level browsing context — user agents should follow platform conventions in this regard.

Which elements within a top-level browsing context currently have focus must be independent of whether or not the top-level browsing context itself has the system focus.

When an element is focused, the element matches the CSS :focus pseudo-class.

6.5.1 Sequential focus navigation

The tabindex content attribute specifies whether the element is focusable, whether it can be reached using sequential focus navigation, and the relative order of the element for the purposes of sequential focus navigation. The name "tab index" comes from the common use of the "tab" key to navigate through the focusable elements. The term "tabbing" refers to moving forward through the focusable elements that can be reached using sequential focus navigation.

The tabindex attribute, if specified, must have a value that is a valid integer.

If the attribute is specified, it must be parsed using the rules for parsing integers. The attribute's values have the following meanings:

If the attribute is omitted or parsing the value returns an error

The user agent should follow platform conventions to determine if the element is to be focusable and, if so, whether the element can be reached using sequential focus navigation, and if so, what its relative order should be.

If the value is a negative integer

The user agent must allow the element to be focused, but should not allow the element to be reached using sequential focus navigation.

If the value is a zero

The user agent must allow the element to be focused, should allow the element to be reached using sequential focus navigation, and should follow platform conventions to determine the element's relative order.

If the value is greater than zero

The user agent must allow the element to be focused, should allow the element to be reached using sequential focus navigation, and should place the element in the sequential focus navigation order so that it is:

  • before any focusable element whose tabindex attribute has been omitted or whose value, when parsed, returns an error,
  • before any focusable element whose tabindex attribute has a value equal to or less than zero,
  • after any element whose tabindex attribute has a value greater than zero but less than the value of the tabindex attribute on the element,
  • after any element whose tabindex attribute has a value equal to the value of the tabindex attribute on the element but that is earlier in the document in tree order than the element,
  • before any element whose tabindex attribute has a value equal to the value of the tabindex attribute on the element but that is later in the document in tree order than the element, and
  • before any element whose tabindex attribute has a value greater than the value of the tabindex attribute on the element.

An element is specially focusable if the tabindex attribute's definition above defines the element to be focusable.

An element that is specially focusable but does not otherwise have an activation behavior defined has an activation behavior that does nothing.

This means that an element that is only focusable because of its tabindex attribute will fire a click event in response to a non-mouse activation (e.g. hitting the "enter" key while the element is focused).

An element is focusable if the user agent's default behavior allows it to be focusable or if the element is specially focusable, but only if the element is being rendered.

User agents should make the following elements focusable, unless platform conventions dictate otherwise:

The tabIndex DOM attribute must reflect the value of the tabindex content attribute. If the attribute is not present, or parsing its value returns an error, then the DOM attribute must return 0 for elements that are focusable and −1 for elements that are not focusable.

6.5.2 Focus management

The focusing steps are as follows:

  1. If focusing the element will remove the focus from another element, then run the unfocusing steps for that element.

  2. Make the element the currently focused element in its top-level browsing context.

    Some elements, most notably area, can correspond to more than one distinct focusable area. If a particular area was indicated when the element was focused, then that is the area that must get focus; otherwise, e.g. when using the focus() method, the first such region in tree order is the one that must be focused.

  3. Fire a simple event called focus at the element.

User agents must run the focusing steps for an element whenever the user moves the focus to a focusable element.

The unfocusing steps are as follows:

  1. If the element is an input element, and the change event applies to the element, and the element does not have a defined activation behavior, and the user has changed the element's value or its list of selected files while the control was focused without committing that change, then fire a simple event called change at the element, then broadcast formchange events at the element's form owner.

  2. Unfocus the element.

  3. Fire a simple event that doesn't bubble called blur at the element.

When an element that is focused stops being a focusable element, or stops being focused without another element being explicitly focused in its stead, the user agent should run the focusing steps for the body element, if there is one; if there is not, then the user agent should run the unfocusing steps for the affected element only.

For example, this might happen because the element is removed from its Document, or has a hidden attribute added. It would also happen to an input element when the element gets disabled.

6.5.3 Document-level focus APIs

document . activeElement

Returns the currently focused element.

document . hasFocus()

Returns true if the document has focus; otherwise, returns false.

window . focus()

Focuses the window. Use of this method is discouraged. Allow the user to control window focus instead.

window . blur()

Unfocuses the window. Use of this method is discouraged. Allow the user to control window focus instead.

The activeElement attribute on DocumentHTML objects must return the element in the document that is focused. If no element in the Document is focused, this must return the body element.

The hasFocus() method on DocumentHTML objects must return true if the document's browsing context is focused, and all its ancestor browsing contexts are also focused, and the top-level browsing context has the system focus.

The focus() method on the Window object, when invoked, provides a hint to the user agent that the script believes the user might be interested in the contents of the browsing context of the Window object on which the method was invoked.

User agents are encouraged to have this focus() method trigger some kind of notification.

The blur() method on the Window object, when invoked, provides a hint to the user agent that the script believes the user probably is not currently interested in the contents of the browsing context of the Window object on which the method was invoked, but that the contents might become interesting again in the future.

User agents are encouraged to ignore calls to this blur() method entirely.

Historically the focus() and blur() methods actually affected the system focus, but hostile sites widely abuse this behavior to the user's detriment.

6.5.4 Element-level focus APIs

element . focus()

Focuses the element.

element . blur()

Unfocuses the element. Use of this method is discouraged. Focus another element instead.

The focus() method, when invoked, must run the following algorithm:

  1. If the element is marked as locked for focus, then abort these steps.

  2. If the element is not focusable, then abort these steps.

  3. Mark the element as locked for focus.

  4. If the element is not already focused, run the focusing steps for the element.

  5. Unmark the element as locked for focus.

The blur() method, when invoked, should run the focusing steps for the body element, if there is one; if there is not, then it should run the unfocusing steps for the element on which the method was called instead. User agents may selectively or uniformly ignore calls to this method for usability reasons.

6.6 The text selection APIs

Every browsing context has a selection. The selection can be empty, and the selection can have more than one range (a disjointed selection). The user agent should allow the user to change the selection. User agents are not required to let the user select more than one range, and may collapse multiple ranges in the selection to a single range when the user interacts with the selection. (But, of course, the user agent may let the user create selections with multiple ranges.)

This one selection must be shared by all the content of the browsing context (though not by nested browsing contexts), including any editing hosts in the document. (Editing hosts that are not inside a document cannot have a selection.)

If the selection is empty (collapsed, so that it has only one segment and that segment's start and end points are the same) then the selection's position should equal the caret position. When the selection is not empty, this specification does not define the caret position; user agents should follow platform conventions in deciding whether the caret is at the start of the selection, the end of the selection, or somewhere else.

On some platforms (such as those using Wordstar editing conventions), the caret position is totally independent of the start and end of the selection, even when the selection is empty. On such platforms, user agents may ignore the requirement that the cursor position be linked to the position of the selection altogether.

Mostly for historical reasons, in addition to the browsing context's selection, each textarea and input element has an independent selection. These are the text field selections.

User agents may selectively ignore attempts to use the API to adjust the selection made after the user has modified the selection. For example, if the user has just selected part of a word, the user agent could ignore attempts to use the API call to immediately unselect the selection altogether, but could allow attempts to change the selection to select the entire word.

User agents may also allow the user to create selections that are not exposed to the API.

The select element also has a selection, indicating which items have been picked by the user. This is not discussed in this section.

This specification does not specify how selections are presented to the user. The Selectors specification, in conjunction with CSS, can be used to style text selections using the ::selection pseudo-element. [SELECTORS] [CSS21]

6.6.1 APIs for the browsing context selection

window . getSelection()
document . getSelection()

Returns the Selection object for the window, which stringifies to the text of the current selection.

The getSelection() method on the Window interface must return the Selection object representing the selection of that Window object's browsing context.

For historical reasons, the getSelection() method on the HTMLDocument interface must return the same Selection object.

[Stringifies] interface Selection {
  readonly attribute Node anchorNode;
  readonly attribute long anchorOffset;
  readonly attribute Node focusNode;
  readonly attribute long focusOffset;
  readonly attribute boolean isCollapsed;
  void collapse(in Node parentNode, in long offset);
  void collapseToStart();
  void collapseToEnd();
  void selectAllChildren(in Node parentNode);
  void deleteFromDocument();
  readonly attribute long rangeCount;
  Range getRangeAt(in long index);
  void addRange(in Range range);
  void removeRange(in Range range);
  void removeAllRanges();
};

The Selection interface is represents a list of Range objects. The first item in the list has index 0, and the last item has index count-1, where count is the number of ranges in the list. [DOM2RANGE]

All of the members of the Selection interface are defined in terms of operations on the Range objects represented by this object. These operations can raise exceptions, as defined for the Range interface; this can therefore result in the members of the Selection interface raising exceptions as well, in addition to any explicitly called out below.

selection . anchorNode

Returns the element that contains the start of the selection.

Returns null if there's no selection.

selection . anchorOffset

Returns the offset of the start of the selection relative to the element that contains the start of the selection.

Returns 0 if there's no selection.

selection . focusNode

Returns the element that contains the end of the selection.

Returns null if there's no selection.

selection . focusOffset

Returns the offset of the end of the selection relative to the element that contains the end of the selection.

Returns 0 if there's no selection.

collapsed = selection . isCollapsed()

Returns true if there's no selection or if the selection is empty. Otherwise, returns false.

selection . collapsed(parentNode, offset)

Replaces the selection with an empty one at the given position.

Throws a WRONG_DOCUMENT_ERR exception if the given node is in a different document.

selection . collapseToStart()

Replaces the selection with an empty one at the position of the start of the current selection.

Throws an INVALID_STATE_ERR exception if there is no selection.

selection . collapseToEnd()

Replaces the selection with an empty one at the position of the end of the current selection.

Throws an INVALID_STATE_ERR exception if there is no selection.

selection . selectAllChildren(parentNode)

Replaces the selection with one that contains all the contents of the given element.

Throws a WRONG_DOCUMENT_ERR exception if the given node is in a different document.

selection . deleteFromDocument()

Deletes the selection.

selection . rangeCount

Returns the number of ranges in the selection.

selection . getRangeAt(index)

Returns the given range.

Throws an INVALID_STATE_ERR exception if the value is out of range.

selection . addRange(range)

Adds the given range to the selection.

selection . removeRange(range)

Removes the given range from the selection, if the range was one of the ones in the selection.

selection . removeAllRanges()

Removes all the ranges in the selection.

The anchorNode attribute must return the value returned by the startContainer attribute of the last Range object in the list, or null if the list is empty.

The anchorOffset attribute must return the value returned by the startOffset attribute of the last Range object in the list, or 0 if the list is empty.

The focusNode attribute must return the value returned by the endContainer attribute of the last Range object in the list, or null if the list is empty.

The focusOffset attribute must return the value returned by the endOffset attribute of the last Range object in the list, or 0 if the list is empty.

The isCollapsed attribute must return true if there are zero ranges, or if there is exactly one range and its collapsed attribute is itself true. Otherwise it must return false.

The collapse(parentNode, offset) method must raise a WRONG_DOCUMENT_ERR DOM exception if parentNode's Document is not the HTMLDocument object with which the Selection object is associated. Otherwise it is, and the method must remove all the ranges in the Selection list, then create a new Range object, add it to the list, and invoke its setStart() and setEnd() methods with the parentNode and offset values as their arguments.

The collapseToStart() method must raise an INVALID_STATE_ERR DOM exception if there are no ranges in the list. Otherwise, it must invoke the collapse() method with the startContainer and startOffset values of the first Range object in the list as the arguments.

The collapseToEnd() method must raise an INVALID_STATE_ERR DOM exception if there are no ranges in the list. Otherwise, it must invoke the collapse() method with the endContainer and endOffset values of the last Range object in the list as the arguments.

The selectAllChildren(parentNode) method must invoke the collapse() method with the parentNode value as the first argument and 0 as the second argument, and must then invoke the selectNodeContents() method on the first (and only) range in the list with the parentNode value as the argument.

The deleteFromDocument() method must invoke the deleteContents() method on each range in the list, if any, from first to last.

The rangeCount attribute must return the number of ranges in the list.

The getRangeAt(index) method must return the indexth range in the list. If index is less than zero or greater or equal to the value returned by the rangeCount attribute, then the method must raise an INDEX_SIZE_ERR DOM exception.

The addRange(range) method must add the given range Range object to the list of selections, at the end (so the newly added range is the new last range). Duplicates are not prevented; a range may be added more than once in which case it appears in the list more than once, which (for example) will cause stringification to return the range's text twice.

The removeRange(range) method must remove the first occurrence of range in the list of ranges, if it appears at all.

The removeAllRanges() method must remove all the ranges from the list of ranges, such that the rangeCount attribute returns 0 after the removeAllRanges() method is invoked (and until a new range is added to the list, either through this interface or via user interaction).

Objects implementing this interface must stringify to a concatenation of the results of invoking the toString() method of the Range object on each of the ranges of the selection, in the order they appear in the list (first to last).

In the following document fragment, the emphasized parts indicate the selection.

<p>The cute girl likes the <cite>Oxford English Dictionary</cite>.</p>

If a script invoked window.getSelection().toString(), the return value would be "the Oxford English".

6.6.2 APIs for the text field selections

The input and textarea elements define the following members in their DOM interfaces for handling their text selection:

  void select();
           attribute unsigned long selectionStart;
           attribute unsigned long selectionEnd;
  void setSelectionRange(in unsigned long start, in unsigned long end);

These methods and attributes expose and control the selection of input and textarea text fields.

element . select()

Selects everything in the text field.

element . selectionStart [ = value ]

Returns the offset to the start of the selection.

Can be set, to change the start of the selection.

element . selectionEnd [ = value ]

Returns the offset to the end of the selection.

Can be set, to change the end of the selection.

element . setSelectionRange(start, end)

Changes the selection to cover the given substring.

When these methods and attributes are used with input elements while they don't apply, they must raise an INVALID_STATE_ERR exception. Otherwise, they must act as described below.

The select() method must cause the contents of the text field to be fully selected.

The selectionStart attribute must, on getting, return the offset (in logical order) to the character that immediately follows the start of the selection. If there is no selection, then it must return the offset (in logical order) to the character that immediately follows the text entry cursor.

On setting, it must act as if the setSelectionRange() method had been called, with the new value as the first argument, and the current value of the selectionEnd attribute as the second argument, unless the current value of the selectionEnd is less than the new value, in which case the second argument must also be the new value.

The selectionEnd attribute must, on getting, return the offset (in logical order) to the character that immediately follows the end of the selection. If there is no selection, then it must return the offset (in logical order) to the character that immediately follows the text entry cursor.

On setting, it must act as if the setSelectionRange() method had been called, with the current value of the selectionStart attribute as the first argument, and new value as the second argument.

The setSelectionRange(start, end) method must set the selection of the text field to the sequence of characters starting with the character at the startth position (in logical order) and ending with the character at the (end-1)th position. Arguments greater than the length of the value in the text field must be treated as pointing at the end of the text field. If end is less than or equal to start then the start of the selection and the end of the selection must both be placed immediately before the character with offset end. In UAs where there is no concept of an empty selection, this must set the cursor to be just before the character with offset end.

To obtain the currently selected text, the following JavaScript suffices:

var selectionText = control.value.substring(control.selectionStart, control.selectionEnd);

...where control is the input or textarea element.

Characters with no visible rendering, such as U+200D ZERO WIDTH JOINER, still count as characters. Thus, for instance, the selection can include just an invisible character, and the text insertion cursor can be placed to one side or another of such a character.

6.7 The contenteditable attribute

The contenteditable attribute is an enumerated attribute whose keywords are the empty string, true, and false. The empty string and the true keyword map to the true state. The false keyword maps to the false state. In addition, there is a third state, the inherit state, which is the missing value default (and the invalid value default).

The true state indicates that the element is editable. The inherit state indicates that the element is editable if its parent is. The false state indicates that the element is not editable.

Specifically, if an HTML element has a contenteditable attribute set to the true state, or it has its contenteditable attribute set to the inherit state and if its nearest ancestor HTML element with the contenteditable attribute set to a state other than the inherit state has its attribute set to the true state, or if it and its ancestors all have their contenteditable attribute set to the inherit state but the Document has designMode enabled, then the UA must treat the element as editable (as described below).

Otherwise, either the HTML element has a contenteditable attribute set to the false state, or its contenteditable attribute is set to the inherit state and its nearest ancestor HTML element with the contenteditable attribute set to a state other than the inherit state has its attribute set to the false state, or all its ancestors have their contenteditable attribute set to the inherit state and the Document itself has designMode disabled; either way, the element is not editable.

element . contentEditable [ = value ]

Returns "true", "false", or "inherit", based on the state of the contenteditable attribute.

Can be set, to change that state.

Throws a SYNTAX_ERR exception if the new value isn't one of those strings.

element . isContentEditable

Returns true if the element is editable; otherwise, returns false.

The contentEditable DOM attribute, on getting, must return the string "true" if the content attribute is set to the true state, false" if the content attribute is set to the false state, and "inherit" otherwise. On setting, if the new value is an ASCII case-insensitive match for the string "inherit" then the content attribute must be removed, if the new value is an ASCII case-insensitive match for the string "true" then the content attribute must be set to the string "true", if the new value is an ASCII case-insensitive match for the string "false" then the content attribute must be set to the string "false", and otherwise the attribute setter must raise a SYNTAX_ERR exception.

The isContentEditable DOM attribute, on getting, must return true if the element is editable, and false otherwise.

If an element is editable and its parent element is not, or if an element is editable and it has no parent element, then the element is an editing host. Editable elements can be nested. User agents must make editing hosts focusable (which typically means they enter the tab order). An editing host can contain non-editable sections, these are handled as described below. An editing host can contain non-editable sections that contain further editing hosts.

When an editing host has focus, it must have a caret position that specifies where the current editing position is. It may also have a selection.

How the caret and selection are represented depends entirely on the UA.

6.7.1 User editing actions

There are several actions that the user agent should allow the user to perform while the user is interacting with an editing host. How exactly each action is triggered is not defined for every action, but when it is not defined, suggested key bindings are provided to guide implementors.

Move the caret

User agents must allow users to move the caret to any position within an editing host, even into nested editable elements. This could be triggered as the default action of keydown events with various key identifiers and as the default action of mousedown events.

Change the selection

User agents must allow users to change the selection within an editing host, even into nested editable elements. User agents may prevent selections from being made in ways that cross from editable elements into non-editable elements (e.g. by making each non-editable descendant atomically selectable, but not allowing text selection within them). This could be triggered as the default action of keydown events with various key identifiers and as the default action of mousedown events.

Insert text

This action must be triggered as the default action of a textInput event, and may be triggered by other commands as well. It must cause the user agent to insert the specified text (given by the event object's data attribute in the case of the textInput event) at the caret.

If the caret is positioned somewhere where phrasing content is not allowed (e.g. inside an empty ol element), then the user agent must not insert the text directly at the caret position. In such cases the behavior is UA-dependent, but user agents must not, in response to a request to insert text, generate a DOM that is less conformant than the DOM prior to the request.

User agents should allow users to insert new paragraphs into elements that contains only content other than paragraphs.

For example, given the markup:

<section>
 <dl>
  <dt> Ben </dt>
  <dd> Goat </dd>
 </dl>
</section>

...the user agent should allow the user to insert p elements before and after the dl element, as children of the section element.

Break block

UAs should offer a way for the user to request that the current paragraph be broken at the caret, e.g. as the default action of a keydown event whose identifier is the "Enter" key and that has no modifiers set.

The exact behavior is UA-dependent, but user agents must not, in response to a request to break a paragraph, generate a DOM that is less conformant than the DOM prior to the request.

Insert a line separator

UAs should offer a way for the user to request an explicit line break at the caret position without breaking the paragraph, e.g. as the default action of a keydown event whose identifier is the "Enter" key and that has a shift modifier set. Line separators are typically found within a poem verse or an address. To insert a line break, the user agent must insert a br element.

If the caret is positioned somewhere where phrasing content is not allowed (e.g. in an empty ol element), then the user agent must not insert the br element directly at the caret position. In such cases the behavior is UA-dependent, but user agents must not, in response to a request to insert a line separator, generate a DOM that is less conformant than the DOM prior to the request.

Delete

UAs should offer a way for the user to delete text and elements, including non-editable descendants, e.g. as the default action of keydown events whose identifiers are "U+0008" or "U+007F".

Five edge cases in particular need to be considered carefully when implementing this feature: backspacing at the start of an element, backspacing when the caret is immediately after an element, forward-deleting at the end of an element, forward-deleting when the caret is immediately before an element, and deleting a selection whose start and end points do not share a common parent node.

In any case, the exact behavior is UA-dependent, but user agents must not, in response to a request to delete text or an element, generate a DOM that is less conformant than the DOM prior to the request.

Insert, and wrap text in, semantic elements

UAs should offer the user the ability to mark text and paragraphs with semantics that HTML can express.

UAs should similarly offer a way for the user to insert empty semantic elements to subsequently fill by entering text manually.

UAs should also offer a way to remove those semantics from marked up text, and to remove empty semantic element that have been inserted.

In response to a request from a user to mark text up in italics, user agents should use the i element to represent the semantic. The em element should be used only if the user agent is sure that the user means to indicate stress emphasis.

In response to a request from a user to mark text up in bold, user agents should use the b element to represent the semantic. The strong element should be used only if the user agent is sure that the user means to indicate importance.

The exact behavior is UA-dependent, but user agents must not, in response to a request to wrap semantics around some text or to insert or remove a semantic element, generate a DOM that is less conformant than the DOM prior to the request.

Select and move non-editable elements nested inside editing hosts

UAs should offer a way for the user to move images and other non-editable parts around the content within an editing host. This may be done using the drag and drop mechanism. User agents must not, in response to a request to move non-editable elements nested inside editing hosts, generate a DOM that is less conformant than the DOM prior to the request.

Edit form controls nested inside editing hosts

When an editable form control is edited, the changes must be reflected in both its current value and its default value. For input elements this means updating the defaultValue DOM attribute as well as the value DOM attribute; for select elements it means updating the option elements' defaultSelected DOM attribute as well as the selected DOM attribute; for textarea elements this means updating the defaultValue DOM attribute as well as the value DOM attribute. (Updating the default* DOM attributes causes content attributes to be updated as well.)

User agents may perform several commands per user request; for example if the user selects a block of text and hits Enter, the UA might interpret that as a request to delete the content of the selection followed by a request to break the paragraph at that position.

All of the actions defined above, whether triggered by the user or programmatically (e.g. by execCommand() commands), must fire mutation events as appropriate.

6.7.2 Making entire documents editable

Documents have a designMode, which can be either enabled or disabled.

document . designMode [ = value ]

Returns "on" if the document is editable, and "off" if it isn't.

Can be set, to change the document's current state.

The designMode DOM attribute on the Document object takes two values, "on" and "off". When it is set, the new value must be compared in an ASCII case-insensitive manner to these two values. If it matches the "on" value, then designMode must be enabled, and if it matches the "off" value, then designMode must be disabled. Other values must be ignored.

When designMode is enabled, the DOM attribute must return the value "on", and when it is disabled, it must return the value "off".

The last state set must persist until the document is destroyed or the state is changed. Initially, documents must have their designMode disabled.

6.8 Spelling and grammar checking

User agents can support the checking of spelling and grammar of editable text, either in form controls (such as the value of textarea elements), or in elements in an editing host (using contenteditable).

For each element, user agents must establish a default behavior, either through defaults or through preferences expressed by the user. There are three possible default behaviors for each element:

true-by-default
The element will be checked for spelling and grammar if its contents are editable.
false-by-default
The element will never be checked for spelling and grammar.
inherit-by-default
The element's default behavior is the same as its parent element's. Elements that have no parent element cannot have this as their default behavior.

The spellcheck attribute is an enumerated attribute whose keywords are the empty string, true and false. The empty string and the true keyword map to the true state. The false keyword maps to the false state. In addition, there is a third state, the inherit state, which is the missing value default (and the invalid value default).

The true state indicates that the element is to have its spelling and grammar checked. The inherit state indicates that the element is to act the same way as its parent. The false state indicates that the element is not to be checked.


element . spellcheck [ = value ]

Returns true if the element is to have its spelling and grammar checked; otherwise, returns false.

Can be set, to override the default and set the spellcheck content attribute.

The spellcheck DOM attribute, on getting, must return true if the element's spellcheck content attribute is in the true state, or if the element's spellcheck content attribute is in the inherit state and the element's default behavior is true-by-default, or if the element's spellcheck content attribute is in the inherit state and the element's default behavior is inherit-by-default and the element's parent element's spellcheck DOM attribute would return true; otherwise, if none of those conditions applies, then the attribute must instead return false.

The spellcheck DOM attribute is not affected by user preferences that override the spellcheck content attribute, and therefore might not reflect the actual spellchecking state.

On setting, if the new value is true, then the element's spellcheck content attribute must be set to the literal string "true", otherwise it must be set to the literal string "false".


User agents must only consider the following pieces of text as checkable for the purposes of this feature:

For text that is part of a text node, the element with which the text is associated is the element that is the immediate parent of the first character of the word, sentence, or other piece of text. For text in attributes, it is the attribute's element. For the values of input and textarea elements, it is the element itself.

To determine if a word, sentence, or other piece of text in an applicable element (as defined above) is to have spelling- and/or grammar-checking enabled, the UA must use the following algorithm:

  1. If the user has disabled the checking for this text, then the checking is disabled.
  2. Otherwise, if the user has forced the checking for this text to always be enabled, then the checking is enabled.
  3. Otherwise, if the element with which the text is associated has a spellcheck content attribute, then: if that attribute is in the true state, then checking is enabled; otherwise, if that attribute is in the false state, then checking is disabled.
  4. Otherwise, if there is an ancestor element with a spellcheck content attribute that is not in the inherit state, then: if the nearest such ancestor's spellcheck content attribute is in the true state, then checking is enabled; otherwise, checking is disabled.
  5. Otherwise, if the element's default behavior is true-by-default, then checking is enabled.
  6. Otherwise, if the element's default behavior is false-by-default, then checking is disabled.
  7. Otherwise, if the element's parent element has its checking enabled, then checking is enabled.
  8. Otherwise, checking is disabled.

If the checking is enabled for a word/sentence/text, the user agent should indicate spelling and/or grammar errors in that text. User agents should take into account the other semantics given in the document when suggesting spelling and grammar corrections. User agents may use the language of the element to determine what spelling and grammar rules to use, or may use the user's preferred language settings. UAs should use input element attributes such as pattern to ensure that the resulting value is valid, where possible.

If checking is disabled, the user agent should not indicate spelling or grammar errors for that text.

The element with ID "a" in the following example would be the one used to determine if the word "Hello" is checked for spelling errors. In this example, it would not be.

<div contenteditable="true">
 <span spellcheck="false" id="a">Hell</span><em>o!</em>
</div>

The element with ID "b" in the following example would have checking enabled (the leading space character in the attribute's value on the input element causes the attribute to be ignored, so the ancestor's value is used instead, regardless of the default).

<p spellcheck="true">
 <label>Name: <input spellcheck=" false" id="b"></label>
</p>

6.9 Drag and drop

This section defines an event-based drag-and-drop mechanism.

This specification does not define exactly what a drag-and-drop operation actually is.

On a visual medium with a pointing device, a drag operation could be the default action of a mousedown event that is followed by a series of mousemove events, and the drop could be triggered by the mouse being released.

On media without a pointing device, the user would probably have to explicitly indicate his intention to perform a drag-and-drop operation, stating what he wishes to drag and what he wishes to drop, respectively.

However it is implemented, drag-and-drop operations must have a starting point (e.g. where the mouse was clicked, or the start of the selection or element that was selected for the drag), may have any number of intermediate steps (elements that the mouse moves over during a drag, or elements that the user picks as possible drop points as he cycles through possibilities), and must either have an end point (the element above which the mouse button was released, or the element that was finally selected), or be canceled. The end point must be the last element selected as a possible drop point before the drop occurs (so if the operation is not canceled, there must be at least one element in the middle step).

6.9.1 Introduction

This section is non-normative.

It's also currently non-existent.

6.9.2 The DragEvent and DataTransfer interfaces

The drag-and-drop processing model involves several events. They all use the DragEvent interface.

interface DragEvent : MouseEvent {
  readonly attribute DataTransfer dataTransfer;

  void initDragEvent(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in AbstractView viewArg, in long detailArg, in long screenXArg, in long screenYArg, in long clientXArg, in long clientYArg, in boolean ctrlKeyArg, in boolean altKeyArg, in boolean shiftKeyArg, in boolean metaKeyArg, in unsigned short buttonArg, in EventTarget relatedTargetArg, in DataTransfer dataTransferArg);
  void initDragEventNS(in DOMString namespaceURIArg, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in AbstractView viewArg, in long detailArg, in long screenXArg, in long screenYArg, in long clientXArg, in long clientYArg, in unsigned short buttonArg, in EventTarget relatedTargetArg, in DOMString modifiersListArg, in DataTransfer dataTransferArg);
};
event . dataTransfer

Returns the DataTransfer object for the event.

The initDragEvent() and initDragEventNS() methods must initialize the event in a manner analogous to the similarly-named methods in the DOM3 Events interfaces. [DOM3EVENTS]

The initDragEvent() and initDragEventNS() methods handle modifier keys differently, much like the equivalent methods on the MouseEvent interface.

The dataTransfer attribute of the DragEvent interface represents the context information for the event.

interface DataTransfer {
           attribute DOMString dropEffect;
           attribute DOMString effectAllowed;
  readonly attribute DOMStringList types;
  void clearData([Optional] in DOMString format);
  void setData(in DOMString format, in DOMString data);
  DOMString getData(in DOMString format);
  void setDragImage(in Element image, in long x, in long y);
  void addElement(in Element element);
};

DataTransfer objects can hold pieces of data, each associated with a unique format. Formats are generally given by MIME types, with some values special-cased for legacy reasons. For the purposes of this API, however, the format strings are opaque, case-sensitive, strings, and the empty string is a valid format string.

dataTransfer . dropEffect [ = value ]

Returns the kind of operation that is currently selected. If the kind of operation isn't one of those that is allowed by the effectAllowed attribute, then the operation will fail.

Can be set, to change the selected operation.

The possible values are none, copy, link, and move.

dataTransfer . effectAllowed [ = value ]

Returns the kinds of operations that are to be allowed.

Can be set, to change the allowed operations.

The possible values are none, copy, copyLink, copyMove, link, linkMove, move, all, and uninitialized,

dataTransfer . types

Returns a DOMStringList of the formats available.

dataTransfer . clearData( [ format ] )

Removes the data of the specified formats. Removes all data if the argument is omitted.

dataTransfer . setData(format, data)

Adds the specified data.

data = dataTransfer . getData(format)

Returns the specified data. If there is no such data, returns the empty string.

dataTransfer . setDragImage(element, x, y)

Uses the given element to update the drag feedback, replacing any previously specified feedback.

dataTransfer . addElement(element)

Adds the given element to the list of elements used to render the drag feedback.

When a DataTransfer object is created, it must be initialized as follows:

The dropEffect attribute controls the drag-and-drop feedback that the user is given during a drag-and-drop operation.

The attribute must ignore any attempts to set it to a value other than none, copy, link, and move. On getting, the attribute must return the last of those four values that it was set to.

The effectAllowed attribute is used in the drag-and-drop processing model to initialize the dropEffect attribute during the dragenter and dragover events.

The attribute must ignore any attempts to set it to a value other than none, copy, copyLink, copyMove, link, linkMove, move, all, and uninitialized. On getting, the attribute must return the last of those values that it was set to.

The types attribute must return a live DOMStringList that contains the list of formats that are stored in the DataTransfer object.

The clearData() method, when called with no arguments, must clear the DataTransfer object of all data (for all formats).

When called with an argument, the clearData(format) method must clear the DataTransfer object of any data associated with the given format. If format is the value "Text", then it must be treated as "text/plain". If the format is "URL", then it must be treated as "text/uri-list".

The setData(format, data) method must add data to the data stored in the DataTransfer object, labeled as being of the type format. This must replace any previous data that had been set for that format. If format is the value "Text", then it must be treated as "text/plain". If the format is "URL", then it must be treated as "text/uri-list".

The getData(format) method must return the data that is associated with the type format, if any, and must return the empty string otherwise. If format is the value "Text", then it must be treated as "text/plain". If the format is "URL", then the data associated with the "text/uri-list" format must be parsed as appropriate for text/uri-list data, and the first URL from the list must be returned. If there is no data with that format, or if there is but it has no URLs, then the method must return the empty string. [RFC2483]

The setDragImage(element, x, y) method sets which element to use to generate the drag feedback. The element argument can be any Element; if it is an img element, then the user agent should use the element's image (at its intrinsic size) to generate the feedback, otherwise the user agent should base the feedback on the given element (but the exact mechanism for doing so is not specified).

The addElement(element) method is an alternative way of specifying how the user agent is to render the drag feedback. It adds an element to the DataTransfer object.

The difference between setDragImage() and addElement() is that the latter automatically generates the image based on the current rendering of the elements added, whereas the former uses the exact specified image.

6.9.3 Events fired during a drag-and-drop action

The following events are involved in the drag-and-drop model. Whenever the processing model described below causes one of these events to be fired, the event fired must use the DragEvent interface defined above, must have the bubbling and cancelable behaviors given in the table below, and must have the context information set up as described after the table, with the view attribute set to the view with which the user interacted to trigger the drag-and-drop event, the detail attribute set to zero, the mouse and key attributes set according to the state of the input devices as they would be for user interaction events, and the relatedTarget attribute set to null.

Event Name Target Bubbles? Cancelable? dataTransfer effectAllowed dropEffect Default Action
dragstart Source node ✓ Bubbles ✓ Cancelable Contains source node unless a selection is being dragged, in which case it is empty uninitialized none Initiate the drag-and-drop operation
drag Source node ✓ Bubbles ✓ Cancelable Empty Same as last event none Continue the drag-and-drop operation
dragenter Immediate user selection or the body element ✓ Bubbles ✓ Cancelable Empty Same as last event Based on effectAllowed value Reject immediate user selection as potential target element
dragleave Previous target element ✓ Bubbles Empty Same as last event none None
dragover Current target element ✓ Bubbles ✓ Cancelable Empty Same as last event Based on effectAllowed value Reset the current drag operation to "none"
drop Current target element ✓ Bubbles ✓ Cancelable getData() returns data set in dragstart event Same as last event Current drag operation Varies
dragend Source node ✓ Bubbles Empty Same as last event Current drag operation Varies

The dataTransfer object's contents are empty except for dragstart events and drop events, for which the contents are set as described in the processing model, below.

The effectAllowed attribute must be set to "uninitialized" for dragstart events, and to whatever value the field had after the last drag-and-drop event was fired for all other events (only counting events fired by the user agent for the purposes of the drag-and-drop model described below).

The dropEffect attribute must be set to "none" for dragstart, drag, and dragleave events (except when stated otherwise in the algorithms given in the sections below), to the value corresponding to the current drag operation for drop and dragend events, and to a value based on the effectAllowed attribute's value and to the drag-and-drop source, as given by the following table, for the remaining events (dragenter and dragover):

effectAllowed dropEffect
none none
copy, copyLink, copyMove, all copy
link, linkMove link
move move
uninitialized when what is being dragged is a selection from a text field move
uninitialized when what is being dragged is a selection copy
uninitialized when what is being dragged is an a element with an href attribute link
Any other case copy

6.9.4 Drag-and-drop processing model

When the user attempts to begin a drag operation, the user agent must first determine what is being dragged. If the drag operation was invoked on a selection, then it is the selection that is being dragged. Otherwise, it is the first element, going up the ancestor chain, starting at the node that the user tried to drag, that has the DOM attribute draggable set to true. If there is no such element, then nothing is being dragged, the drag-and-drop operation is never started, and the user agent must not continue with this algorithm.

img elements and a elements with an href attribute have their draggable attribute set to true by default.

If the user agent determines that something can be dragged, a dragstart event must then be fired.

If it is a selection that is being dragged, then this event must be fired on the node that the user started the drag on (typically the text node that the user originally clicked). If the user did not specify a particular node, for example if the user just told the user agent to begin a drag of "the selection", then the event must be fired on the deepest node that is a common ancestor of all parts of the selection.

We should look into how browsers do other types (e.g. Firefox apparently also adds text/html for internal drag and drop of a selection).

If it is not a selection that is being dragged, then the event must be fired on the element that is being dragged.

The node on which the event is fired is the source node. Multiple events are fired on this node during the course of the drag-and-drop operation.

If it is a selection that is being dragged, the dataTransfer member of the event must be created with no nodes. Otherwise, it must be created containing just the source node. Script can use the addElement() method to add further elements to the list of what is being dragged.

If it is a selection that is being dragged, the dataTransfer member of the event must have the text of the selection added to it as the data associated with the text/plain format. Otherwise, if it is an img element being dragged, then the value of the element's src DOM attribute must be added, associated with the text/uri-list format. Otherwise, if it is an a element being dragged, then the value of the element's href DOM attribute must be added, associated with the text/uri-list format. Otherwise, no data is added to the object by the user agent.

If the event is canceled, then the drag-and-drop operation must not occur; the user agent must not continue with this algorithm.

If it is not canceled, then the drag-and-drop operation must be initiated.

Since events with no event handlers registered are, almost by definition, never canceled, drag-and-drop is always available to the user if the author does not specifically prevent it.

The drag-and-drop feedback must be generated from the first of the following sources that is available:

  1. The element specified in the last call to the setDragImage() method of the dataTransfer object of the dragstart event, if the method was called. In visual media, if this is used, the x and y arguments that were passed to that method should be used as hints for where to put the cursor relative to the resulting image. The values are expressed as distances in CSS pixels from the left side and from the top side of the image respectively. [CSS21]
  2. The elements that were added to the dataTransfer object, both before the event was fired, and during the handling of the event using the addElement() method, if any such elements were indeed added.
  3. The selection that the user is dragging.

The user agent must take a note of the data that was placed in the dataTransfer object. This data will be made available again when the drop event is fired.

From this point until the end of the drag-and-drop operation, device input events (e.g. mouse and keyboard events) must be suppressed. In addition, the user agent must track all DOM changes made during the drag-and-drop operation, and add them to its undo history as one atomic operation once the drag-and-drop operation has ended.

During the drag operation, the element directly indicated by the user as the drop target is called the immediate user selection. (Only elements can be selected by the user; other nodes must not be made available as drop targets.) However, the immediate user selection is not necessarily the current target element, which is the element currently selected for the drop part of the drag-and-drop operation. The immediate user selection changes as the user selects different elements (either by pointing at them with a pointing device, or by selecting them in some other way). The current target element changes when the immediate user selection changes, based on the results of event handlers in the document, as described below.

Both the current target element and the immediate user selection can be null, which means no target element is selected. They can also both be elements in other (DOM-based) documents, or other (non-Web) programs altogether. (For example, a user could drag text to a word-processor.) The current target element is initially null.

In addition, there is also a current drag operation, which can take on the values "none", "copy", "link", and "move". Initially, it has the value "none". It is updated by the user agent as described in the steps below.

User agents must, every 350ms (±200ms), perform the following steps in sequence. (If the user agent is still performing the previous iteration of the sequence when the next iteration becomes due, the user agent must not execute the overdue iteration, effectively "skipping missed frames" of the drag-and-drop operation.)

  1. First, the user agent must fire a drag event at the source node. If this event is canceled, the user agent must set the current drag operation to none (no drag operation).

  2. Next, if the drag event was not canceled and the user has not ended the drag-and-drop operation, the user agent must check the state of the drag-and-drop operation, as follows:

    1. First, if the user is indicating a different immediate user selection than during the last iteration (or if this is the first iteration), and if this immediate user selection is not the same as the current target element, then the current target element must be updated, as follows:

      1. If the new immediate user selection is null, or is in a non-DOM document or application, then set the current target element to the same value.

      2. Otherwise, the user agent must fire a dragenter event at the immediate user selection.

      3. If the event is canceled, then the current target element must be set to the immediate user selection.

      4. Otherwise, if the current target element is not the body element, the user agent must fire a dragenter event at the body element, and the current target element must be set to the body element, regardless of whether that event was canceled or not. (If the body element is null, then the current target element would be set to null too in this case, it wouldn't be set to the Document object.)

    2. If the previous step caused the current target element to change, and if the previous target element was not null or a part of a non-DOM document, the user agent must fire a dragleave event at the previous target element.

    3. If the current target element is a DOM element, the user agent must fire a dragover event at this current target element.

      If the dragover event is not canceled, the current drag operation must be reset to "none".

      Otherwise, the current drag operation must be set based on the values the effectAllowed and dropEffect attributes of the dataTransfer object had after the event was handled, as per the following table:

      effectAllowed dropEffect Drag operation
      uninitialized, copy, copyLink, copyMove, or all copy "copy"
      uninitialized, link, copyLink, linkMove, or all link "link"
      uninitialized, move, copyMove, linkMove, or all move "move"
      Any other case "none"

      Then, regardless of whether the dragover event was canceled or not, the drag feedback (e.g. the mouse cursor) must be updated to match the current drag operation, as follows:

      Drag operation Feedback
      "copy" Data will be copied if dropped here.
      "link" Data will be linked if dropped here.
      "move" Data will be moved if dropped here.
      "none" No operation allowed, dropping here will cancel the drag-and-drop operation.
    4. Otherwise, if the current target element is not a DOM element, the user agent must use platform-specific mechanisms to determine what drag operation is being performed (none, copy, link, or move). This sets the current drag operation.

  3. Otherwise, if the user ended the drag-and-drop operation (e.g. by releasing the mouse button in a mouse-driven drag-and-drop interface), or if the drag event was canceled, then this will be the last iteration. The user agent must execute the following steps, then stop looping.

    1. If the current drag operation is none (no drag operation), or, if the user ended the drag-and-drop operation by canceling it (e.g. by hitting the Escape key), or if the current target element is null, then the drag operation failed. If the current target element is a DOM element, the user agent must fire a dragleave event at it; otherwise, if it is not null, it must use platform-specific conventions for drag cancellation.

    2. Otherwise, the drag operation was as success. If the current target element is a DOM element, the user agent must fire a drop event at it; otherwise, it must use platform-specific conventions for indicating a drop.

      When the target is a DOM element, the dropEffect attribute of the event's dataTransfer object must be given the value representing the current drag operation (copy, link, or move), and the object must be set up so that the getData() method will return the data that was added during the dragstart event.

      If the event is canceled, the current drag operation must be set to the value of the dropEffect attribute of the event's dataTransfer object as it stood after the event was handled.

      Otherwise, the event is not canceled, and the user agent must perform the event's default action, which depends on the exact target as follows:

      If the current target element is a text field (e.g. textarea, or an input element whose type attribute is in the Text state)
      The user agent must insert the data associated with the text/plain format, if any, into the text field in a manner consistent with platform-specific conventions (e.g. inserting it at the current mouse cursor position, or inserting it at the end of the field).
      Otherwise
      Reset the current drag operation to "none".
    3. Finally, the user agent must fire a dragend event at the source node, with the dropEffect attribute of the event's dataTransfer object being set to the value corresponding to the current drag operation.

      The current drag operation can change during the processing of the drop event, if one was fired.

      The event is not cancelable. After the event has been handled, the user agent must act as follows:

      If the current target element is a text field (e.g. textarea, or an input element whose type attribute is in the Text state), and a drop event was fired in the previous step, and the current drag operation is "move", and the source of the drag-and-drop operation is a selection in the DOM
      The user agent should delete the range representing the dragged selection from the DOM.
      If the current target element is a text field (e.g. textarea, or an input element whose type attribute is in the Text state), and a drop event was fired in the previous step, and the current drag operation is "move", and the source of the drag-and-drop operation is a selection in a text field
      The user agent should delete the dragged selection from the relevant text field.
      Otherwise
      The event has no default action.
6.9.4.1 When the drag-and-drop operation starts or ends in another document

The model described above is independent of which Document object the nodes involved are from; the events must be fired as described above and the rest of the processing model must be followed as described above, irrespective of how many documents are involved in the operation.

6.9.4.2 When the drag-and-drop operation starts or ends in another application

If the drag is initiated in another application, the source node is not a DOM node, and the user agent must use platform-specific conventions instead when the requirements above involve the source node. User agents in this situation must act as if the dragged data had been added to the DataTransfer object when the drag started, even though no dragstart event was actually fired; user agents must similarly use platform-specific conventions when deciding on what drag feedback to use.

If a drag is started in a document but ends in another application, then the user agent must instead replace the parts of the processing model relating to handling the target according to platform-specific conventions.

In any case, scripts running in the context of the document must not be able to distinguish the case of a drag-and-drop operation being started or ended in another application from the case of a drag-and-drop operation being started or ended in another document from another domain.

6.9.5 The draggable attribute

All elements may have the draggable content attribute set. The draggable attribute is an enumerated attribute. It has three states. The first state is true and it has the keyword true. The second state is false and it has the keyword false. The third state is auto; it has no keywords but it is the missing value default.

The true state means the element is draggable; the false state means that it is not. The auto state uses the default behavior of the user agent.

element . draggable [ = value ]

Returns true if the element is draggable; otherwise, returns false.

Can be set, to override the default and set the draggable content attribute.

The draggable DOM attribute, whose value depends on the content attribute's in the way described below, controls whether or not the element is draggable. Generally, only text selections are draggable, but elements whose draggable DOM attribute is true become draggable as well.

If an element's draggable content attribute has the state true, the draggable DOM attribute must return true.

Otherwise, if the element's draggable content attribute has the state false, the draggable DOM attribute must return false.

Otherwise, the element's draggable content attribute has the state auto. If the element is an img element, or, if the element is an a element with an href content attribute, the draggable DOM attribute must return true.

Otherwise, the draggable DOM must return false.

If the draggable DOM attribute is set to the value false, the draggable content attribute must be set to the literal value false. If the draggable DOM attribute is set to the value true, the draggable content attribute must be set to the literal value true.

6.9.6 Copy and paste

Copy-and-paste is a form of drag-and-drop: the "copy" part is equivalent to dragging content to another application (the "clipboard"), and the "paste" part is equivalent to dragging content from another application.

Select-and-paste (a model used by mouse operations in the X Window System) is equivalent to a drag-and-drop operation where the source is the selection.

6.9.6.1 Copy to clipboard

When the user invokes a copy operation, the user agent must act as if the user had invoked a drag on the current selection. If the drag-and-drop operation initiates, then the user agent must act as if the user had indicated (as the immediate user selection) a hypothetical application representing the clipboard. Then, the user agent must act as if the user had ended the drag-and-drop operation without canceling it. If the drag-and-drop operation didn't get canceled, the user agent should then follow the relevant platform-specific conventions for copy operations (e.g. updating the clipboard).

6.9.6.2 Cut to clipboard

When the user invokes a cut operation, the user agent must act as if the user had invoked a copy operation (see the previous section), followed, if the copy was completed successfully, by a selection delete operation.

6.9.6.3 Paste from clipboard

When the user invokes a clipboard paste operation, the user agent must act as if the user had invoked a drag on a hypothetical application representing the clipboard, setting the data associated with the drag as the content on the clipboard (in whatever formats are available).

Then, the user agent must act as if the user had indicated (as the immediate user selection) the element with the keyboard focus, and then ended the drag-and-drop operation without canceling it.

6.9.6.4 Paste from selection

When the user invokes a selection paste operation, the user agent must act as if the user had invoked a drag on the current selection, then indicated (as the immediate user selection) the element with the keyboard focus, and then ended the drag-and-drop operation without canceling it.

6.9.7 Security risks in the drag-and-drop model

User agents must not make the data added to the DataTransfer object during the dragstart event available to scripts until the drop event, because otherwise, if a user were to drag sensitive information from one document to a second document, crossing a hostile third document in the process, the hostile document could intercept the data.

For the same reason, user agents must consider a drop to be successful only if the user specifically ended the drag operation — if any scripts end the drag operation, it must be considered unsuccessful (canceled) and the drop event must not be fired.

User agents should take care to not start drag-and-drop operations in response to script actions. For example, in a mouse-and-window environment, if a script moves a window while the user has his mouse button depressed, the UA would not consider that to start a drag. This is important because otherwise UAs could cause data to be dragged from sensitive sources and dropped into hostile documents without the user's consent.

6.10 Undo history

There has got to be a better way of doing this, surely.

6.10.1 Introduction

...

6.10.2 Definitions

The user agent must associate an undo transaction history with each HTMLDocument object.

The undo transaction history is a list of entries. The entries are of two type: DOM changes and undo objects.

Each DOM changes entry in the undo transaction history consists of batches of one or more of the following:

Undo object entries consist of objects representing state that scripts running in the document are managing. For example, a Web mail application could use an undo object to keep track of the fact that a user has moved an e-mail to a particular folder, so that the user can undo the action and have the e-mail return to its former location.

Broadly speaking, DOM changes entries are handled by the UA in response to user edits of form controls and editing hosts on the page, and undo object entries are handled by script in response to higher-level user actions (such as interactions with server-side state, or in the implementation of a drawing tool).

6.10.3 The UndoManager interface

This API sucks. Seriously. It's a terrible API. Really bad. I hate it. Here are the requirements:

To manage undo object entries in the undo transaction history, the UndoManager interface can be used:

interface UndoManager {
  readonly attribute unsigned long length;
  [IndexGetter] any item(in unsigned long index);
  readonly attribute unsigned long position;
  unsigned long add(in any data, in DOMString title);
  void remove(in unsigned long index);
  void clearUndo();
  void clearRedo();
};
window . undoManager

Returns the UndoManager object.

undoManager . length

Returns the number of entries in the undo history.

data = undoManager . item(index)
undoManager[index]

Returns the entry with index index in the undo history.

Returns null if index is out of range.

undoManager . position

Returns the number of the current entry in the undo history. (Entries at and past this point are redo entries.)

undoManager . add(data, title)

Adds the specified entry to the undo history.

undoManager . remove(index)

Removes the specified entry to the undo history.

Throws an INDEX_SIZE_ERR exception if the given index is out of range.

undoManager . clearUndo()

Removes all entries before the current position in the undo history.

undoManager . clearRedo()

Removes all entries at and after the current position in the undo history.

The undoManager attribute of the Window interface must return the object implementing the UndoManager interface for that Window object's associated HTMLDocument object.

UndoManager objects represent their document's undo transaction history. Only undo object entries are visible with this API, but this does not mean that DOM changes entries are absent from the undo transaction history.

The length attribute must return the number of undo object entries in the undo transaction history. This is the length.

The object's indices of the supported indexed properties are the numbers in the range zero to length-1, unless the length is zero, in which case there are no supported indexed properties.

The item(n) method must return the nth undo object entry in the undo transaction history.

The undo transaction history has a current position. This is the position between two entries in the undo transaction history's list where the previous entry represents what needs to happen if the user invokes the "undo" command (the "undo" side, lower numbers), and the next entry represents what needs to happen if the user invokes the "redo" command (the "redo" side, higher numbers).

The position attribute must return the index of the undo object entry nearest to the undo position, on the "redo" side. If there are no undo object entries on the "redo" side, then the attribute must return the same as the length attribute. If there are no undo object entries on the "undo" side of the undo position, the position attribute returns zero.

Since the undo transaction history contains both undo object entries and DOM changes entries, but the position attribute only returns indices relative to undo object entries, it is possible for several "undo" or "redo" actions to be performed without the value of the position attribute changing.

The add(data, title) method's behavior depends on the current state. Normally, it must insert the data object passed as an argument into the undo transaction history immediately before the undo position, optionally remembering the given title to use in the UI. If the method is called during an undo operation, however, the object must instead be added immediately after the undo position.

If the method is called and there is neither an undo operation in progress nor a redo operation in progress then any entries in the undo transaction history after the undo position must be removed (as if clearRedo() had been called).

We could fire events when someone adds something to the undo history -- one event per undo object entry before the position (or after, during redo addition), allowing the script to decide if that entry should remain or not. Or something. Would make it potentially easier to expire server-held state when the server limitations come into play.

The remove(index) method must remove the undo object entry with the specified index. If the index is less than zero or greater than or equal to length then the method must raise an INDEX_SIZE_ERR exception. DOM changes entries are unaffected by this method.

The clearUndo() method must remove all entries in the undo transaction history before the undo position, be they DOM changes entries or undo object entries.

The clearRedo() method must remove all entries in the undo transaction history after the undo position, be they DOM changes entries or undo object entries.

Another idea is to have a way for scripts to say "startBatchingDOMChangesForUndo()" and after that the changes to the DOM go in as if the user had done them.

6.10.4 Undo: moving back in the undo transaction history

When the user invokes an undo operation, or when the execCommand() method is called with the undo command, the user agent must perform an undo operation.

If the undo position is at the start of the undo transaction history, then the user agent must do nothing.

If the entry immediately before the undo position is a DOM changes entry, then the user agent must remove that DOM changes entry, reverse the DOM changes that were listed in that entry, and, if the changes were reversed with no problems, add a new DOM changes entry (consisting of the opposite of those DOM changes) to the undo transaction history on the other side of the undo position.

If the DOM changes cannot be undone (e.g. because the DOM state is no longer consistent with the changes represented in the entry), then the user agent must simply remove the DOM changes entry, without doing anything else.

If the entry immediately before the undo position is an undo object entry, then the user agent must first remove that undo object entry from the undo transaction history, and then must fire an undo event at the Window object, using the undo object entry's associated undo object as the event's data.

Any calls to add() while the event is being handled will be used to populate the redo history, and will then be used if the user invokes the "redo" command to undo his undo.

6.10.5 Redo: moving forward in the undo transaction history

When the user invokes a redo operation, or when the execCommand() method is called with the redo command, the user agent must perform a redo operation.

This is mostly the opposite of an undo operation, but the full definition is included here for completeness.

If the undo position is at the end of the undo transaction history, then the user agent must do nothing.

If the entry immediately after the undo position is a DOM changes entry, then the user agent must remove that DOM changes entry, reverse the DOM changes that were listed in that entry, and, if the changes were reversed with no problems, add a new DOM changes entry (consisting of the opposite of those DOM changes) to the undo transaction history on the other side of the undo position.

If the DOM changes cannot be redone (e.g. because the DOM state is no longer consistent with the changes represented in the entry), then the user agent must simply remove the DOM changes entry, without doing anything else.

If the entry immediately after the undo position is an undo object entry, then the user agent must first remove that undo object entry from the undo transaction history, and then must fire a redo event at the Window object, using the undo object entry's associated undo object as the event's data.

6.10.6 The UndoManagerEvent interface and the undo and redo events

interface UndoManagerEvent : Event {
  readonly attribute any data;
  void initUndoManagerEvent(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in any dataArg);
  void initUndoManagerEventNS(in DOMString namespaceURIArg, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in any dataArg);
};
event . data

Returns the data that was passed to the add() method.

The initUndoManagerEvent() and initUndoManagerEventNS() methods must initialize the event in a manner analogous to the similarly-named methods in the DOM3 Events interfaces. [DOM3EVENTS]

The data attribute represents the undo object for the event.

The undo and redo events do not bubble, cannot be canceled, and have no default action. When the user agent fires one of these events it must use the UndoManagerEvent interface, with the data field containing the relevant undo object.

6.10.7 Implementation notes

How user agents present the above conceptual model to the user is not defined. The undo interface could be a filtered view of the undo transaction history, it could manipulate the undo transaction history in ways not described above, and so forth. For example, it is possible to design a UA that appears to have separate undo transaction histories for each form control; similarly, it is possible to design systems where the user has access to more undo information than is present in the official (as described above) undo transaction history (such as providing a tree-based approach to document state). Such UI models should be based upon the single undo transaction history described in this section, however, such that to a script there is no detectable difference.

6.11 Command APIs

document . execCommand(commandId [, showUI [, value ] ] )

Runs the action specified by the first argument, as described in the list below. The second and third arguments sometimes affect the action. (If they don't they are ignored.)

document . queryCommandEnabled(commandId)

Returns whether the given command is enabled, as described in the list below.

document . queryCommandIndeterm(commandId)

Returns whether the given command is indeterminate, as described in the list below.

document . queryCommandState(commandId)

Returns the state of the command, as described in the list below.

document . queryCommandSupported(commandId)

Returns true if the command is supported; otherwise, returns false.

document . queryCommandValue(commandId)

Returns the value of the command, as described in the list below.

The execCommand(commandId, showUI, value) method on the HTMLDocument interface allows scripts to perform actions on the current selection or at the current caret position. Generally, these commands would be used to implement editor UI, for example having a "delete" button on a toolbar.

There are three variants to this method, with one, two, and three arguments respectively. The showUI and value parameters, even if specified, are ignored unless otherwise stated.

When execCommand() is invoked, the user agent must follow the following steps:

  1. If the given commandId maps to an entry in the list below whose "Enabled When" entry has a condition that is currently false, do nothing; abort these steps.
  2. Otherwise, execute the "Action" listed below for the given commandId.

A document is ready for editing host commands if it has a selection that is entirely within an editing host, or if it has no selection but its caret is inside an editing host.

The queryCommandEnabled(commandId) method, when invoked, must return true if the condition listed below under "Enabled When" for the given commandId is true, and false otherwise.

The queryCommandIndeterm(commandId) method, when invoked, must return true if the condition listed below under "Indeterminate When" for the given commandId is true, and false otherwise.

The queryCommandState(commandId) method, when invoked, must return the value expressed below under "State" for the given commandId.

The queryCommandSupported(commandId) method, when invoked, must return true if the given commandId is in the list below, and false otherwise.

The queryCommandValue(commandId) method, when invoked, must return the value expressed below under "Value" for the given commandId.

The possible values for commandId, and their corresponding meanings, are as follows. These values must be compared to the argument in an ASCII case-insensitive manner.

bold
Summary: Toggles whether the selection is bold.
Action: The user agent must act as if the user had requested that the selection be wrapped in the semantics of the b element (or, again, unwrapped, or have that semantic inserted or removed, as defined by the UA).
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: True if the selection, or the caret, if there is no selection, is, or is contained within, a b element. False otherwise.
Value: The string "true" if the expression given for the "State" above is true, the string "false" otherwise.
createLink
Summary: Toggles whether the selection is a link or not. If the second argument is true, and a link is to be added, the user agent will ask the user for the address. Otherwise, the third argument will be used as the address.
Action: The user agent must act as if the user had requested that the selection be wrapped in the semantics of the a element (or, again, unwrapped, or have that semantic inserted or removed, as defined by the UA). If the user agent creates an a element or modifies an existing a element, then if the showUI argument is present and has the value false, then the value of the value argument must be used as the URL of the link. Otherwise, the user agent should prompt the user for the URL of the link.
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
delete
Summary: Deletes the selection or the character before the cursor.
Action: The user agent must act as if the user had performed a backspace operation.
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
formatBlock
Summary: Wraps the selection in the element given by the second argument. If the second argument doesn't specify an element that is flow content but not phrasing content, does nothing.

Action: The user agent must run the following steps:

  1. If the value argument wasn't specified, abort these steps without doing anything.

  2. If the value argument has a leading U+003C LESS-THAN SIGN character ('<') and a trailing U+003E GREATER-THAN SIGN character ('>'), then remove the first and last characters from value.

  3. If value is (now) an ASCII case-insensitive match for the tag name of an element defined by this specification that is defined to be flow content but not phrasing content, then, for every position in the selection, take the furthest flow content ancestor element of that position that contains only phrasing content, and, if that element is editable, and has a content model that allows it to contain flow content other than phrasing content, and has a parent element whose content model allows that parent to contain any flow content, replace the element with one in the HTML namespace whose name is value, and move all the children that were in the element to the new element.

    If there is no selection, then, where in the description above refers to the selection, the user agent must act as if the selection was an empty range (with just one position) at the caret position.

Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
forwardDelete
Summary: Deletes the selection or the character after the cursor.
Action: The user agent must act as if the user had performed a forward delete operation.
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
insertImage
Summary: Toggles whether the selection is an image or not. If the second argument is true, and an image is to be added, the user agent will ask the user for the address. Otherwise, the third argument will be used as the address.
Action: The user agent must act as if the user had requested that the selection be wrapped in the semantics of the img element (or, again, unwrapped, or have that semantic inserted or removed, as defined by the UA). If the user agent creates an img element or modifies an existing img element, then if the showUI argument is present and has the value false, then the value of the value argument must be used as the URL of the image. Otherwise, the user agent should prompt the user for the URL of the image.
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
insertHTML
Summary: Replaces the selection with the value of the third argument parsed as HTML.

Action: The user agent must run the following steps:

  1. If the document is an XML document, then throw an INVALID_ACCESS_ERR exception and abort these steps.

  2. If the value argument wasn't specified, abort these steps without doing anything.

  3. If there is a selection, act as if the user had requested that the selection be deleted.

  4. Invoke the HTML fragment parsing algorithm with an arbitrary orphan body element owned by the same Document as the context element and with the value argument as input.

  5. Insert the nodes returned by the previous step into the document at the location of the caret, firing any mutation events as appropriate.

Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
insertLineBreak
Summary: Inserts a line break.
Action: The user agent must act as if the user had requested a line separator.
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
insertOrderedList
Summary: Toggles whether the selection is an ordered list.
Action: The user agent must act as if the user had requested that the selection be wrapped in the semantics of the ol element (or unwrapped, or, if there is no selection, have that semantic inserted or removed — the exact behavior is UA-defined).
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
insertUnorderedList
Summary: Toggles whether the selection is an unordered list.
Action: The user agent must act as if the user had requested that the selection be wrapped in the semantics of the ul element (or unwrapped, or, if there is no selection, have that semantic inserted or removed — the exact behavior is UA-defined).
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
insertParagraph
Summary: Inserts a paragraph break.
Action: The user agent must act as if the user had performed a break block editing action.
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
insertText
Summary: Inserts the text given in the third parameter.
Action: The user agent must act as if the user had inserted text corresponding to the value parameter.
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
italic
Summary: Toggles whether the selection is italic.
Action: The user agent must act as if the user had requested that the selection be wrapped in the semantics of the i element (or, again, unwrapped, or have that semantic inserted or removed, as defined by the UA).
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: True if the selection, or the caret, if there is no selection, is, or is contained within, a i element. False otherwise.
Value: The string "true" if the expression given for the "State" above is true, the string "false" otherwise.
redo
Summary: Acts as if the user had requested a redo.
Action: The user agent must move forward one step in its undo transaction history, restoring the associated state. If the undo position is at the end of the undo transaction history, the user agent must do nothing. See the undo history.
Enabled When: The undo position is not at the end of the undo transaction history.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
selectAll
Summary: Selects all the editable content.
Action: The user agent must change the selection so that all the content in the currently focused editing host is selected. If no editing host is focused, then the content of the entire document must be selected.
Enabled When: Always.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
subscript
Summary: Toggles whether the selection is subscripted.
Action: The user agent must act as if the user had requested that the selection be wrapped in the semantics of the sub element (or, again, unwrapped, or have that semantic inserted or removed, as defined by the UA).
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: True if the selection, or the caret, if there is no selection, is, or is contained within, a sub element. False otherwise.
Value: The string "true" if the expression given for the "State" above is true, the string "false" otherwise.
superscript
Summary: Toggles whether the selection is superscripted.
Action: The user agent must act as if the user had requested that the selection be wrapped in the semantics of the sup element (or unwrapped, or, if there is no selection, have that semantic inserted or removed — the exact behavior is UA-defined).
Enabled When: The document is ready for editing host commands.
Indeterminate When: Never.
State: True if the selection, or the caret, if there is no selection, is, or is contained within, a sup element. False otherwise.
Value: The string "true" if the expression given for the "State" above is true, the string "false" otherwise.
undo
Summary: Acts as if the user had requested an undo.
Action: The user agent must move back one step in its undo transaction history, restoring the associated state. If the undo position is at the start of the undo transaction history, the user agent must do nothing. See the undo history.
Enabled When: The undo position is not at the start of the undo transaction history.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
unlink
Summary: Removes all links from the selection.
Action: The user agent must remove all a elements that have href attributes and that are partially or completely included in the current selection.
Enabled When: The document has a selection that is entirely within an editing host and that contains (either partially or completely) at least one a element that has an href attribute.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
unselect
Summary: Unselects everything.
Action: The user agent must change the selection so that nothing is selected.
Enabled When: Always.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".
vendorID-customCommandID
Action: User agents may implement vendor-specific extensions to this API. Vendor-specific extensions to the list of commands should use the syntax vendorID-customCommandID so as to prevent clashes between extensions from different vendors and future additions to this specification.
Enabled When: UA-defined.
Indeterminate When: UA-defined.
State: UA-defined.
Value: UA-defined.
Anything else
Action: User agents must do nothing.
Enabled When: Never.
Indeterminate When: Never.
State: Always false.
Value: Always the string "false".

7 Communication

7.1 Event definitions

Messages in server-sent events, Web sockets, cross-document messaging, and channel messaging use the message event.

The following interface is defined for this event:

interface MessageEvent : Event {
  readonly attribute any data;
  readonly attribute DOMString origin;
  readonly attribute DOMString lastEventId;
  readonly attribute WindowProxy source;
  readonly attribute MessagePortArray ports;
  void initMessageEvent(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in any dataArg, in DOMString originArg, in DOMString lastEventIdArg, in WindowProxy sourceArg, in MessagePortArray portsArg);
  void initMessageEventNS(in DOMString namespaceURI, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in any dataArg, in DOMString originArg, in DOMString lastEventIdArg, in WindowProxy sourceArg, in MessagePortArray portsArg);
};
event . data

Returns the data of the message.

event . origin

Returns the origin of the message, for server-sent events and cross-document messaging.

event . lastEventId

Returns the last event ID, for server-sent events.

event . source

Returns the WindowProxy of the source window, for cross-document messaging.

event . ports

Returns the MessagePortArray sent with the message, for cross-document messaging and channel messaging.

The initMessageEvent() and initMessageEventNS() methods must initialize the event in a manner analogous to the similarly-named methods in the DOM3 Events interfaces. [DOM3EVENTS]

The data attribute represents the message being sent.

The origin attribute represents, in server-sent events and cross-document messaging, the origin of the document that sent the message (typically the scheme, hostname, and port of the document, but not its path or fragment identifier).

The lastEventId attribute represents, in server-sent events, the last event ID string of the event source.

The source attribute represents, in cross-document messaging, the WindowProxy of the browsing context of the Window object from which the message came.

The ports attribute represents, in cross-document messaging and channel messaging the MessagePortArray being sent, if any.

Unless otherwise specified, when the user agent creates and dispatches a message event in the algorithms described in the following sections, the lastEventId attribute must be the empty string, the origin attribute must be the empty string, the source attribute must be null, and the ports attribute must be null.

7.2 Cross-document messaging

Web browsers, for security and privacy reasons, prevent documents in different domains from affecting each other; that is, cross-site scripting is disallowed.

While this is an important security feature, it prevents pages from different domains from communicating even when those pages are not hostile. This section introduces a messaging system that allows documents to communicate with each other regardless of their source domain, in a way designed to not enable cross-site scripting attacks.

The task source for the tasks in cross-document messaging is the posted message task source.

7.2.1 Introduction

This section is non-normative.

For example, if document A contains an iframe element that contains document B, and script in document A calls postMessage() on the Window object of document B, then a message event will be fired on that object, marked as originating from the Window of document A. The script in document A might look like:

var o = document.getElementsByTagName('iframe')[0];
o.contentWindow.postMessage('Hello world', 'http://b.example.org/');

To register an event handler for incoming events, the script would use addEventListener() (or similar mechanisms). For example, the script in document B might look like:

window.addEventListener('message', receiver, false);
function receiver(e) {
  if (e.origin == 'http://example.com') {
    if (e.data == 'Hello world') {
      e.source.postMessage('Hello', e.origin);
    } else {
      alert(e.data);
    }
  }
}

This script first checks the domain is the expected domain, and then looks at the message, which it either displays to the user, or responds to by sending a message back to the document which sent the message in the first place.

7.2.2 Security

7.2.2.1 Authors

Use of this API requires extra care to protect users from hostile entities abusing a site for their own purposes.

Authors should check the origin attribute to ensure that messages are only accepted from domains that they expect to receive messages from. Otherwise, bugs in the author's message handling code could be exploited by hostile sites.

Furthermore, even after checking the origin attribute, authors should also check that the data in question is of the expected format. Otherwise, if the source of the event has been attacked using a cross-site scripting flaw, further unchecked processing of information sent using the postMessage() method could result in the attack being propagated into the receiver.

Authors should not use the wildcard keyword ("*") in the targetOrigin argument in messages that contain any confidential information, as otherwise there is no way to guarantee that the message is only delivered to the recipient to which it was intended.

7.2.2.2 User agents

The integrity of this API is based on the inability for scripts of one origin to post arbitrary events (using dispatchEvent() or otherwise) to objects in other origins (those that are not the same).

Implementors are urged to take extra care in the implementation of this feature. It allows authors to transmit information from one domain to another domain, which is normally disallowed for security reasons. It also requires that UAs be careful to allow access to certain properties but not others.

7.2.3 Posting messages

window . postMessage(message, [ ports, ] targetOrigin)

Posts a message, optionally with an array of ports, to the given window.

If the origin of the target window doesn't match the given origin, the message is discarded, to avoid information leakage. To send the message to the target regardless of origin, set the target origin to "*".

Throws an INVALID_STATE_ERR if the ports array is not null and it contains either null entries, duplicate ports, or ports that are not entangled.

When a script invokes the postMessage(message, targetOrigin) method (with only two arguments) on a Window object, the user agent must follow these steps:

  1. If the value of the targetOrigin argument is not a single U+002A ASTERISK character ("*"), and resolving it relative to the first script's base URL either fails or results in a URL with a <host-specific> component that is neither empty nor a single U+002F SOLIDUS character (/), then throw a SYNTAX_ERR exception and abort the overall set of steps.

  2. Let message clone be the result of obtaining a structured clone of the message argument. If this throws an exception, then throw that exception and abort these steps.

  3. Return from the postMessage() method, but asynchronously continue running these steps.

  4. If the targetOrigin argument has a value other than a single literal U+002A ASTERISK character ("*"), and the Document of the Window object on which the method was invoked does not have the same origin as targetOrigin, then abort these steps silently.

  5. Create an event that uses the MessageEvent interface, with the event name message, which does not bubble, is not cancelable, and has no default action. The data attribute must be set to the value of message clone, the origin attribute must be set to the Unicode serialization of the origin of the script that invoked the method, and the source attribute must be set to the script's global object.

  6. Queue a task to dispatch the event created in the previous step at the Window object on which the method was invoked. The task source for this task is the posted message task source.

7.2.4 Posting messages with message ports

When a script invokes the postMessage(message, ports, targetOrigin) method (with three arguments) on a Window object, the user agent must follow these steps:

  1. If the value of the targetOrigin argument is not a single U+002A ASTERISK character ("*"), and resolving it relative to the first script's base URL either fails or results in a URL with a <host-specific> component that is neither empty nor a single U+002F SOLIDUS character (/), then throw a SYNTAX_ERR exception and abort the overall set of steps.

  2. Let message clone be the result of obtaining a structured clone of the message argument. If this throws an exception, then throw that exception and abort these steps.

  3. If the ports argument is null, then act as if the method had just been called with two arguments, message and targetOrigin.

  4. If any of the entries in ports are null, if any of the entries in ports are not entangled MessagePort objects, or if any MessagePort object is listed in ports more than once, then throw an INVALID_STATE_ERR exception.

  5. Let new ports be an empty array.

    For each port in ports in turn, obtain a new port by cloning the port with the Window object on which the method was invoked as the owner of the clone, and append the clone to the new ports array.

    If the original ports array was empty, then the new ports array will also be empty.

  6. Return from the postMessage() method, but asynchronously continue running these steps.

  7. If the targetOrigin argument has a value other than a single literal U+002A ASTERISK character ("*"), and the Document of the Window object on which the method was invoked does not have the same origin as targetOrigin, then abort these steps silently.

  8. Create an event that uses the MessageEvent interface, with the event name message, which does not bubble, is not cancelable, and has no default action. The data attribute must be set to the value of message clone, the origin attribute must be set to the Unicode serialization of the origin of the script that invoked the method, and the source attribute must be set to the script's global object.

  9. Let the ports attribute of the event be the new ports array.

  10. Queue a task to dispatch the event created in the previous step at the Window object on which the method was invoked. The task source for this task is the posted message task source.

These steps, with the exception of the second and third steps and the penultimate step, are identical to those in the previous section.

7.3 Channel messaging

7.3.1 Introduction

This section is non-normative.

An introduction to the channel and port APIs.

7.3.2 Message channels

[Constructor]
interface MessageChannel {
  readonly attribute MessagePort port1;
  readonly attribute MessagePort port2;
};
channel = new MessageChannel()

Returns a new MessageChannel object with two new MessagePort objects.

channel . port1

Returns the first MessagePort object.

channel . port2

Returns the second MessagePort object.

When the MessageChannel() constructor is called, it must run the following algorithm:

  1. Create a new MessagePort object owned by the script's global object, and let port1 be that object.

  2. Create a new MessagePort object owned by the script's global object, and let port2 be that object.

  3. Entangle the port1 and port2 objects.

  4. Instantiate a new MessageChannel object, and let channel be that object.

  5. Let the port1 attribute of the channel object be port1.

  6. Let the port2 attribute of the channel object be port2.

  7. Return channel.

The port1 and port2 attributes must return the values they were assigned when the MessageChannel object was created.

7.3.3 Message ports

Each channel has two message ports. Data sent through one port is received by the other port, and vice versa.

typedef sequence<MessagePort> MessagePortArray;

interface MessagePort {
  readonly attribute boolean active;
  void postMessage(in any message, [Optional] in MessagePortArray ports);
  void start();
  void close();

  // event handler attributes
           attribute Function onmessage;
};
port . active

Returns true if the port is still active; otherwise, returns false.

port . postMessage(message [, ports] )

Posts a message through the channel, optionally with the given ports.

Throws an INVALID_STATE_ERR if the ports array is not null and it contains either null entries, duplicate ports, ports that are not entangled, or the source or target port.

port . start()

Begins dispatching messages received on the port.

port . close()

Disconnects the port, so that it is no longer active.

Objects implementing the MessagePort interface must also implement the EventTarget interface.

Each MessagePort object can be entangled with another (a symmetric relationship). Each MessagePort object also has a task source called the port message queue, initial empty. A port message queue can be open or closed, and is initially closed.

When the user agent is to create a new MessagePort object owned by a script's global object object owner, it must instantiate a new MessagePort object, and let its owner be owner.


When the user agent is to entangle two MessagePort objects, it must run the following steps:

  1. If one of the ports is already entangled, then disentangle it and the port that it was entangled with.

    If those two previously entangled ports were the two ports of a MessageChannel object, then that MessageChannel object no longer represents an actual channel: the two ports in that object are no longer entangled.

  2. Associate the two ports to be entangled, so that they form the two parts of a new channel. (There is no MessageChannel object that represents this channel.)


When the user agent is to clone a port original port, with the clone being owned by owner, it must run the following steps, which return either a new MessagePort object or an exception for the caller to raise. These steps must be run atomically.

  1. If the original port is not entangled without another port, then return an INVALID_STATE_ERR exception and abort all these steps.

  2. Let the remote port be the port with which the original port is entangled.

  3. Create a new MessagePort object owned by owner, and let new port be that object.

  4. Move all the events in the port message queue of original port to the port message queue of new port, if any, leaving the new port's port message queue in its initial closed state.

  5. Entangle the remote port and new port objects. The original port object will be disentangled by this process.

  6. Return new port. It is the clone.


The active attribute must return true if the port is entangled, and false otherwise.


The postMessage() method, when called on a port source port, must cause the user agent to run the following steps:

  1. Let message be the method's first argument.

  2. Let data port be the method's second argument, if any.

  3. Let message clone be the result of obtaining a structured clone of the message argument. If this throws an exception, then throw that exception and abort these steps.

  4. If the source port is not entangled with another port, then return and abort these steps.

  5. Let target port be the port with which source port is entangled.

  6. Create an event that uses the MessageEvent interface, with the name message, which does not bubble, is not cancelable, and has no default action.

  7. Let the data attribute of the event have the value of message clone.

  8. If the method was called with a second argument ports and that argument isn't null, then run the following substeps:

    1. If any of the entries in ports are null, if any of the entries in ports are not entangled MessagePort objects, or if any MessagePort object is listed in ports more than once, then throw an INVALID_STATE_ERR exception.

    2. Let new ports be an empty array.

      For each port in ports in turn, obtain a new port by cloning the port with the owner of the target port as the owner of the clone, and append the clone to the new ports array.

      If the original ports array was empty, then the new ports array will also be empty.

    3. Let the ports attribute of the event be the new ports array.

  9. Return from the method, but continue with these steps.

  10. Add the event to the port message queue of target port.


The start() method must open its port's port message queue, if it is not already open.

When a port's port message queue is open, the event loop must use it as one of its task sources.

If the Document of the port's event handlers' global object is not fully active, then the messages are lost.


The close() method, when called on a port local port that is entangled with another port, must cause the user agents to disentangle the two ports. If the method is called on a port that is not entangled, then the method must do nothing.


The following are the event handler attributes (and their corresponding event handler event types) that must be supported, as DOM attributes, by all objects implementing the MessagePort interface:

event handler attribute Event handler event type
onmessage message

The first time a MessagePort object's onmessage DOM attribute is set, the port's port message queue must be opened, as if the start() method had been called.

7.3.3.1 Ports and garbage collection

User agents must act as if MessagePort objects have a strong reference to their entangled MessagePort object.

Thus, a message port can be received, given an event listener, and then forgotten, and so long as that event listener could receive a message, the channel will be maintained.

Of course, if this was to occur on both sides of the channel, then both ports would be garbage collected, since they would not be reachable from live code, despite having a strong reference to each other.

Furthermore, a MessagePort object must not be garbage collected while there exists a message in a task queue that is to be dispatched on that MessagePort object, or while the MessagePort object's port message queue is open and there exists a message event in that queue.

8 The HTML syntax

This section only describes the rules for text/html resources. Rules for XML resources are discussed in the section below entitled "The XHTML syntax".

8.1 Writing HTML documents

This section only applies to documents, authoring tools, and markup generators. In particular, it does not apply to conformance checkers; conformance checkers must use the requirements given in the next section ("parsing HTML documents").

Documents must consist of the following parts, in the given order:

  1. Optionally, a single U+FEFF BYTE ORDER MARK (BOM) character.
  2. Any number of comments and space characters.
  3. A DOCTYPE.
  4. Any number of comments and space characters.
  5. The root element, in the form of an html element.
  6. Any number of comments and space characters.

The various types of content mentioned above are described in the next few sections.

In addition, there are some restrictions on how character encoding declarations are to be serialized, as discussed in the section on that topic.

Space characters before the root html element, and space characters at the start of the html element and before the head element, will be dropped when the document is parsed; space characters after the root html element will be parsed as if they were at the end of the body element. Thus, space characters around the root element do not round-trip.

It is suggested that newlines be inserted after the DOCTYPE, after any comments that are before the root element, after the html element's start tag (if it is not omitted), and after any comments that are inside the html element but before the head element.

Many strings in the HTML syntax (e.g. the names of elements and their attributes) are case-insensitive, but only for characters in the ranges U+0041 .. U+005A (LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) and U+0061 .. U+007A (LATIN SMALL LETTER A to LATIN SMALL LETTER Z). For convenience, in this section this is just referred to as "case-insensitive".

8.1.1 The DOCTYPE

A DOCTYPE is a mostly useless, but required, header.

DOCTYPEs are required for legacy reasons. When omitted, browsers tend to use a different rendering mode that is incompatible with some specifications. Including the DOCTYPE in a document ensures that the browser makes a best-effort attempt at following the relevant specifications.

A DOCTYPE must consist of the following characters, in this order:

  1. A U+003C LESS-THAN SIGN (<) character.
  2. A U+0021 EXCLAMATION MARK (!) character.
  3. A string that is an ASCII case-insensitive match for the string "DOCTYPE".
  4. One or more space characters.
  5. A string that is an ASCII case-insensitive match for the string "HTML".
  6. Optionally, a DOCTYPE legacy string (defined below).
  7. Zero or more space characters.
  8. A U+003E GREATER-THAN SIGN (>) character.

In other words, <!DOCTYPE HTML>, case-insensitively.

For the purposes of HTML generators that cannot output HTML markup with the short DOCTYPE "<!DOCTYPE HTML>", a DOCTYPE legacy string may be inserted into the DOCTYPE (in the position defined above). This string must consist of:

  1. One or more space characters.
  2. A string that is an ASCII case-insensitive match for the string "SYSTEM".
  3. One or more space characters.
  4. A U+0022 QUOTATION MARK or U+0027 APOSTROPHE character (the quote mark).
  5. The literal string "about:legacy-compat".
  6. A matching U+0022 QUOTATION MARK or U+0027 APOSTROPHE character (i.e. the same character as in the earlier step marked quote mark).

In other words, <!DOCTYPE HTML SYSTEM "about:legacy-compat"> or <!DOCTYPE HTML SYSTEM 'about:legacy-compat'>, case-insensitively except for the bit in quotes.

The DOCTYPE legacy string should not be used unless the document is generated from a system that cannot output the shorter string.

8.1.2 Elements

There are five different kinds of elements: void elements, CDATA elements, RCDATA elements, foreign elements, and normal elements.

Void elements
area, base, br, col, command, embed, hr, img, input, keygen, link, meta, param, source
CDATA elements
script, style
RCDATA elements
textarea, title
Foreign elements
Elements from the MathML namespace and the SVG namespace.
Normal elements
All other allowed HTML elements are normal elements.

Tags are used to delimit the start and end of elements in the markup. CDATA, RCDATA, and normal elements have a start tag to indicate where they begin, and an end tag to indicate where they end. The start and end tags of certain normal elements can be omitted, as described later. Those that cannot be omitted must not be omitted. Void elements only have a start tag; end tags must not be specified for void elements. Foreign elements must either have a start tag and an end tag, or a start tag that is marked as self-closing, in which case they must not have an end tag.

The contents of the element must be placed between just after the start tag (which might be implied, in certain cases) and just before the end tag (which again, might be implied in certain cases). The exact allowed contents of each individual element depends on the content model of that element, as described earlier in this specification. Elements must not contain content that their content model disallows. In addition to the restrictions placed on the contents by those content models, however, the five types of elements have additional syntactic requirements.

Void elements can't have any contents (since there's no end tag, no content can be put between the start tag and the end tag).

CDATA elements can have text, though it has restrictions described below.

RCDATA elements can have text and character references, but the text must not contain an ambiguous ampersand. There are also further restrictions described below.

Foreign elements whose start tag is marked as self-closing can't have any contents (since, again, as there's no end tag, no content can be put between the start tag and the end tag). Foreign elements whose start tag is not marked as self-closing can have text, character references, CDATA sections, other elements, and comments, but the text must not contain the character U+003C LESS-THAN SIGN (<) or an ambiguous ampersand.

Normal elements can have text, character references, other elements, and comments, but the text must not contain the character U+003C LESS-THAN SIGN (<) or an ambiguous ampersand. Some normal elements also have yet more restrictions on what content they are allowed to hold, beyond the restrictions imposed by the content model and those described in this paragraph. Those restrictions are described below.

Tags contain a tag name, giving the element's name. HTML elements all have names that only use characters in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE, U+0061 LATIN SMALL LETTER A .. U+007A LATIN SMALL LETTER Z, U+0041 LATIN CAPITAL LETTER A .. U+005A LATIN CAPITAL LETTER Z, and U+002D HYPHEN-MINUS (-). In the HTML syntax, tag names may be written with any mix of lower- and uppercase letters that, when converted to all-lowercase, matches the element's tag name; tag names are case-insensitive.

8.1.2.1 Start tags

Start tags must have the following format:

  1. The first character of a start tag must be a U+003C LESS-THAN SIGN (<).
  2. The next few characters of a start tag must be the element's tag name.
  3. If there are to be any attributes in the next step, there must first be one or more space characters.
  4. Then, the start tag may have a number of attributes, the syntax for which is described below. Attributes may be separated from each other by one or more space characters.
  5. After the attributes, there may be one or more space characters. (Some attributes are required to be followed by a space. See the attributes section below.)
  6. Then, if the element is one of the void elements, or if the element is a foreign element, then there may be a single U+002F SOLIDUS (/) character. This character has no effect on void elements, but on foreign elements it marks the start tag as self-closing.
  7. Finally, start tags must be closed by a U+003E GREATER-THAN SIGN (>) character.
8.1.2.2 End tags

End tags must have the following format:

  1. The first character of an end tag must be a U+003C LESS-THAN SIGN (<).
  2. The second character of an end tag must be a U+002F SOLIDUS (/).
  3. The next few characters of an end tag must be the element's tag name.
  4. After the tag name, there may be one or more space characters.
  5. Finally, end tags must be closed by a U+003E GREATER-THAN SIGN (>) character.
8.1.2.3 Attributes

Attributes for an element are expressed inside the element's start tag.

Attributes have a name and a value. Attribute names must consist of one or more characters other than the space characters, U+0000 NULL, U+0022 QUOTATION MARK ("), U+0027 APOSTROPHE ('), U+003E GREATER-THAN SIGN (>), U+002F SOLIDUS (/), and U+003D EQUALS SIGN (=) characters, the control characters, and any characters that are not defined by Unicode. In the HTML syntax, attribute names may be written with any mix of lower- and uppercase letters that are an ASCII case-insensitive match for the attribute's name.

Attribute values are a mixture of text and character references, except with the additional restriction that the text cannot contain an ambiguous ampersand.

Attributes can be specified in four different ways:

Empty attribute syntax

Just the attribute name.

In the following example, the disabled attribute is given with the empty attribute syntax:

<input disabled>

If an attribute using the empty attribute syntax is to be followed by another attribute, then there must be a space character separating the two.

Unquoted attribute value syntax

The attribute name, followed by zero or more space characters, followed by a single U+003D EQUALS SIGN character, followed by zero or more space characters, followed by the attribute value, which, in addition to the requirements given above for attribute values, must not contain any literal space characters, any U+0022 QUOTATION MARK (") characters, U+0027 APOSTROPHE (') characters, U+003D EQUALS SIGN (=) characters, or U+003E GREATER-THAN SIGN (>) characters, and must not be the empty string.

In the following example, the value attribute is given with the unquoted attribute value syntax:

<input value=yes>

If an attribute using the unquoted attribute syntax is to be followed by another attribute or by one of the optional U+002F SOLIDUS (/) characters allowed in step 6 of the start tag syntax above, then there must be a space character separating the two.

Single-quoted attribute value syntax

The attribute name, followed by zero or more space characters, followed by a single U+003D EQUALS SIGN character, followed by zero or more space characters, followed by a single U+0027 APOSTROPHE (') character, followed by the attribute value, which, in addition to the requirements given above for attribute values, must not contain any literal U+0027 APOSTROPHE (') characters, and finally followed by a second single U+0027 APOSTROPHE (') character.

In the following example, the type attribute is given with the single-quoted attribute value syntax:

<input type='checkbox'>

If an attribute using the single-quoted attribute syntax is to be followed by another attribute, then there must be a space character separating the two.

Double-quoted attribute value syntax

The attribute name, followed by zero or more space characters, followed by a single U+003D EQUALS SIGN character, followed by zero or more space characters, followed by a single U+0022 QUOTATION MARK (") character, followed by the attribute value, which, in addition to the requirements given above for attribute values, must not contain any literal U+0022 QUOTATION MARK (") characters, and finally followed by a second single U+0022 QUOTATION MARK (") character.

In the following example, the name attribute is given with the double-quoted attribute value syntax:

<input name="be evil">

If an attribute using the double-quoted attribute syntax is to be followed by another attribute, then there must be a space character separating the two.

There must never be two or more attributes on the same start tag whose names are an ASCII case-insensitive match for each other.

8.1.2.4 Optional tags

Certain tags can be omitted.

Omitting an element's start tag does not mean the element is not present; it is implied, but it is still there. An HTML document always has a root html element, even if the string <html> doesn't appear anywhere in the markup.

An html element's start tag may be omitted if the first thing inside the html element is not a comment.

An html element's end tag may be omitted if the html element is not immediately followed by a comment.

A head element's start tag may be omitted if the first thing inside the head element is an element.

A head element's end tag may be omitted if the head element is not immediately followed by a space character or a comment.

A body element's start tag may be omitted if the element is empty, or if the first thing inside the body element is not a space character or a comment, except if the first thing inside the body element is a script or style element.

A body element's end tag may be omitted if the body element is not immediately followed by a comment.

A li element's end tag may be omitted if the li element is immediately followed by another li element or if there is no more content in the parent element.

A dt element's end tag may be omitted if the dt element is immediately followed by another dt element or a dd element.

A dd element's end tag may be omitted if the dd element is immediately followed by another dd element or a dt element, or if there is no more content in the parent element.

A p element's end tag may be omitted if the p element is immediately followed by an address, article, aside, blockquote, datagrid, dialog, dir, div, dl, fieldset, footer, form, h1, h2, h3, h4, h5, h6, header, hgroup, hr, menu, nav, ol, p, pre, section, table, or ul, element, or if there is no more content in the parent element and the parent element is not an a element.

An rt element's end tag may be omitted if the rt element is immediately followed by an rt or rp element, or if there is no more content in the parent element.

An rp element's end tag may be omitted if the rp element is immediately followed by an rt or rp element, or if there is no more content in the parent element.

An optgroup element's end tag may be omitted if the optgroup element is immediately followed by another optgroup element, or if there is no more content in the parent element.

An option element's end tag may be omitted if the option element is immediately followed by another option element, or if it is immediately followed by an optgroup element, or if there is no more content in the parent element.

A colgroup element's start tag may be omitted if the first thing inside the colgroup element is a col element, and if the element is not immediately preceded by another colgroup element whose end tag has been omitted. (It can't be omitted if the element is empty.)

A colgroup element's end tag may be omitted if the colgroup element is not immediately followed by a space character or a comment.

A thead element's end tag may be omitted if the thead element is immediately followed by a tbody or tfoot element.

A tbody element's start tag may be omitted if the first thing inside the tbody element is a tr element, and if the element is not immediately preceded by a tbody, thead, or tfoot element whose end tag has been omitted. (It can't be omitted if the element is empty.)

A tbody element's end tag may be omitted if the tbody element is immediately followed by a tbody or tfoot element, or if there is no more content in the parent element.

A tfoot element's end tag may be omitted if the tfoot element is immediately followed by a tbody element, or if there is no more content in the parent element.

A tr element's end tag may be omitted if the tr element is immediately followed by another tr element, or if there is no more content in the parent element.

A td element's end tag may be omitted if the td element is immediately followed by a td or th element, or if there is no more content in the parent element.

A th element's end tag may be omitted if the th element is immediately followed by a td or th element, or if there is no more content in the parent element.

However, a start tag must never be omitted if it has any attributes.

8.1.2.5 Restrictions on content models

For historical reasons, certain elements have extra restrictions beyond even the restrictions given by their content model.

A table element must not contain tr elements, even though these elements are technically allowed inside table elements according to the content models described in this specification. (If a tr element is put inside a table in the markup, it will in fact imply a tbody start tag before it.)

A single U+000A LINE FEED (LF) character may be placed immediately after the start tag of pre and textarea elements. This does not affect the processing of the element. The otherwise optional U+000A LINE FEED (LF) character must be included if the element's contents start with that character (because otherwise the leading newline in the contents would be treated like the optional newline, and ignored).

The following two pre blocks are equivalent:

<pre>Hello</pre>
<pre>
Hello</pre>
8.1.2.6 Restrictions on the contents of CDATA and RCDATA elements

The text in CDATA and RCDATA elements must not contain any occurrences of the string "</" (U+003C LESS-THAN SIGN, U+002F SOLIDUS) followed by characters that case-insensitively match the tag name of the element followed by one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), U+0020 SPACE, U+003E GREATER-THAN SIGN (>), or U+002F SOLIDUS (/), unless that string is part of an escaping text span.

An escaping text span is a span of text that starts with an escaping text span start that is not itself in an escaping text span, and ends at the next escaping text span end. There cannot be any character references inside an escaping text span — sequences of characters that would look like character references do not have special meaning.

An escaping text span start is a part of text that consists of the four character sequence "<!--" (U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS).

An escaping text span end is a part of text that consists of the three character sequence "-->" (U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN) whose U+003E GREATER-THAN SIGN (>).

An escaping text span start may share its U+002D HYPHEN-MINUS characters with its corresponding escaping text span end.

The text in CDATA and RCDATA elements must not have an escaping text span start that is not followed by an escaping text span end.

8.1.3 Text

Text is allowed inside elements, attributes, and comments. Text must consist of Unicode characters. Text must not contain U+0000 characters. Text must not contain permanently undefined Unicode characters. Text must not contain control characters other than space characters. Extra constraints are placed on what is and what is not allowed in text based on where the text is to be put, as described in the other sections.

8.1.3.1 Newlines

Newlines in HTML may be represented either as U+000D CARRIAGE RETURN (CR) characters, U+000A LINE FEED (LF) characters, or pairs of U+000D CARRIAGE RETURN (CR), U+000A LINE FEED (LF) characters in that order.

8.1.4 Character references

In certain cases described in other sections, text may be mixed with character references. These can be used to escape characters that couldn't otherwise legally be included in text.

Character references must start with a U+0026 AMPERSAND (&). Following this, there are three possible kinds of character references:

Named character references
The ampersand must be followed by one of the names given in the named character references section, using the same case. The name must be one that is terminated by a U+003B SEMICOLON (;) character.
Decimal numeric character reference
The ampersand must be followed by a U+0023 NUMBER SIGN (#) character, followed by one or more digits in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE, representing a base-ten integer that itself is a Unicode code point that is not U+0000, U+000D, in the range U+0080 .. U+009F, or in the range 0xD800 .. 0xDFFF (surrogates). The digits must then be followed by a U+003B SEMICOLON character (;).
Hexadecimal numeric character reference
The ampersand must be followed by a U+0023 NUMBER SIGN (#) character, which must be followed by either a U+0078 LATIN SMALL LETTER X or a U+0058 LATIN CAPITAL LETTER X character, which must then be followed by one or more digits in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE, U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, and U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, representing a base-sixteen integer that itself is a Unicode code point that is not U+0000, U+000D, in the range U+0080 .. U+009F, or in the range 0xD800 .. 0xDFFF (surrogates). The digits must then be followed by a U+003B SEMICOLON character (;).

An ambiguous ampersand is a U+0026 AMPERSAND (&) character that is followed by some text other than a space character, a U+003C LESS-THAN SIGN character ('<'), or another U+0026 AMPERSAND (&) character.

8.1.5 CDATA sections

CDATA sections must start with the character sequence U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+005B LEFT SQUARE BRACKET, U+0043 LATIN CAPITAL LETTER C, U+0044 LATIN CAPITAL LETTER D, U+0041 LATIN CAPITAL LETTER A, U+0054 LATIN CAPITAL LETTER T, U+0041 LATIN CAPITAL LETTER A, U+005B LEFT SQUARE BRACKET (<![CDATA[). Following this sequence, the CDATA section may have text, with the additional restriction that the text must not contain the three character sequence U+005D RIGHT SQUARE BRACKET, U+005D RIGHT SQUARE BRACKET, U+003E GREATER-THAN SIGN (]]>). Finally, the CDATA section must be ended by the three character sequence U+005D RIGHT SQUARE BRACKET, U+005D RIGHT SQUARE BRACKET, U+003E GREATER-THAN SIGN (]]>).

8.1.6 Comments

Comments must start with the four character sequence U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS (<!--). Following this sequence, the comment may have text, with the additional restriction that the text must not start with a single U+003E GREATER-THAN SIGN ('>') character, nor start with a U+002D HYPHEN-MINUS (-) character followed by a U+003E GREATER-THAN SIGN ('>') character, nor contain two consecutive U+002D HYPHEN-MINUS (-) characters, nor end with a U+002D HYPHEN-MINUS (-) character. Finally, the comment must be ended by the three character sequence U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN (-->).

8.2 Parsing HTML documents

This section only applies to user agents, data mining tools, and conformance checkers.

The rules for parsing XML documents (and thus XHTML documents) into DOM trees are covered by the next section, entitled "The XHTML syntax".

For HTML documents, user agents must use the parsing rules described in this section to generate the DOM trees. Together, these rules define what is referred to as the HTML parser.

While the HTML form of HTML5 bears a close resemblance to SGML and XML, it is a separate language with its own parsing rules.

Some earlier versions of HTML (in particular from HTML2 to HTML4) were based on SGML and used SGML parsing rules. However, few (if any) web browsers ever implemented true SGML parsing for HTML documents; the only user agents to strictly handle HTML as an SGML application have historically been validators. The resulting confusion — with validators claiming documents to have one representation while widely deployed Web browsers interoperably implemented a different representation — has wasted decades of productivity. This version of HTML thus returns to a non-SGML basis.

Authors interested in using SGML tools in their authoring pipeline are encouraged to use XML tools and the XML serialization of HTML5.

This specification defines the parsing rules for HTML documents, whether they are syntactically correct or not. Certain points in the parsing algorithm are said to be parse errors. The error handling for parse errors is well-defined: user agents must either act as described below when encountering such problems, or must abort processing at the first error that they encounter for which they do not wish to apply the rules described below.

Conformance checkers must report at least one parse error condition to the user if one or more parse error conditions exist in the document and must not report parse error conditions if none exist in the document. Conformance checkers may report more than one parse error condition if more than one parse error conditions exist in the document. Conformance checkers are not required to recover from parse errors.

Parse errors are only errors with the syntax of HTML. In addition to checking for parse errors, conformance checkers will also verify that the document obeys all the other conformance requirements described in this specification.

8.2.1 Overview of the parsing model

The input to the HTML parsing process consists of a stream of Unicode characters, which is passed through a tokenization stage followed by a tree construction stage. The output is a Document object.

Implementations that do not support scripting do not have to actually create a DOM Document object, but the DOM tree in such cases is still used as the model for the rest of the specification.

In the common case, the data handled by the tokenization stage comes from the network, but it can also come from script, e.g. using the document.write() API.

There is only one set of states for the tokenizer stage and the tree construction stage, but the tree construction stage is reentrant, meaning that while the tree construction stage is handling one token, the tokenizer might be resumed, causing further tokens to be emitted and processed before the first token's processing is complete.

In the following example, the tree construction stage will be called upon to handle a "p" start tag token while handling the "script" start tag token:

...
<script>
 document.write('<p>');
</script>
...

To handle these cases, parsers have a script nesting level, which must be initially set to zero, and a parser pause flag, which must be initially set to false.

8.2.2 The input stream

The stream of Unicode characters that comprises the input to the tokenization stage will be initially seen by the user agent as a stream of bytes (typically coming over the network or from the local file system). The bytes encode the actual characters according to a particular character encoding, which the user agent must use to decode the bytes into characters.

For XML documents, the algorithm user agents must use to determine the character encoding is given by the XML specification. This section does not apply to XML documents. [XML]

8.2.2.1 Determining the character encoding

In some cases, it might be impractical to unambiguously determine the encoding before parsing the document. Because of this, this specification provides for a two-pass mechanism with an optional pre-scan. Implementations are allowed, as described below, to apply a simplified parsing algorithm to whatever bytes they have available before beginning to parse the document. Then, the real parser is started, using a tentative encoding derived from this pre-parse and other out-of-band metadata. If, while the document is being loaded, the user agent discovers an encoding declaration that conflicts with this information, then the parser can get reinvoked to perform a parse of the document with the real encoding.

User agents must use the following algorithm (the encoding sniffing algorithm) to determine the character encoding to use when decoding a document in the first pass. This algorithm takes as input any out-of-band metadata available to the user agent (e.g. the Content-Type metadata of the document) and all the bytes available so far, and returns an encoding and a confidence. The confidence is either tentative, certain, or irrelevant. The encoding used, and whether the confidence in that encoding is tentative or confident, is used during the parsing to determine whether to change the encoding. If no encoding is necessary, e.g. because the parser is operating on a stream of Unicode characters and doesn't have to use an encoding at all, then the confidence is irrelevant.

  1. If the transport layer specifies an encoding, and it is supported, return that encoding with the confidence certain, and abort these steps.

  2. The user agent may wait for more bytes of the resource to be available, either in this step or at any later step in this algorithm. For instance, a user agent might wait 500ms or 512 bytes, whichever came first. In general preparsing the source to find the encoding improves performance, as it reduces the need to throw away the data structures used when parsing upon finding the encoding information. However, if the user agent delays too long to obtain data to determine the encoding, then the cost of the delay could outweigh any performance improvements from the preparse.

  3. For each of the rows in the following table, starting with the first one and going down, if there are as many or more bytes available than the number of bytes in the first column, and the first bytes of the file match the bytes given in the first column, then return the encoding given in the cell in the second column of that row, with the confidence certain, and abort these steps:

    Bytes in Hexadecimal Encoding
    FE FF UTF-16BE
    FF FE UTF-16LE
    EF BB BF UTF-8

    This step looks for Unicode Byte Order Marks (BOMs).

  4. Otherwise, the user agent will have to search for explicit character encoding information in the file itself. This should proceed as follows:

    Let position be a pointer to a byte in the input stream, initially pointing at the first byte. If at any point during these substeps the user agent either runs out of bytes or decides that scanning further bytes would not be efficient, then skip to the next step of the overall character encoding detection algorithm. User agents may decide that scanning any bytes is not efficient, in which case these substeps are entirely skipped.

    Now, repeat the following "two" steps until the algorithm aborts (either because user agent aborts, as described above, or because a character encoding is found):

    1. If position points to:

      A sequence of bytes starting with: 0x3C 0x21 0x2D 0x2D (ASCII '<!--')

      Advance the position pointer so that it points at the first 0x3E byte which is preceded by two 0x2D bytes (i.e. at the end of an ASCII '-->' sequence) and comes after the 0x3C byte that was found. (The two 0x2D bytes can be the same as the those in the '<!--' sequence.)

      A sequence of bytes starting with: 0x3C, 0x4D or 0x6D, 0x45 or 0x65, 0x54 or 0x74, 0x41 or 0x61, and finally one of 0x09, 0x0A, 0x0C, 0x0D, 0x20, 0x2F (case-insensitive ASCII '<meta' followed by a space or slash)
      1. Advance the position pointer so that it points at the next 0x09, 0x0A, 0x0C, 0x0D, 0x20, or 0x2F byte (the one in sequence of characters matched above).

      2. Get an attribute and its value. If no attribute was sniffed, then skip this inner set of steps, and jump to the second step in the overall "two step" algorithm.

      3. If the attribute's name is neither "charset" nor "content", then return to step 2 in these inner steps.

      4. If the attribute's name is "charset", let charset be the attribute's value, interpreted as a character encoding.

      5. Otherwise, the attribute's name is "content": apply the algorithm for extracting an encoding from a Content-Type, giving the attribute's value as the string to parse. If an encoding is returned, let charset be that encoding. Otherwise, return to step 2 in these inner steps.

      6. If charset is a UTF-16 encoding, change it to UTF-8.

      7. If charset is a supported character encoding, then return the given encoding, with confidence tentative, and abort all these steps.

      8. Otherwise, return to step 2 in these inner steps.

      A sequence of bytes starting with a 0x3C byte (ASCII '<'), optionally a 0x2F byte (ASCII '/'), and finally a byte in the range 0x41-0x5A or 0x61-0x7A (an ASCII letter)
      1. Advance the position pointer so that it points at the next 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0C (ASCII FF), 0x0D (ASCII CR), 0x20 (ASCII space), or 0x3E (ASCII '>') byte.

      2. Repeatedly get an attribute until no further attributes can be found, then jump to the second step in the overall "two step" algorithm.

      A sequence of bytes starting with: 0x3C 0x21 (ASCII '<!')
      A sequence of bytes starting with: 0x3C 0x2F (ASCII '</')
      A sequence of bytes starting with: 0x3C 0x3F (ASCII '<?')

      Advance the position pointer so that it points at the first 0x3E byte (ASCII '>') that comes after the 0x3C byte that was found.

      Any other byte

      Do nothing with that byte.

    2. Move position so it points at the next byte in the input stream, and return to the first step of this "two step" algorithm.

    When the above "two step" algorithm says to get an attribute, it means doing this:

    1. If the byte at position is one of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0C (ASCII FF), 0x0D (ASCII CR), 0x20 (ASCII space), or 0x2F (ASCII '/') then advance position to the next byte and redo this substep.

    2. If the byte at position is 0x3E (ASCII '>'), then abort the "get an attribute" algorithm. There isn't one.

    3. Otherwise, the byte at position is the start of the attribute name. Let attribute name and attribute value be the empty string.

    4. Attribute name: Process the byte at position as follows:

      If it is 0x3D (ASCII '='), and the attribute name is longer than the empty string
      Advance position to the next byte and jump to the step below labeled value.
      If it is 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0C (ASCII FF), 0x0D (ASCII CR), or 0x20 (ASCII space)
      Jump to the step below labeled spaces.
      If it is 0x2F (ASCII '/') or 0x3E (ASCII '>')
      Abort the "get an attribute" algorithm. The attribute's name is the value of attribute name, its value is the empty string.
      If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')
      Append the Unicode character with code point b+0x20 to attribute name (where b is the value of the byte at position).
      Anything else
      Append the Unicode character with the same code point as the value of the byte at position) to attribute name. (It doesn't actually matter how bytes outside the ASCII range are handled here, since only ASCII characters can contribute to the detection of a character encoding.)
    5. Advance position to the next byte and return to the previous step.

    6. Spaces. If the byte at position is one of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0C (ASCII FF), 0x0D (ASCII CR), or 0x20 (ASCII space) then advance position to the next byte, then, repeat this step.

    7. If the byte at position is not 0x3D (ASCII '='), abort the "get an attribute" algorithm. The attribute's name is the value of attribute name, its value is the empty string.

    8. Advance position past the 0x3D (ASCII '=') byte.

    9. Value. If the byte at position is one of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0C (ASCII FF), 0x0D (ASCII CR), or 0x20 (ASCII space) then advance position to the next byte, then, repeat this step.

    10. Process the byte at position as follows:

      If it is 0x22 (ASCII '"') or 0x27 ("'")
      1. Let b be the value of the byte at position.
      2. Advance position to the next byte.
      3. If the value of the byte at position is the value of b, then advance position to the next byte and abort the "get an attribute" algorithm. The attribute's name is the value of attribute name, and its value is the value of attribute value.
      4. Otherwise, if the value of the byte at position is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z'), then append a Unicode character to attribute value whose code point is 0x20 more than the value of the byte at position.
      5. Otherwise, append a Unicode character to attribute value whose code point is the same as the value of the byte at position.
      6. Return to the second step in these substeps.
      If it is 0x3E (ASCII '>')
      Abort the "get an attribute" algorithm. The attribute's name is the value of attribute name, its value is the empty string.
      If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')
      Append the Unicode character with code point b+0x20 to attribute value (where b is the value of the byte at position). Advance position to the next byte.
      Anything else
      Append the Unicode character with the same code point as the value of the byte at position) to attribute value. Advance position to the next byte.
    11. Process the byte at position as follows:

      If it is 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0C (ASCII FF), 0x0D (ASCII CR), 0x20 (ASCII space), or 0x3E (ASCII '>')
      Abort the "get an attribute" algorithm. The attribute's name is the value of attribute name and its value is the value of attribute value.
      If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')
      Append the Unicode character with code point b+0x20 to attribute value (where b is the value of the byte at position).
      Anything else
      Append the Unicode character with the same code point as the value of the byte at position) to attribute value.
    12. Advance position to the next byte and return to the previous step.

    For the sake of interoperability, user agents should not use a pre-scan algorithm that returns different results than the one described above. (But, if you do, please at least let us know, so that we can improve this algorithm and benefit everyone...)

  5. If the user agent has information on the likely encoding for this page, e.g. based on the encoding of the page when it was last visited, then return that encoding, with the confidence tentative, and abort these steps.

  6. The user agent may attempt to autodetect the character encoding from applying frequency analysis or other algorithms to the data stream. If autodetection succeeds in determining a character encoding, then return that encoding, with the confidence tentative, and abort these steps. [UNIVCHARDET]

  7. Otherwise, return an implementation-defined or user-specified default character encoding, with the confidence tentative. In non-legacy environments, the more comprehensive UTF-8 encoding is recommended. Due to its use in legacy content, windows-1252 is recommended as a default in predominantly Western demographics instead. Since these encodings can in many cases be distinguished by inspection, a user agent may heuristically decide which to use as a default.

The document's character encoding must immediately be set to the value returned from this algorithm, at the same time as the user agent uses the returned value to select the decoder to use for the input stream.

8.2.2.2 Preprocessing the input stream

Given an encoding, the bytes in the input stream must be converted to Unicode characters for the tokenizer, as described by the rules for that encoding, except that the leading U+FEFF BYTE ORDER MARK character, if any, must not be stripped by the encoding layer (it is stripped by the rule below).

Bytes or sequences of bytes in the original byte stream that could not be converted to Unicode characters must be converted to U+FFFD REPLACEMENT CHARACTER code points.

Bytes or sequences of bytes in the original byte stream that did not conform to the encoding specification (e.g. invalid UTF-8 byte sequences in a UTF-8 input stream) are errors that conformance checkers are expected to report.

Any byte or sequences of bytes in the original byte stream that is misinterpreted for compatibility is a parse error.

One leading U+FEFF BYTE ORDER MARK character must be ignored if any are present.

All U+0000 NULL characters in the input must be replaced by U+FFFD REPLACEMENT CHARACTERs. Any occurrences of such characters is a parse error.

Any occurrences of any characters in the ranges U+0001 to U+0008, U+000E to U+001F, U+007F to U+009F, U+D800 to U+DFFF, U+FDD0 to U+FDEF, and characters U+000B, U+FFFE, U+FFFF, U+1FFFE, U+1FFFF, U+2FFFE, U+2FFFF, U+3FFFE, U+3FFFF, U+4FFFE, U+4FFFF, U+5FFFE, U+5FFFF, U+6FFFE, U+6FFFF, U+7FFFE, U+7FFFF, U+8FFFE, U+8FFFF, U+9FFFE, U+9FFFF, U+AFFFE, U+AFFFF, U+BFFFE, U+BFFFF, U+CFFFE, U+CFFFF, U+DFFFE, U+DFFFF, U+EFFFE, U+EFFFF, U+FFFFE, U+FFFFF, U+10FFFE, and U+10FFFF are parse errors. (These are all control characters or permanently undefined Unicode characters.)

U+000D CARRIAGE RETURN (CR) characters and U+000A LINE FEED (LF) characters are treated specially. Any CR characters that are followed by LF characters must be removed, and any CR characters not followed by LF characters must be converted to LF characters. Thus, newlines in HTML DOMs are represented by LF characters, and there are never any CR characters in the input to the tokenization stage.

The next input character is the first character in the input stream that has not yet been consumed. Initially, the next input character is the first character in the input. The current input character is the last character to have been consumed.

The insertion point is the position (just before a character or just before the end of the input stream) where content inserted using document.write() is actually inserted. The insertion point is relative to the position of the character immediately after it, it is not an absolute offset into the input stream. Initially, the insertion point is uninitialized.

The "EOF" character in the tables below is a conceptual character representing the end of the input stream. If the parser is a script-created parser, then the end of the input stream is reached when an explicit "EOF" character (inserted by the document.close() method) is consumed. Otherwise, the "EOF" character is not a real character in the stream, but rather the lack of any further characters.

8.2.2.3 Changing the encoding while parsing

When the parser requires the user agent to change the encoding, it must run the following steps. This might happen if the encoding sniffing algorithm described above failed to find an encoding, or if it found an encoding that was not the actual encoding of the file.

  1. If the new encoding is a UTF-16 encoding, change it to UTF-8.
  2. If the new encoding is identical or equivalent to the encoding that is already being used to interpret the input stream, then set the confidence to confident and abort these steps. This happens when the encoding information found in the file matches what the encoding sniffing algorithm determined to be the encoding, and in the second pass through the parser if the first pass found that the encoding sniffing algorithm described in the earlier section failed to find the right encoding.
  3. If all the bytes up to the last byte converted by the current decoder have the same Unicode interpretations in both the current encoding and the new encoding, and if the user agent supports changing the converter on the fly, then the user agent may change to the new converter for the encoding on the fly. Set the document's character encoding and the encoding used to convert the input stream to the new encoding, set the confidence to confident, and abort these steps.
  4. Otherwise, navigate to the document again, with replacement enabled, and using the same source browsing context, but this time skip the encoding sniffing algorithm and instead just set the encoding to the new encoding and the confidence to confident. Whenever possible, this should be done without actually contacting the network layer (the bytes should be re-parsed from memory), even if, e.g., the document is marked as not being cacheable. If this is not possible and contacting the network layer would involve repeating a request that uses a method other than HTTP GET (or equivalent for non-HTTP URLs), then instead set the confidence to confident and ignore the new encoding. The resource will be misinterpreted. User agents may notify the user of the situation, to aid in application development.

8.2.3 Parse state

8.2.3.1 The insertion mode

The insertion mode is a state variable that controls the primary operation of the tree construction stage.

Initially, the insertion mode is "initial". It can change to "before html", "before head", "in head", "in head noscript", "after head", "in body", "in CDATA/RCDATA", "in table", "in caption", "in column group", "in table body", "in row", "in cell", "in select", "in select in table", "in foreign content", "after body", "in frameset", "after frameset", "after after body", and "after after frameset" during the course of the parsing, as described in the tree construction stage. The insertion mode affects how tokens are processed and whether CDATA sections are supported.

Seven of these modes, namely "in head", "in body", "in CDATA/RCDATA", "in table", "in table body", "in row", "in cell", and "in select", are special, in that the other modes defer to them at various times. When the algorithm below says that the user agent is to do something "using the rules for the m insertion mode", where m is one of these modes, the user agent must use the rules described under the m insertion mode's section, but must leave the insertion mode unchanged unless the rules in m themselves switch the insertion mode to a new value.

When the insertion mode is switched to "in CDATA/RCDATA", the original insertion mode is also set. This is the insertion mode to which the tree construction stage will return when the corresponding end tag is parsed.

When the insertion mode is switched to "in foreign content", the secondary insertion mode is also set. This secondary mode is used within the rules for the "in foreign content" mode to handle HTML (i.e. not foreign) content.


When the steps below require the UA to reset the insertion mode appropriately, it means the UA must follow these steps:

  1. Let last be false.
  2. Let node be the last node in the stack of open elements.
  3. If node is the first node in the stack of open elements, then set last to true and set node to the context element. (fragment case)
  4. If node is a select element, then switch the insertion mode to "in select" and abort these steps. (fragment case)
  5. If node is a td or th element and last is false, then switch the insertion mode to "in cell" and abort these steps.
  6. If node is a tr element, then switch the insertion mode to "in row" and abort these steps.
  7. If node is a tbody, thead, or tfoot element, then switch the insertion mode to "in table body" and abort these steps.
  8. If node is a caption element, then switch the insertion mode to "in caption" and abort these steps.
  9. If node is a colgroup element, then switch the insertion mode to "in column group" and abort these steps. (fragment case)
  10. If node is a table element, then switch the insertion mode to "in table" and abort these steps.
  11. If node is an element from the MathML namespace or the SVG namespace, then switch the insertion mode to "in foreign content", let the secondary insertion mode be "in body", and abort these steps.
  12. If node is a head element, then switch the insertion mode to "in body" ("in body"! not "in head"!) and abort these steps. (fragment case)
  13. If node is a body element, then switch the insertion mode to "in body" and abort these steps.
  14. If node is a frameset element, then switch the insertion mode to "in frameset" and abort these steps. (fragment case)
  15. If node is an html element, then: if the head element pointer is null, switch the insertion mode to "before head", otherwise, switch the insertion mode to "after head". In either case, abort these steps. (fragment case)
  16. If last is true, then switch the insertion mode to "in body" and abort these steps. (fragment case)
  17. Let node now be the node before node in the stack of open elements.
  18. Return to step 3.
8.2.3.2 The stack of open elements

Initially, the stack of open elements is empty. The stack grows downwards; the topmost node on the stack is the first one added to the stack, and the bottommost node of the stack is the most recently added node in the stack (notwithstanding when the stack is manipulated in a random access fashion as part of the handling for misnested tags).

The "before html" insertion mode creates the html root element node, which is then added to the stack.

In the fragment case, the stack of open elements is initialized to contain an html element that is created as part of that algorithm. (The fragment case skips the "before html" insertion mode.)

The html node, however it is created, is the topmost node of the stack. It never gets popped off the stack.

The current node is the bottommost node in this stack.

The current table is the last table element in the stack of open elements, if there is one. If there is no table element in the stack of open elements (fragment case), then the current table is the first element in the stack of open elements (the html element).

Elements in the stack fall into the following categories:

Special

The following HTML elements have varying levels of special parsing rules: address, area, article, aside, base, basefont, bgsound, blockquote, body, br, center, col, colgroup, command, datagrid, dd, details, dialog, dir, div, dl, dt, embed, fieldset, figure, footer, form, frame, frameset, h1, h2, h3, h4, h5, h6, head, header, hgroup, hr, iframe, img, input, isindex, li, link, listing, menu, meta, nav, noembed, noframes, noscript, ol, p, param, plaintext, pre, script, section, select, spacer, style, tbody, textarea, tfoot, thead, title, tr, ul, and wbr.

Scoping

The following HTML elements introduce new scopes for various parts of the parsing: applet, button, caption, html, marquee, object, table, td, th, and SVG's foreignObject.

Formatting

The following HTML elements are those that end up in the list of active formatting elements: a, b, big, code, em, font, i, nobr, s, small, strike, strong, tt, and u.

Phrasing

All other elements found while parsing an HTML document.

The stack of open elements is said to have an element in scope when the following algorithm terminates in a match state:

  1. Initialize node to be the current node (the bottommost node of the stack).

  2. If node is the target node, terminate in a match state.

  3. Otherwise, if node is one of the following elements, terminate in a failure state:

    • applet in the HTML namespace
    • caption in the HTML namespace
    • html in the HTML namespace
    • table in the HTML namespace
    • td in the HTML namespace
    • th in the HTML namespace
    • button in the HTML namespace
    • marquee in the HTML namespace
    • object in the HTML namespace
    • foreignObject in the SVG namespace
  4. Otherwise, set node to the previous entry in the stack of open elements and return to step 2. (This will never fail, since the loop will always terminate in the previous step if the top of the stack — an html element — is reached.)

The stack of open elements is said to have an element in table scope when the following algorithm terminates in a match state:

  1. Initialize node to be the current node (the bottommost node of the stack).

  2. If node is the target node, terminate in a match state.

  3. Otherwise, if node is one of the following elements, terminate in a failure state:

    • html in the HTML namespace
    • table in the HTML namespace
  4. Otherwise, set node to the previous entry in the stack of open elements and return to step 2. (This will never fail, since the loop will always terminate in the previous step if the top of the stack — an html element — is reached.)

Nothing happens if at any time any of the elements in the stack of open elements are moved to a new location in, or removed from, the Document tree. In particular, the stack is not changed in this situation. This can cause, amongst other strange effects, content to be appended to nodes that are no longer in the DOM.

In some cases (namely, when closing misnested formatting elements), the stack is manipulated in a random-access fashion.

8.2.3.3 The list of active formatting elements

Initially, the list of active formatting elements is empty. It is used to handle mis-nested formatting element tags.

The list contains elements in the formatting category, and scope markers. The scope markers are inserted when entering applet elements, buttons, object elements, marquees, table cells, and table captions, and are used to prevent formatting from "leaking" into applet elements, buttons, object elements, marquees, and tables.

In addition, each element in the list of active formatting elements is associated with the token for which it was created, so that further elements can be created for that token if necessary.

When the steps below require the UA to reconstruct the active formatting elements, the UA must perform the following steps:

  1. If there are no entries in the list of active formatting elements, then there is nothing to reconstruct; stop this algorithm.
  2. If the last (most recently added) entry in the list of active formatting elements is a marker, or if it is an element that is in the stack of open elements, then there is nothing to reconstruct; stop this algorithm.
  3. Let entry be the last (most recently added) element in the list of active formatting elements.
  4. If there are no entries before entry in the list of active formatting elements, then jump to step 8.
  5. Let entry be the entry one earlier than entry in the list of active formatting elements.
  6. If entry is neither a marker nor an element that is also in the stack of open elements, go to step 4.
  7. Let entry be the element one later than entry in the list of active formatting elements.
  8. Create an element for the token for which the element entry was created, to obtain new element.
  9. Append new element to the current node and push it onto the stack of open elements so that it is the new current node.
  10. Replace the entry for entry in the list with an entry for new element.
  11. If the entry for new element in the list of active formatting elements is not the last entry in the list, return to step 7.

This has the effect of reopening all the formatting elements that were opened in the current body, cell, or caption (whichever is youngest) that haven't been explicitly closed.

The way this specification is written, the list of active formatting elements always consists of elements in chronological order with the least recently added element first and the most recently added element last (except for while steps 8 to 11 of the above algorithm are being executed, of course).

When the steps below require the UA to clear the list of active formatting elements up to the last marker, the UA must perform the following steps:

  1. Let entry be the last (most recently added) entry in the list of active formatting elements.
  2. Remove entry from the list of active formatting elements.
  3. If entry was a marker, then stop the algorithm at this point. The list has been cleared up to the last marker.
  4. Go to step 1.
8.2.3.4 The element pointers

Initially, the head element pointer and the form element pointer are both null.

Once a head element has been parsed (whether implicitly or explicitly) the head element pointer gets set to point to this node.

The form element pointer points to the last form element that was opened and whose end tag has not yet been seen. It is used to make form controls associate with forms in the face of dramatically bad markup, for historical reasons.

8.2.3.5 Other parsing state flags

The scripting flag is set to "enabled" if scripting was enabled for the Document with which the parser is associated when the parser was created, and "disabled" otherwise.

The frameset-ok flag is set to "ok" when the parser is created. It is set to "not ok" after certain tokens are seen.

8.2.4 Tokenization

Implementations must act as if they used the following state machine to tokenize HTML. The state machine must start in the data state. Most states consume a single character, which may have various side-effects, and either switches the state machine to a new state to reconsume the same character, or switches it to a new state (to consume the next character), or repeats the same state (to consume the next character). Some states have more complicated behavior and can consume several characters before switching to another state.

The exact behavior of certain states depends on a content model flag that is set after certain tokens are emitted. The flag has several states: PCDATA, RCDATA, CDATA, and PLAINTEXT. Initially, it must be in the PCDATA state. In the RCDATA and CDATA states, a further escape flag is used to control the behavior of the tokenizer. It is either true or false, and initially must be set to the false state. The insertion mode and the stack of open elements also affects tokenization.

The output of the tokenization step is a series of zero or more of the following tokens: DOCTYPE, start tag, end tag, comment, character, end-of-file. DOCTYPE tokens have a name, a public identifier, a system identifier, and a force-quirks flag. When a DOCTYPE token is created, its name, public identifier, and system identifier must be marked as missing (which is a distinct state from the empty string), and the force-quirks flag must be set to off (its other state is on). Start and end tag tokens have a tag name, a self-closing flag, and a list of attributes, each of which has a name and a value. When a start or end tag token is created, its self-closing flag must be unset (its other state is that it be set), and its attributes list must be empty. Comment and character tokens have data.

When a token is emitted, it must immediately be handled by the tree construction stage. The tree construction stage can affect the state of the content model flag, and can insert additional characters into the stream. (For example, the script element can result in scripts executing and using the dynamic markup insertion APIs to insert characters into the stream being tokenized.)

When a start tag token is emitted with its self-closing flag set, if the flag is not acknowledged when it is processed by the tree construction stage, that is a parse error.

When an end tag token is emitted, the content model flag must be switched to the PCDATA state.

When an end tag token is emitted with attributes, that is a parse error.

When an end tag token is emitted with its self-closing flag set, that is a parse error.

Before each step of the tokenizer, the user agent must first check the parser pause flag. If it is true, then the tokenizer must abort the processing of any nested invocations of the tokenizer, yielding control back to the caller. If it is false, then the user agent may then check to see if either one of the scripts in the list of scripts that will execute as soon as possible or the first script in the list of scripts that will execute asynchronously, has completed loading. If one has, then it must be executed and removed from its list.

The tokenizer state machine consists of the states defined in the following subsections.

8.2.4.1 Data state

Consume the next input character:

U+0026 AMPERSAND (&)
When the content model flag is set to one of the PCDATA or RCDATA states and the escape flag is false: switch to the character reference data state.
Otherwise: treat it as per the "anything else" entry below.
U+002D HYPHEN-MINUS (-)

If the content model flag is set to either the RCDATA state or the CDATA state, and the escape flag is false, and there are at least three characters before this one in the input stream, and the last four characters in the input stream, including this one, are U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, and U+002D HYPHEN-MINUS ("<!--"), then set the escape flag to true.

In any case, emit the input character as a character token. Stay in the data state.

U+003C LESS-THAN SIGN (<)
When the content model flag is set to the PCDATA state: switch to the tag open state.
When the content model flag is set to either the RCDATA state or the CDATA state, and the escape flag is false: switch to the tag open state.
Otherwise: treat it as per the "anything else" entry below.
U+003E GREATER-THAN SIGN (>)

If the content model flag is set to either the RCDATA state or the CDATA state, and the escape flag is true, and the last three characters in the input stream including this one are U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN ("-->"), set the escape flag to false.

In any case, emit the input character as a character token. Stay in the data state.

EOF
Emit an end-of-file token.
Anything else
Emit the input character as a character token. Stay in the data state.
8.2.4.2 Character reference data state

(This cannot happen if the content model flag is set to the CDATA state.)

Attempt to consume a character reference, with no additional allowed character.

If nothing is returned, emit a U+0026 AMPERSAND character token.

Otherwise, emit the character token that was returned.

Finally, switch to the data state.

8.2.4.3 Tag open state

The behavior of this state depends on the content model flag.

If the content model flag is set to the RCDATA or CDATA states

Consume the next input character. If it is a U+002F SOLIDUS (/) character, switch to the close tag open state. Otherwise, emit a U+003C LESS-THAN SIGN character token and reconsume the current input character in the data state.

If the content model flag is set to the PCDATA state

Consume the next input character:

U+0021 EXCLAMATION MARK (!)
Switch to the markup declaration open state.
U+002F SOLIDUS (/)
Switch to the close tag open state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Create a new start tag token, set its tag name to the lowercase version of the input character (add 0x0020 to the character's code point), then switch to the tag name state. (Don't emit the token yet; further details will be filled in before it is emitted.)
U+0061 LATIN SMALL LETTER A through to U+007A LATIN SMALL LETTER Z
Create a new start tag token, set its tag name to the input character, then switch to the tag name state. (Don't emit the token yet; further details will be filled in before it is emitted.)
U+003E GREATER-THAN SIGN (>)
Parse error. Emit a U+003C LESS-THAN SIGN character token and a U+003E GREATER-THAN SIGN character token. Switch to the data state.
U+003F QUESTION MARK (?)
Parse error. Switch to the bogus comment state.
Anything else
Parse error. Emit a U+003C LESS-THAN SIGN character token and reconsume the current input character in the data state.
8.2.4.4 Close tag open state

If the content model flag is set to the RCDATA or CDATA states but no start tag token has ever been emitted by this instance of the tokenizer (fragment case), or, if the content model flag is set to the RCDATA or CDATA states and the next few characters do not match the tag name of the last start tag token emitted (compared in an ASCII case-insensitive manner), or if they do but they are not immediately followed by one of the following characters:

...then emit a U+003C LESS-THAN SIGN character token, a U+002F SOLIDUS character token, and switch to the data state to process the next input character.

Otherwise, if the content model flag is set to the PCDATA state, or if the next few characters do match that tag name, consume the next input character:

U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Create a new end tag token, set its tag name to the lowercase version of the input character (add 0x0020 to the character's code point), then switch to the tag name state. (Don't emit the token yet; further details will be filled in before it is emitted.)
U+0061 LATIN SMALL LETTER A through to U+007A LATIN SMALL LETTER Z
Create a new end tag token, set its tag name to the input character, then switch to the tag name state. (Don't emit the token yet; further details will be filled in before it is emitted.)
U+003E GREATER-THAN SIGN (>)
Parse error. Switch to the data state.
EOF
Parse error. Emit a U+003C LESS-THAN SIGN character token and a U+002F SOLIDUS character token. Reconsume the EOF character in the data state.
Anything else
Parse error. Switch to the bogus comment state.
8.2.4.5 Tag name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the before attribute name state.
U+002F SOLIDUS (/)
Switch to the self-closing start tag state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Append the lowercase version of the current input character (add 0x0020 to the character's code point) to the current tag token's tag name. Stay in the tag name state.
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current tag token's tag name. Stay in the tag name state.
8.2.4.6 Before attribute name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before attribute name state.
U+002F SOLIDUS (/)
Switch to the self-closing start tag state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Start a new attribute in the current tag token. Set that attribute's name to the lowercase version of the current input character (add 0x0020 to the character's code point), and its value to the empty string. Switch to the attribute name state.
U+0022 QUOTATION MARK (")
U+0027 APOSTROPHE (')
U+003D EQUALS SIGN (=)
Parse error. Treat it as per the "anything else" entry below.
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Start a new attribute in the current tag token. Set that attribute's name to the current input character, and its value to the empty string. Switch to the attribute name state.
8.2.4.7 Attribute name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the after attribute name state.
U+002F SOLIDUS (/)
Switch to the self-closing start tag state.
U+003D EQUALS SIGN (=)
Switch to the before attribute value state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Append the lowercase version of the current input character (add 0x0020 to the character's code point) to the current attribute's name. Stay in the attribute name state.
U+0022 QUOTATION MARK (")
U+0027 APOSTROPHE (')
Parse error. Treat it as per the "anything else" entry below.
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current attribute's name. Stay in the attribute name state.

When the user agent leaves the attribute name state (and before emitting the tag token, if appropriate), the complete attribute's name must be compared to the other attributes on the same token; if there is already an attribute on the token with the exact same name, then this is a parse error and the new attribute must be dropped, along with the value that gets associated with it (if any).

8.2.4.8 After attribute name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the after attribute name state.
U+002F SOLIDUS (/)
Switch to the self-closing start tag state.
U+003D EQUALS SIGN (=)
Switch to the before attribute value state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Start a new attribute in the current tag token. Set that attribute's name to the lowercase version of the current input character (add 0x0020 to the character's code point), and its value to the empty string. Switch to the attribute name state.
U+0022 QUOTATION MARK (")
U+0027 APOSTROPHE (')
Parse error. Treat it as per the "anything else" entry below.
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Start a new attribute in the current tag token. Set that attribute's name to the current input character, and its value to the empty string. Switch to the attribute name state.
8.2.4.9 Before attribute value state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before attribute value state.
U+0022 QUOTATION MARK (")
Switch to the attribute value (double-quoted) state.
U+0026 AMPERSAND (&)
Switch to the attribute value (unquoted) state and reconsume this input character.
U+0027 APOSTROPHE (')
Switch to the attribute value (single-quoted) state.
U+003E GREATER-THAN SIGN (>)
Parse error. Emit the current tag token. Switch to the data state.
U+003D EQUALS SIGN (=)
Parse error. Treat it as per the "anything else" entry below.
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current attribute's value. Switch to the attribute value (unquoted) state.
8.2.4.10 Attribute value (double-quoted) state

Consume the next input character:

U+0022 QUOTATION MARK (")
Switch to the after attribute value (quoted) state.
U+0026 AMPERSAND (&)
Switch to the character reference in attribute value state, with the additional allowed character being U+0022 QUOTATION MARK (").
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current attribute's value. Stay in the attribute value (double-quoted) state.
8.2.4.11 Attribute value (single-quoted) state

Consume the next input character:

U+0027 APOSTROPHE (')
Switch to the after attribute value (quoted) state.
U+0026 AMPERSAND (&)
Switch to the character reference in attribute value state, with the additional allowed character being U+0027 APOSTROPHE (').
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current attribute's value. Stay in the attribute value (single-quoted) state.
8.2.4.12 Attribute value (unquoted) state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the before attribute name state.
U+0026 AMPERSAND (&)
Switch to the character reference in attribute value state, with no additional allowed character.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0022 QUOTATION MARK (")
U+0027 APOSTROPHE (')
U+003D EQUALS SIGN (=)
Parse error. Treat it as per the "anything else" entry below.
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current attribute's value. Stay in the attribute value (unquoted) state.
8.2.4.13 Character reference in attribute value state

Attempt to consume a character reference.

If nothing is returned, append a U+0026 AMPERSAND character to the current attribute's value.

Otherwise, append the returned character token to the current attribute's value.

Finally, switch back to the attribute value state that you were in when were switched into this state.

8.2.4.14 After attribute value (quoted) state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the before attribute name state.
U+002F SOLIDUS (/)
Switch to the self-closing start tag state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Parse error. Reconsume the character in the before attribute name state.
8.2.4.15 Self-closing start tag state

Consume the next input character:

U+003E GREATER-THAN SIGN (>)
Set the self-closing flag of the current tag token. Emit the current tag token. Switch to the data state.
EOF
Parse error. Reconsume the EOF character in the data state.
Anything else
Parse error. Reconsume the character in the before attribute name state.
8.2.4.16 Bogus comment state

(This can only happen if the content model flag is set to the PCDATA state.)

Consume every character up to and including the first U+003E GREATER-THAN SIGN character (>) or the end of the file (EOF), whichever comes first. Emit a comment token whose data is the concatenation of all the characters starting from and including the character that caused the state machine to switch into the bogus comment state, up to and including the character immediately before the last consumed character (i.e. up to the character just before the U+003E or EOF character). (If the comment was started by the end of the file (EOF), the token is empty.)

Switch to the data state.

If the end of the file was reached, reconsume the EOF character.

8.2.4.17 Markup declaration open state

(This can only happen if the content model flag is set to the PCDATA state.)

If the next two characters are both U+002D HYPHEN-MINUS (-) characters, consume those two characters, create a comment token whose data is the empty string, and switch to the comment start state.

Otherwise, if the next seven characters are an ASCII case-insensitive match for the word "DOCTYPE", then consume those characters and switch to the DOCTYPE state.

Otherwise, if the insertion mode is "in foreign content" and the current node is not an element in the HTML namespace and the next seven characters are an ASCII case-sensitive match for the string "[CDATA[" (the five uppercase letters "CDATA" with a U+005B LEFT SQUARE BRACKET character before and after), then consume those characters and switch to the CDATA section state (which is unrelated to the content model flag's CDATA state).

Otherwise, this is a parse error. Switch to the bogus comment state. The next character that is consumed, if any, is the first character that will be in the comment.

8.2.4.18 Comment start state

Consume the next input character:

U+002D HYPHEN-MINUS (-)
Switch to the comment start dash state.
U+003E GREATER-THAN SIGN (>)
Parse error. Emit the comment token. Switch to the data state.
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Append the input character to the comment token's data. Switch to the comment state.
8.2.4.19 Comment start dash state

Consume the next input character:

U+002D HYPHEN-MINUS (-)
Switch to the comment end state
U+003E GREATER-THAN SIGN (>)
Parse error. Emit the comment token. Switch to the data state.
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Append a U+002D HYPHEN-MINUS (-) character and the input character to the comment token's data. Switch to the comment state.
8.2.4.20 Comment state

Consume the next input character:

U+002D HYPHEN-MINUS (-)
Switch to the comment end dash state
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Append the input character to the comment token's data. Stay in the comment state.
8.2.4.21 Comment end dash state

Consume the next input character:

U+002D HYPHEN-MINUS (-)
Switch to the comment end state
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Append a U+002D HYPHEN-MINUS (-) character and the input character to the comment token's data. Switch to the comment state.
8.2.4.22 Comment end state

Consume the next input character:

U+003E GREATER-THAN SIGN (>)
Emit the comment token. Switch to the data state.
U+002D HYPHEN-MINUS (-)
Parse error. Append a U+002D HYPHEN-MINUS (-) character to the comment token's data. Stay in the comment end state.
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Parse error. Append two U+002D HYPHEN-MINUS (-) characters and the input character to the comment token's data. Switch to the comment state.
8.2.4.23 DOCTYPE state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the before DOCTYPE name state.
Anything else
Parse error. Reconsume the current character in the before DOCTYPE name state.
8.2.4.24 Before DOCTYPE name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before DOCTYPE name state.
U+003E GREATER-THAN SIGN (>)
Parse error. Create a new DOCTYPE token. Set its force-quirks flag to on. Emit the token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Create a new DOCTYPE token. Set the token's name to the lowercase version of the input character (add 0x0020 to the character's code point). Switch to the DOCTYPE name state.
EOF
Parse error. Create a new DOCTYPE token. Set its force-quirks flag to on. Emit the token. Reconsume the EOF character in the data state.
Anything else
Create a new DOCTYPE token. Set the token's name to the current input character. Switch to the DOCTYPE name state.
8.2.4.25 DOCTYPE name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the after DOCTYPE name state.
U+003E GREATER-THAN SIGN (>)
Emit the current DOCTYPE token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Append the lowercase version of the input character (add 0x0020 to the character's code point) to the current DOCTYPE token's name. Stay in the DOCTYPE name state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's name. Stay in the DOCTYPE name state.
8.2.4.26 After DOCTYPE name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the after DOCTYPE name state.
U+003E GREATER-THAN SIGN (>)
Emit the current DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else

If the six characters starting from the current input character are an ASCII case-insensitive match for the word "PUBLIC", then consume those characters and switch to the before DOCTYPE public identifier state.

Otherwise, if the six characters starting from the current input character are an ASCII case-insensitive match for the word "SYSTEM", then consume those characters and switch to the before DOCTYPE system identifier state.

Otherwise, this is the parse error. Set the DOCTYPE token's force-quirks flag to on. Switch to the bogus DOCTYPE state.

8.2.4.27 Before DOCTYPE public identifier state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before DOCTYPE public identifier state.
U+0022 QUOTATION MARK (")
Set the DOCTYPE token's public identifier to the empty string (not missing), then switch to the DOCTYPE public identifier (double-quoted) state.
U+0027 APOSTROPHE (')
Set the DOCTYPE token's public identifier to the empty string (not missing), then switch to the DOCTYPE public identifier (single-quoted) state.
U+003E GREATER-THAN SIGN (>)
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Parse error. Set the DOCTYPE token's force-quirks flag to on. Switch to the bogus DOCTYPE state.
8.2.4.28 DOCTYPE public identifier (double-quoted) state

Consume the next input character:

U+0022 QUOTATION MARK (")
Switch to the after DOCTYPE public identifier state.
U+003E GREATER-THAN SIGN (>)
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's public identifier. Stay in the DOCTYPE public identifier (double-quoted) state.
8.2.4.29 DOCTYPE public identifier (single-quoted) state

Consume the next input character:

U+0027 APOSTROPHE (')
Switch to the after DOCTYPE public identifier state.
U+003E GREATER-THAN SIGN (>)
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's public identifier. Stay in the DOCTYPE public identifier (single-quoted) state.
8.2.4.30 After DOCTYPE public identifier state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the after DOCTYPE public identifier state.
U+0022 QUOTATION MARK (")
Set the DOCTYPE token's system identifier to the empty string (not missing), then switch to the DOCTYPE system identifier (double-quoted) state.
U+0027 APOSTROPHE (')
Set the DOCTYPE token's system identifier to the empty string (not missing), then switch to the DOCTYPE system identifier (single-quoted) state.
U+003E GREATER-THAN SIGN (>)
Emit the current DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Parse error. Set the DOCTYPE token's force-quirks flag to on. Switch to the bogus DOCTYPE state.
8.2.4.31 Before DOCTYPE system identifier state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before DOCTYPE system identifier state.
U+0022 QUOTATION MARK (")
Set the DOCTYPE token's system identifier to the empty string (not missing), then switch to the DOCTYPE system identifier (double-quoted) state.
U+0027 APOSTROPHE (')
Set the DOCTYPE token's system identifier to the empty string (not missing), then switch to the DOCTYPE system identifier (single-quoted) state.
U+003E GREATER-THAN SIGN (>)
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Parse error. Set the DOCTYPE token's force-quirks flag to on. Switch to the bogus DOCTYPE state.
8.2.4.32 DOCTYPE system identifier (double-quoted) state

Consume the next input character:

U+0022 QUOTATION MARK (")
Switch to the after DOCTYPE system identifier state.
U+003E GREATER-THAN SIGN (>)
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's system identifier. Stay in the DOCTYPE system identifier (double-quoted) state.
8.2.4.33 DOCTYPE system identifier (single-quoted) state

Consume the next input character:

U+0027 APOSTROPHE (')
Switch to the after DOCTYPE system identifier state.
U+003E GREATER-THAN SIGN (>)
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's system identifier. Stay in the DOCTYPE system identifier (single-quoted) state.
8.2.4.34 After DOCTYPE system identifier state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the after DOCTYPE system identifier state.
U+003E GREATER-THAN SIGN (>)
Emit the current DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's force-quirks flag to on. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Parse error. Switch to the bogus DOCTYPE state. (This does not set the DOCTYPE token's force-quirks flag to on.)
8.2.4.35 Bogus DOCTYPE state

Consume the next input character:

U+003E GREATER-THAN SIGN (>)
Emit the DOCTYPE token. Switch to the data state.
EOF
Emit the DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Stay in the bogus DOCTYPE state.
8.2.4.36 CDATA section state

(This can only happen if the content model flag is set to the PCDATA state, and is unrelated to the content model flag's CDATA state.)

Consume every character up to the next occurrence of the three character sequence U+005D RIGHT SQUARE BRACKET U+005D RIGHT SQUARE BRACKET U+003E GREATER-THAN SIGN (]]>), or the end of the file (EOF), whichever comes first. Emit a series of character tokens consisting of all the characters consumed except the matching three character sequence at the end (if one was found before the end of the file).

Switch to the data state.

If the end of the file was reached, reconsume the EOF character.

8.2.4.37 Tokenizing character references

This section defines how to consume a character reference. This definition is used when parsing character references in text and in attributes.

The behavior depends on the identity of the next character (the one immediately after the U+0026 AMPERSAND character):

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+0020 SPACE
U+003C LESS-THAN SIGN
U+0026 AMPERSAND
EOF
The additional allowed character, if there is one
Not a character reference. No characters are consumed, and nothing is returned. (This is not an error, either.)
U+0023 NUMBER SIGN (#)

Consume the U+0023 NUMBER SIGN.

The behavior further depends on the character after the U+0023 NUMBER SIGN:

U+0078 LATIN SMALL LETTER X
U+0058 LATIN CAPITAL LETTER X

Consume the X.

Follow the steps below, but using the range of characters U+0030 DIGIT ZERO through to U+0039 DIGIT NINE, U+0061 LATIN SMALL LETTER A through to U+0066 LATIN SMALL LETTER F, and U+0041 LATIN CAPITAL LETTER A, through to U+0046 LATIN CAPITAL LETTER F (in other words, 0-9, A-F, a-f).

When it comes to interpreting the number, interpret it as a hexadecimal number.

Anything else

Follow the steps below, but using the range of characters U+0030 DIGIT ZERO through to U+0039 DIGIT NINE (i.e. just 0-9).

When it comes to interpreting the number, interpret it as a decimal number.

Consume as many characters as match the range of characters given above.

If no characters match the range, then don't consume any characters (and unconsume the U+0023 NUMBER SIGN character and, if appropriate, the X character). This is a parse error; nothing is returned.

Otherwise, if the next character is a U+003B SEMICOLON, consume that too. If it isn't, there is a parse error.

If one or more characters match the range, then take them all and interpret the string of characters as a number (either hexadecimal or decimal as appropriate).

If that number is one of the numbers in the first column of the following table, then this is a parse error. Find the row with that number in the first column, and return a character token for the Unicode character given in the second column of that row.

Number Unicode character
0x0D U+000A LINE FEED (LF)
0x80 U+20AC EURO SIGN ('€')
0x81 U+FFFD REPLACEMENT CHARACTER
0x82 U+201A SINGLE LOW-9 QUOTATION MARK ('‚')
0x83 U+0192 LATIN SMALL LETTER F WITH HOOK ('ƒ')
0x84 U+201E DOUBLE LOW-9 QUOTATION MARK ('„')
0x85 U+2026 HORIZONTAL ELLIPSIS ('…')
0x86 U+2020 DAGGER ('†')
0x87 U+2021 DOUBLE DAGGER ('‡')
0x88 U+02C6 MODIFIER LETTER CIRCUMFLEX ACCENT ('ˆ')
0x89 U+2030 PER MILLE SIGN ('‰')
0x8A U+0160 LATIN CAPITAL LETTER S WITH CARON ('Š')
0x8B U+2039 SINGLE LEFT-POINTING ANGLE QUOTATION MARK ('‹')
0x8C U+0152 LATIN CAPITAL LIGATURE OE ('Œ')
0x8D U+FFFD REPLACEMENT CHARACTER
0x8E U+017D LATIN CAPITAL LETTER Z WITH CARON ('Ž')
0x8F U+FFFD REPLACEMENT CHARACTER
0x90 U+FFFD REPLACEMENT CHARACTER
0x91 U+2018 LEFT SINGLE QUOTATION MARK ('‘')
0x92 U+2019 RIGHT SINGLE QUOTATION MARK ('’')
0x93 U+201C LEFT DOUBLE QUOTATION MARK ('“')
0x94 U+201D RIGHT DOUBLE QUOTATION MARK ('”')
0x95 U+2022 BULLET ('•')
0x96 U+2013 EN DASH ('–')
0x97 U+2014 EM DASH ('—')
0x98 U+02DC SMALL TILDE ('˜')
0x99 U+2122 TRADE MARK SIGN ('™')
0x9A U+0161 LATIN SMALL LETTER S WITH CARON ('š')
0x9B U+203A SINGLE RIGHT-POINTING ANGLE QUOTATION MARK ('›')
0x9C U+0153 LATIN SMALL LIGATURE OE ('œ')
0x9D U+FFFD REPLACEMENT CHARACTER
0x9E U+017E LATIN SMALL LETTER Z WITH CARON ('ž')
0x9F U+0178 LATIN CAPITAL LETTER Y WITH DIAERESIS ('Ÿ')

Otherwise, if the number is in the range 0x0000 to 0x0008, 0x000E to 0x001F, 0x007F to 0x009F, 0xD800 to 0xDFFF, 0xFDD0 to 0xFDEF, or is one of 0x000B, 0xFFFE, 0xFFFF, 0x1FFFE, 0x1FFFF, 0x2FFFE, 0x2FFFF, 0x3FFFE, 0x3FFFF, 0x4FFFE, 0x4FFFF, 0x5FFFE, 0x5FFFF, 0x6FFFE, 0x6FFFF, 0x7FFFE, 0x7FFFF, 0x8FFFE, 0x8FFFF, 0x9FFFE, 0x9FFFF, 0xAFFFE, 0xAFFFF, 0xBFFFE, 0xBFFFF, 0xCFFFE, 0xCFFFF, 0xDFFFE, 0xDFFFF, 0xEFFFE, 0xEFFFF, 0xFFFFE, 0xFFFFF, 0x10FFFE, or 0x10FFFF, or is higher than 0x10FFFF, then this is a parse error; return a character token for the U+FFFD REPLACEMENT CHARACTER character instead.

Otherwise, return a character token for the Unicode character whose code point is that number.

Anything else

Consume the maximum number of characters possible, with the consumed characters matching one of the identifiers in the first column of the named character references table (in a case-sensitive manner).

If no match can be made, then this is a parse error. No characters are consumed, and nothing is returned.

If the last character matched is not a U+003B SEMICOLON (;), there is a parse error.

If the character reference is being consumed as part of an attribute, and the last character matched is not a U+003B SEMICOLON (;), and the next character is in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, U+0041 LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z, or U+0061 LATIN SMALL LETTER A to U+007A LATIN SMALL LETTER Z, then, for historical reasons, all the characters that were matched after the U+0026 AMPERSAND (&) must be unconsumed, and nothing is returned.

Otherwise, return a character token for the character corresponding to the character reference name (as given by the second column of the named character references table).

If the markup contains I'm &notit; I tell you, the character reference is parsed as "not", as in, I'm ¬it; I tell you. But if the markup was I'm &notin; I tell you, the character reference would be parsed as "notin;", resulting in I'm ∉ I tell you.

8.2.5 Tree construction

The input to the tree construction stage is a sequence of tokens from the tokenization stage. The tree construction stage is associated with a DOM Document object when a parser is created. The "output" of this stage consists of dynamically modifying or extending that document's DOM tree.

This specification does not define when an interactive user agent has to render the Document so that it is available to the user, or when it has to begin accepting user input.

As each token is emitted from the tokenizer, the user agent must process the token according to the rules given in the section corresponding to the current insertion mode.

When the steps below require the UA to insert a character into a node, if that node has a child immediately before where the character is to be inserted, and that child is a Text node, and that Text node was the last node that the parser inserted into the document, then the character must be appended to that Text node; otherwise, a new Text node whose data is just that character must be inserted in the appropriate place.

Here are some sample inputs to the parser and the corresponding number of text nodes that they result in, assuming a user agent that executes scripts.

Input Number of text nodes
A<script>
var script = document.getElementsByTagName('script')[0];
document.body.removeChild(script);
</script>B
Two adjacent text nodes in the document, containing "A" and "B".
A<script>
var text = document.createTextNode('B');
document.body.appendChild(text);
</script>C
Four text nodes; "A" before the script, the script's contents, "B" after the script, and then, immediately after that, "C".
A<script>
var text = document.getElementsByTagName('script')[0].firstChild;
text.data = 'B';
document.body.appendChild(text);
</script>B
Two adjacent text nodes in the document, containing "A" and "BB".
A<table>B<tr>C</tr>C</table>
Three adjacent text nodes before the table, containing "A", "B", and "CC" respectively. (This is caused by foster parenting.)
A<table><tr> B</tr> B</table>
Two adjacent text nodes before the table, containing "A" and "B B" respectively, and one text node inside the table with a single space character. (This is caused by foster parenting and tainting.)

DOM mutation events must not fire for changes caused by the UA parsing the document. (Conceptually, the parser is not mutating the DOM, it is constructing it.) This includes the parsing of any content inserted using document.write() and document.writeln() calls. [DOM3EVENTS]

Not all of the tag names mentioned below are conformant tag names in this specification; many are included to handle legacy content. They still form part of the algorithm that implementations are required to implement to claim conformance.

The algorithm described below places no limit on the depth of the DOM tree generated, or on the length of tag names, attribute names, attribute values, text nodes, etc. While implementors are encouraged to avoid arbitrary limits, it is recognized that practical concerns will likely force user agents to impose nesting depths.

8.2.5.1 Creating and inserting elements

When the steps below require the UA to create an element for a token in a particular namespace, the UA must create a node implementing the interface appropriate for the element type corresponding to the tag name of the token in the given namespace (as given in the specification that defines that element, e.g. for an a element in the HTML namespace, this specification defines it to be the HTMLAnchorElement interface), with the tag name being the name of that element, with the node being in the given namespace, and with the attributes on the node being those given in the given token.

The interface appropriate for an element in the HTML namespace that is not defined in this specification is HTMLElement. Element in other namespaces whose interface is not defined by that namespace's specification must use the interface Element.

When a resettable element is created in this manner, its reset algorithm must be invoked once the attributes are set. (This initializes the element's value and checkedness based on the element's attributes.)


When the steps below require the UA to insert an HTML element for a token, the UA must first create an element for the token in the HTML namespace, and then append this node to the current node, and push it onto the stack of open elements so that it is the new current node.

The steps below may also require that the UA insert an HTML element in a particular place, in which case the UA must follow the same steps except that it must insert or append the new node in the location specified instead of appending it to the current node. (This happens in particular during the parsing of tables with invalid content.)

If an element created by the insert an HTML element algorithm is a form-associated element, and the form element pointer is not null, and the newly created element doesn't have a form attribute, the user agent must associate the newly created element with the form element pointed to by the form element pointer before inserting it wherever it is to be inserted.


When the steps below require the UA to insert a foreign element for a token, the UA must first create an element for the token in the given namespace, and then append this node to the current node, and push it onto the stack of open elements so that it is the new current node. If the newly created element has an xmlns attribute in the XMLNS namespace whose value is not exactly the same as the element's namespace, that is a parse error. Similarly, if the newly created element has an xmlns:xlink attribute in the XMLNS namespace whose value is not the XLink Namespace, that is a parse error.

When the steps below require the user agent to adjust MathML attributes for a token, then, if the token has an attribute named definitionurl, change its name to definitionURL (note the case difference).

When the steps below require the user agent to adjust SVG attributes for a token, then, for each attribute on the token whose attribute name is one of the ones in the first column of the following table, change the attribute's name to the name given in the corresponding cell in the second column. (This fixes the case of SVG attributes that are not all lowercase.)

Attribute name on token Attribute name on element
attributename attributeName
attributetype attributeType
basefrequency baseFrequency
baseprofile baseProfile
calcmode calcMode
clippathunits clipPathUnits
contentscripttype contentScriptType
contentstyletype contentStyleType
diffuseconstant diffuseConstant
edgemode edgeMode
externalresourcesrequired externalResourcesRequired
filterres filterRes
filterunits filterUnits
glyphref glyphRef
gradienttransform gradientTransform
gradientunits gradientUnits
kernelmatrix kernelMatrix
kernelunitlength kernelUnitLength
keypoints keyPoints
keysplines keySplines
keytimes keyTimes
lengthadjust lengthAdjust
limitingconeangle limitingConeAngle
markerheight markerHeight
markerunits markerUnits
markerwidth markerWidth
maskcontentunits maskContentUnits
maskunits maskUnits
numoctaves numOctaves
pathlength pathLength
patterncontentunits patternContentUnits
patterntransform patternTransform
patternunits patternUnits
pointsatx pointsAtX
pointsaty pointsAtY
pointsatz pointsAtZ
preservealpha preserveAlpha
preserveaspectratio preserveAspectRatio
primitiveunits primitiveUnits
refx refX
refy refY
repeatcount repeatCount
repeatdur repeatDur
requiredextensions requiredExtensions
requiredfeatures requiredFeatures
specularconstant specularConstant
specularexponent specularExponent
spreadmethod spreadMethod
startoffset startOffset
stddeviation stdDeviation
stitchtiles stitchTiles
surfacescale surfaceScale
systemlanguage systemLanguage
tablevalues tableValues
targetx targetX
targety targetY
textlength textLength
viewbox viewBox
viewtarget viewTarget
xchannelselector xChannelSelector
ychannelselector yChannelSelector
zoomandpan zoomAndPan

When the steps below require the user agent to adjust foreign attributes for a token, then, if any of the attributes on the token match the strings given in the first column of the following table, let the attribute be a namespaced attribute, with the prefix being the string given in the corresponding cell in the second column, the local name being the string given in the corresponding cell in the third column, and the namespace being the namespace given in the corresponding cell in the fourth column. (This fixes the use of namespaced attributes, in particular xml:lang.)

Attribute name Prefix Local name Namespace
xlink:actuate xlink actuate XLink namespace
xlink:arcrole xlink arcrole XLink namespace
xlink:href xlink href XLink namespace
xlink:role xlink role XLink namespace
xlink:show xlink show XLink namespace
xlink:title xlink title XLink namespace
xlink:type xlink type XLink namespace
xml:base xml base XML namespace
xml:lang xml lang XML namespace
xml:space xml space XML namespace
xmlns (none) xmlns XMLNS namespace
xmlns:xlink xmlns xlink XMLNS namespace

The generic CDATA element parsing algorithm and the generic RCDATA element parsing algorithm consist of the following steps. These algorithms are always invoked in response to a start tag token.

  1. Insert an HTML element for the token.

  2. If the algorithm that was invoked is the generic CDATA element parsing algorithm, switch the tokenizer's content model flag to the CDATA state; otherwise the algorithm invoked was the generic RCDATA element parsing algorithm, switch the tokenizer's content model flag to the RCDATA state.

  3. Let the original insertion mode be the current insertion mode.

  4. Then, switch the insertion mode to "in CDATA/RCDATA".

8.2.5.2 Closing elements that have implied end tags

When the steps below require the UA to generate implied end tags, then, while the current node is a dd element, a dt element, an li element, an option element, an optgroup element, a p element, an rp element, or an rt element, the UA must pop the current node off the stack of open elements.

If a step requires the UA to generate implied end tags but lists an element to exclude from the process, then the UA must perform the above steps as if that element was not in the above list.

8.2.5.3 Foster parenting

Foster parenting happens when content is misnested in tables.

When a node node is to be foster parented, the node node must be inserted into the foster parent element, and the current table must be marked as tainted. (Once the current table has been tainted, whitespace characters are inserted into the foster parent element instead of the current node.)

The foster parent element is the parent element of the last table element in the stack of open elements, if there is a table element and it has such a parent element. If there is no table element in the stack of open elements (fragment case), then the foster parent element is the first element in the stack of open elements (the html element). Otherwise, if there is a table element in the stack of open elements, but the last table element in the stack of open elements has no parent, or its parent node is not an element, then the foster parent element is the element before the last table element in the stack of open elements.

If the foster parent element is the parent element of the last table element in the stack of open elements, then node must be inserted immediately before the last table element in the stack of open elements in the foster parent element; otherwise, node must be appended to the foster parent element.

8.2.5.4 The "initial" insertion mode

When the insertion mode is "initial", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Ignore the token.

A comment token

Append a Comment node to the Document object with the data attribute set to the data given in the comment token.

A DOCTYPE token

If the DOCTYPE token's name is not a case-sensitive match for the string "html", or if the token's public identifier is not missing, or if the token's system identifier is neither missing nor a case-sensitive match for the string "about:legacy-compat", then there is a parse error (this is the DOCTYPE parse error). Conformance checkers may, instead of reporting this error, switch to a conformance checking mode for another language (e.g. based on the DOCTYPE token a conformance checker could recognize that the document is an HTML4-era document, and defer to an HTML4 conformance checker.)

Append a DocumentType node to the Document node, with the name attribute set to the name given in the DOCTYPE token, or the empty string if the name was missing; the publicId attribute set to the public identifier given in the DOCTYPE token, or the empty string if the public identifier was missing; the systemId attribute set to the system identifier given in the DOCTYPE token, or the empty string if the system identifier was missing; and the other attributes specific to DocumentType objects set to null and empty lists as appropriate. Associate the DocumentType node with the Document object so that it is returned as the value of the doctype attribute of the Document object.

Then, if the DOCTYPE token matches one of the conditions in the following list, then set the document to quirks mode:

  • The force-quirks flag is set to on.
  • The name is set to anything other than "HTML".
  • The public identifier starts with: "+//Silmaril//dtd html Pro v0r11 19970101//"
  • The public identifier starts with: "-//AdvaSoft Ltd//DTD HTML 3.0 asWedit + extensions//"
  • The public identifier starts with: "-//AS//DTD HTML 3.0 asWedit + extensions//"
  • The public identifier starts with: "-//IETF//DTD HTML 2.0 Level 1//"
  • The public identifier starts with: "-//IETF//DTD HTML 2.0 Level 2//"
  • The public identifier starts with: "-//IETF//DTD HTML 2.0 Strict Level 1//"
  • The public identifier starts with: "-//IETF//DTD HTML 2.0 Strict Level 2//"
  • The public identifier starts with: "-//IETF//DTD HTML 2.0 Strict//"
  • The public identifier starts with: "-//IETF//DTD HTML 2.0//"
  • The public identifier starts with: "-//IETF//DTD HTML 2.1E//"
  • The public identifier starts with: "-//IETF//DTD HTML 3.0//"
  • The public identifier starts with: "-//IETF//DTD HTML 3.2 Final//"
  • The public identifier starts with: "-//IETF//DTD HTML 3.2//"
  • The public identifier starts with: "-//IETF//DTD HTML 3//"
  • The public identifier starts with: "-//IETF//DTD HTML Level 0//"
  • The public identifier starts with: "-//IETF//DTD HTML Level 1//"
  • The public identifier starts with: "-//IETF//DTD HTML Level 2//"
  • The public identifier starts with: "-//IETF//DTD HTML Level 3//"
  • The public identifier starts with: "-//IETF//DTD HTML Strict Level 0//"
  • The public identifier starts with: "-//IETF//DTD HTML Strict Level 1//"
  • The public identifier starts with: "-//IETF//DTD HTML Strict Level 2//"
  • The public identifier starts with: "-//IETF//DTD HTML Strict Level 3//"
  • The public identifier starts with: "-//IETF//DTD HTML Strict//"
  • The public identifier starts with: "-//IETF//DTD HTML//"
  • The public identifier starts with: "-//Metrius//DTD Metrius Presentational//"
  • The public identifier starts with: "-//Microsoft//DTD Internet Explorer 2.0 HTML Strict//"
  • The public identifier starts with: "-//Microsoft//DTD Internet Explorer 2.0 HTML//"
  • The public identifier starts with: "-//Microsoft//DTD Internet Explorer 2.0 Tables//"
  • The public identifier starts with: "-//Microsoft//DTD Internet Explorer 3.0 HTML Strict//"
  • The public identifier starts with: "-//Microsoft//DTD Internet Explorer 3.0 HTML//"
  • The public identifier starts with: "-//Microsoft//DTD Internet Explorer 3.0 Tables//"
  • The public identifier starts with: "-//Netscape Comm. Corp.//DTD HTML//"
  • The public identifier starts with: "-//Netscape Comm. Corp.//DTD Strict HTML//"
  • The public identifier starts with: "-//O'Reilly and Associates//DTD HTML 2.0//"
  • The public identifier starts with: "-//O'Reilly and Associates//DTD HTML Extended 1.0//"
  • The public identifier starts with: "-//O'Reilly and Associates//DTD HTML Extended Relaxed 1.0//"
  • The public identifier starts with: "-//SoftQuad Software//DTD HoTMetaL PRO 6.0::19990601::extensions to HTML 4.0//"
  • The public identifier starts with: "-//SoftQuad//DTD HoTMetaL PRO 4.0::19971010::extensions to HTML 4.0//"
  • The public identifier starts with: "-//Spyglass//DTD HTML 2.0 Extended//"
  • The public identifier starts with: "-//SQ//DTD HTML 2.0 HoTMetaL + extensions//"
  • The public identifier starts with: "-//Sun Microsystems Corp.//DTD HotJava HTML//"
  • The public identifier starts with: "-//Sun Microsystems Corp.//DTD HotJava Strict HTML//"
  • The public identifier starts with: "-//W3C//DTD HTML 3 1995-03-24//"
  • The public identifier starts with: "-//W3C//DTD HTML 3.2 Draft//"
  • The public identifier starts with: "-//W3C//DTD HTML 3.2 Final//"
  • The public identifier starts with: "-//W3C//DTD HTML 3.2//"
  • The public identifier starts with: "-//W3C//DTD HTML 3.2S Draft//"
  • The public identifier starts with: "-//W3C//DTD HTML 4.0 Frameset//"
  • The public identifier starts with: "-//W3C//DTD HTML 4.0 Transitional//"
  • The public identifier starts with: "-//W3C//DTD HTML Experimental 19960712//"
  • The public identifier starts with: "-//W3C//DTD HTML Experimental 970421//"
  • The public identifier starts with: "-//W3C//DTD W3 HTML//"
  • The public identifier starts with: "-//W3O//DTD W3 HTML 3.0//"
  • The public identifier is set to: "-//W3O//DTD W3 HTML Strict 3.0//EN//"
  • The public identifier starts with: "-//WebTechs//DTD Mozilla HTML 2.0//"
  • The public identifier starts with: "-//WebTechs//DTD Mozilla HTML//"
  • The public identifier is set to: "-/W3C/DTD HTML 4.0 Transitional/EN"
  • The public identifier is set to: "HTML"
  • The system identifier is set to: "http://www.ibm.com/data/dtd/v11/ibmxhtml1-transitional.dtd"
  • The system identifier is missing and the public identifier starts with: "-//W3C//DTD HTML 4.01 Frameset//"
  • The system identifier is missing and the public identifier starts with: "-//W3C//DTD HTML 4.01 Transitional//"

Otherwise, if the DOCTYPE token matches one of the conditions in the following list, then set the document to limited quirks mode:

  • The public identifier starts with: "-//W3C//DTD XHTML 1.0 Frameset//"
  • The public identifier starts with: "-//W3C//DTD XHTML 1.0 Transitional//"
  • The system identifier is not missing and the public identifier starts with: "-//W3C//DTD HTML 4.01 Frameset//"
  • The system identifier is not missing and the public identifier starts with: "-//W3C//DTD HTML 4.01 Transitional//"

The name, system identifier, and public identifier strings must be compared to the values given in the lists above in an ASCII case-insensitive manner. A system identifier whose value is the empty string is not considered missing for the purposes of the conditions above.

Then, switch the insertion mode to "before html".

Anything else

Parse error.

Set the document to quirks mode.

Switch the insertion mode to "before html", then reprocess the current token.

8.2.5.5 The "before html" insertion mode

When the insertion mode is "before html", tokens must be handled as follows:

A DOCTYPE token

Parse error. Ignore the token.

A comment token

Append a Comment node to the Document object with the data attribute set to the data given in the comment token.

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Ignore the token.

A start tag whose tag name is "html"

Create an element for the token in the HTML namespace. Append it to the Document object. Put this element in the stack of open elements.

If the Document is being loaded as part of navigation of a browsing context, then: if the newly created element has a manifest attribute, then resolve the value of that attribute to an absolute URL, relative to the newly created element, and if that is successful, run the application cache selection algorithm with the resulting absolute URL; otherwise, if there is no such attribute or resolving it fails, run the application cache selection algorithm with no manifest. The algorithm must be passed the Document object.

Switch the insertion mode to "before head".

Anything else

Create an html element. Append it to the Document object. Put this element in the stack of open elements.

If the Document is being loaded as part of navigation of a browsing context, then: run the application cache selection algorithm with no manifest, passing it the Document object.

Switch the insertion mode to "before head", then reprocess the current token.

Should probably make end tags be ignored, so that "</head><!-- --><html>" puts the comment before the root node (or should we?)

The root element can end up being removed from the Document object, e.g. by scripts; nothing in particular happens in such cases, content continues being appended to the nodes as described in the next section.

8.2.5.6 The "before head" insertion mode

When the insertion mode is "before head", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Ignore the token.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

A start tag whose tag name is "head"

Insert an HTML element for the token.

Set the head element pointer to the newly created head element.

Switch the insertion mode to "in head".

An end tag whose tag name is one of: "head", "body", "html", "br"

Act as if a start tag token with the tag name "head" and no attributes had been seen, then reprocess the current token.

Any other end tag

Parse error. Ignore the token.

Anything else

Act as if a start tag token with the tag name "head" and no attributes had been seen, then reprocess the current token.

This will result in an empty head element being generated, with the current token being reprocessed in the "after head" insertion mode.

8.2.5.7 The "in head" insertion mode

When the insertion mode is "in head", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Insert the character into the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

A start tag whose tag name is one of: "base", "command", "link"

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

Acknowledge the token's self-closing flag, if it is set.

A start tag whose tag name is "meta"

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

Acknowledge the token's self-closing flag, if it is set.

If the element has a charset attribute, and its value is a supported encoding, and the confidence is currently tentative, then change the encoding to the encoding given by the value of the charset attribute.

Otherwise, if the element has a content attribute, and applying the algorithm for extracting an encoding from a Content-Type to its value returns a supported encoding encoding, and the confidence is currently tentative, then change the encoding to the encoding encoding.

A start tag whose tag name is "title"

Follow the generic RCDATA element parsing algorithm.

A start tag whose tag name is "noscript", if the scripting flag is enabled
A start tag whose tag name is one of: "noframes", "style"

Follow the generic CDATA element parsing algorithm.

A start tag whose tag name is "noscript", if the scripting flag is disabled

Insert an HTML element for the token.

Switch the insertion mode to "in head noscript".

A start tag whose tag name is "script"
  1. Create an element for the token in the HTML namespace.

  2. Mark the element as being "parser-inserted".

    This ensures that, if the script is external, any document.write() calls in the script will execute in-line, instead of blowing the document away, as would happen in most other cases. It also prevents the script from executing until the end tag is seen.

  3. If the parser was originally created for the HTML fragment parsing algorithm, then mark the script element as "already executed". (fragment case)

  4. Append the new element to the current node and push it onto the stack of open elements.

  5. Switch the tokenizer's content model flag to the CDATA state.

  6. Let the original insertion mode be the current insertion mode.

  7. Switch the insertion mode to "in CDATA/RCDATA".

An end tag whose tag name is "head"

Pop the current node (which will be the head element) off the stack of open elements.

Switch the insertion mode to "after head".

An end tag whose tag name is one of: "body", "html", "br"

Act as described in the "anything else" entry below.

A start tag whose tag name is "head"
Any other end tag

Parse error. Ignore the token.

Anything else

Act as if an end tag token with the tag name "head" had been seen, and reprocess the current token.

In certain UAs, some elements don't trigger the "in body" mode straight away, but instead get put into the head. Do we want to copy that?

8.2.5.8 The "in head noscript" insertion mode

When the insertion mode is "in head noscript", tokens must be handled as follows:

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

An end tag whose tag name is "noscript"

Pop the current node (which will be a noscript element) from the stack of open elements; the new current node will be a head element.

Switch the insertion mode to "in head".

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE
A comment token
A start tag whose tag name is one of: "link", "meta", "noframes", "style"

Process the token using the rules for the "in head" insertion mode.

An end tag whose tag name is "br"

Act as described in the "anything else" entry below.

A start tag whose tag name is one of: "head", "noscript"
Any other end tag

Parse error. Ignore the token.

Anything else

Parse error. Act as if an end tag with the tag name "noscript" had been seen and reprocess the current token.

8.2.5.9 The "after head" insertion mode

When the insertion mode is "after head", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Insert the character into the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

A start tag whose tag name is "body"

Insert an HTML element for the token.

Set the frameset-ok flag to "not ok".

Switch the insertion mode to "in body".

A start tag whose tag name is "frameset"

Insert an HTML element for the token.

Switch the insertion mode to "in frameset".

A start tag token whose tag name is one of: "base", "link", "meta", "noframes", "script", "style", "title"

Parse error.

Push the node pointed to by the head element pointer onto the stack of open elements.

Process the token using the rules for the "in head" insertion mode.

Remove the node pointed to by the head element pointer from the stack of open elements.

The head element pointer cannot be null at this point.

An end tag whose tag name is one of: "body", "html", "br"

Act as described in the "anything else" entry below.

A start tag whose tag name is "head"
Any other end tag

Parse error. Ignore the token.

Anything else

Act as if a start tag token with the tag name "body" and no attributes had been seen, then set the frameset-ok flag back to "ok", and then reprocess the current token.

8.2.5.10 The "in body" insertion mode

When the insertion mode is "in body", tokens must be handled as follows:

A character token

Reconstruct the active formatting elements, if any.

Insert the token's character into the current node.

If the token is not one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE, then set the frameset-ok flag to "not ok".

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Parse error. For each attribute on the token, check to see if the attribute is already present on the top element of the stack of open elements. If it is not, add the attribute and its corresponding value to that element.

A start tag token whose tag name is one of: "base", "command", "link", "meta", "noframes", "script", "style", "title"

Process the token using the rules for the "in head" insertion mode.

A start tag whose tag name is "body"

Parse error.

If the second element on the stack of open elements is not a body element, or, if the stack of open elements has only one node on it, then ignore the token. (fragment case)

Otherwise, for each attribute on the token, check to see if the attribute is already present on the body element (the second element) on the stack of open elements. If it is not, add the attribute and its corresponding value to that element.

A start tag whose tag name is "frameset"

Parse error.

If the second element on the stack of open elements is not a body element, or, if the stack of open elements has only one node on it, then ignore the token. (fragment case)

If the frameset-ok flag is set to "not ok", ignore the token.

Otherwise, run the following steps:

  1. Remove the second element on the stack of open elements from its parent node, if it has one.

  2. Pop all the nodes from the bottom of the stack of open elements, from the current node up to the root html element.

  3. Insert an HTML element for the token.

  4. Switch the insertion mode to "in frameset".

An end-of-file token

If there is a node in the stack of open elements that is not either a dd element, a dt element, an li element, a p element, a tbody element, a td element, a tfoot element, a th element, a thead element, a tr element, the body element, or the html element, then this is a parse error.

Stop parsing.

An end tag whose tag name is "body"

If the stack of open elements does not have a body element in scope, this is a parse error; ignore the token.

Otherwise, if there is a node in the stack of open elements that is not either a dd element, a dt element, an li element, an optgroup element, an option element, a p element, an rp element, an rt element, a tbody element, a td element, a tfoot element, a th element, a thead element, a tr element, the body element, or the html element, then this is a parse error.

Switch the insertion mode to "after body".

An end tag whose tag name is "html"

Act as if an end tag with tag name "body" had been seen, then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

A start tag whose tag name is one of: "address", "article", "aside", "blockquote", "center", "datagrid", "details", "dialog", "dir", "div", "dl", "fieldset", "figure", "footer", "header", "hgroup", "menu", "nav", "ol", "p", "section", "ul"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

Insert an HTML element for the token.

A start tag whose tag name is one of: "h1", "h2", "h3", "h4", "h5", "h6"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

If the current node is an element whose tag name is one of "h1", "h2", "h3", "h4", "h5", or "h6", then this is a parse error; pop the current node off the stack of open elements.

Insert an HTML element for the token.

A start tag whose tag name is one of: "pre", "listing"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

Insert an HTML element for the token.

If the next token is a U+000A LINE FEED (LF) character token, then ignore that token and move on to the next one. (Newlines at the start of pre blocks are ignored as an authoring convenience.)

Set the frameset-ok flag to "not ok".

A start tag whose tag name is "form"

If the form element pointer is not null, then this is a parse error; ignore the token.

Otherwise:

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

Insert an HTML element for the token, and set the form element pointer to point to the element created.

A start tag whose tag name is "li"

Run the following algorithm:

  1. Set the frameset-ok flag to "not ok".

  2. Initialize node to be the current node (the bottommost node of the stack).

  3. If node is an li element, then act as if an end tag with the tag name "li" had been seen, then jump to the last step.

  4. If node is not in the formatting category, and is not in the phrasing category, and is not an address, div, or p element, then jump to the last step.

  5. Otherwise, set node to the previous entry in the stack of open elements and return to step 2.

  6. This is the last step.

    If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

    Finally, insert an HTML element for the token.

A start tag whose tag name is one of: "dd", "dt"

Run the following algorithm:

  1. Set the frameset-ok flag to "not ok".

  2. Initialize node to be the current node (the bottommost node of the stack).

  3. If node is a dd or dt element, then act as if an end tag with the same tag name as node had been seen, then jump to the last step.

  4. If node is not in the formatting category, and is not in the phrasing category, and is not an address, div, or p element, then jump to the last step.

  5. Otherwise, set node to the previous entry in the stack of open elements and return to step 2.

  6. This is the last step.

    If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

    Finally, insert an HTML element for the token.

A start tag whose tag name is "plaintext"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

Insert an HTML element for the token.

Switch the content model flag to the PLAINTEXT state.

Once a start tag with the tag name "plaintext" has been seen, that will be the last token ever seen other than character tokens (and the end-of-file token), because there is no way to switch the content model flag out of the PLAINTEXT state.

An end tag whose tag name is one of: "address", "article", "aside", "blockquote", "center", "datagrid", "details", "dialog", "dir", "div", "dl", "fieldset", "figure", "footer", "header", "hgroup", "listing", "menu", "nav", "ol", "pre", "section", "ul"

If the stack of open elements does not have an element in scope with the same tag name as that of the token, then this is a parse error; ignore the token.

Otherwise, run these steps:

  1. Generate implied end tags.

  2. If the current node is not an element with the same tag name as that of the token, then this is a parse error.

  3. Pop elements from the stack of open elements until an element with the same tag name as the token has been popped from the stack.

An end tag whose tag name is "form"

Let node be the element that the form element pointer is set to.

Set the form element pointer to null.

If node is null or the stack of open elements does not have node in scope, then this is a parse error; ignore the token.

Otherwise, run these steps:

  1. Generate implied end tags.

  2. If the current node is not node, then this is a parse error.

  3. Remove node from the stack of open elements.

An end tag whose tag name is "p"

If the stack of open elements does not have an element in scope with the same tag name as that of the token, then this is a parse error; act as if a start tag with the tag name "p" had been seen, then reprocess the current token.

Otherwise, run these steps:

  1. Generate implied end tags, except for elements with the same tag name as the token.

  2. If the current node is not an element with the same tag name as that of the token, then this is a parse error.

  3. Pop elements from the stack of open elements until an element with the same tag name as the token has been popped from the stack.

An end tag whose tag name is one of: "dd", "dt", "li"

If the stack of open elements does not have an element in scope with the same tag name as that of the token, then this is a parse error; ignore the token.

Otherwise, run these steps:

  1. Generate implied end tags, except for elements with the same tag name as the token.

  2. If the current node is not an element with the same tag name as that of the token, then this is a parse error.

  3. Pop elements from the stack of open elements until an element with the same tag name as the token has been popped from the stack.

An end tag whose tag name is one of: "h1", "h2", "h3", "h4", "h5", "h6"

If the stack of open elements does not have an element in scope whose tag name is one of "h1", "h2", "h3", "h4", "h5", or "h6", then this is a parse error; ignore the token.

Otherwise, run these steps:

  1. Generate implied end tags.

  2. If the current node is not an element with the same tag name as that of the token, then this is a parse error.

  3. Pop elements from the stack of open elements until an element whose tag name is one of "h1", "h2", "h3", "h4", "h5", or "h6" has been popped from the stack.

An end tag whose tag name is "sarcasm"

Take a deep breath, then act as described in the "any other end tag" entry below.

A start tag whose tag name is "a"

If the list of active formatting elements contains an element whose tag name is "a" between the end of the list and the last marker on the list (or the start of the list if there is no marker on the list), then this is a parse error; act as if an end tag with the tag name "a" had been seen, then remove that element from the list of active formatting elements and the stack of open elements if the end tag didn't already remove it (it might not have if the element is not in table scope).

In the non-conforming stream <a href="a">a<table><a href="b">b</table>x, the first a element would be closed upon seeing the second one, and the "x" character would be inside a link to "b", not to "a". This is despite the fact that the outer a element is not in table scope (meaning that a regular </a> end tag at the start of the table wouldn't close the outer a element).

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token. Add that element to the list of active formatting elements.

A start tag whose tag name is one of: "b", "big", "code", "em", "font", "i", "s", "small", "strike", "strong", "tt", "u"

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token. Add that element to the list of active formatting elements.

A start tag whose tag name is "nobr"

Reconstruct the active formatting elements, if any.

If the stack of open elements has a nobr element in scope, then this is a parse error; act as if an end tag with the tag name "nobr" had been seen, then once again reconstruct the active formatting elements, if any.

Insert an HTML element for the token. Add that element to the list of active formatting elements.

An end tag whose tag name is one of: "a", "b", "big", "code", "em", "font", "i", "nobr", "s", "small", "strike", "strong", "tt", "u"

Follow these steps:

  1. Let the formatting element be the last element in the list of active formatting elements that:

    • is between the end of the list and the last scope marker in the list, if any, or the start of the list otherwise, and
    • has the same tag name as the token.

    If there is no such node, or, if that node is also in the stack of open elements but the element is not in scope, then this is a parse error; ignore the token, and abort these steps.

    Otherwise, if there is such a node, but that node is not in the stack of open elements, then this is a parse error; remove the element from the list, and abort these steps.

    Otherwise, there is a formatting element and that element is in the stack and is in scope. If the element is not the current node, this is a parse error. In any case, proceed with the algorithm as written in the following steps.

  2. Let the furthest block be the topmost node in the stack of open elements that is lower in the stack than the formatting element, and is not an element in the phrasing or formatting categories. There might not be one.

  3. If there is no furthest block, then the UA must skip the subsequent steps and instead just pop all the nodes from the bottom of the stack of open elements, from the current node up to and including the formatting element, and remove the formatting element from the list of active formatting elements.

  4. Let the common ancestor be the element immediately above the formatting element in the stack of open elements.

  5. Let a bookmark note the position of the formatting element in the list of active formatting elements relative to the elements on either side of it in the list.

  6. Let node and last node be the furthest block. Follow these steps:

    1. Let node be the element immediately above node in the stack of open elements.
    2. If node is not in the list of active formatting elements, then remove node from the stack of open elements and then go back to step 1.
    3. Otherwise, if node is the formatting element, then go to the next step in the overall algorithm.
    4. Otherwise, if last node is the furthest block, then move the aforementioned bookmark to be immediately after the node in the list of active formatting elements.
    5. Create an element for the token for which the element node was created, replace the entry for node in the list of active formatting elements with an entry for the new element, replace the entry for node in the stack of open elements with an entry for the new element, and let node be the new element.
    6. Insert last node into node, first removing it from its previous parent node if any.
    7. Let last node be node.
    8. Return to step 1 of this inner set of steps.
  7. If the common ancestor node is a table, tbody, tfoot, thead, or tr element, then, foster parent whatever last node ended up being in the previous step, first removing it from its previous parent node if any.

    Otherwise, append whatever last node ended up being in the previous step to the common ancestor node, first removing it from its previous parent node if any.

  8. Create an element for the token for which the formatting element was created.

  9. Take all of the child nodes of the furthest block and append them to the element created in the last step.

  10. Append that new element to the furthest block.

  11. Remove the formatting element from the list of active formatting elements, and insert the new element into the list of active formatting elements at the position of the aforementioned bookmark.

  12. Remove the formatting element from the stack of open elements, and insert the new element into the stack of open elements immediately below the position of the furthest block in that stack.

  13. Jump back to step 1 in this series of steps.

Because of the way this algorithm causes elements to change parents, it has been dubbed the "adoption agency algorithm" (in contrast with other possibly algorithms for dealing with misnested content, which included the "incest algorithm", the "secret affair algorithm", and the "Heisenberg algorithm").

A start tag whose tag name is "button"

If the stack of open elements has a button element in scope, then this is a parse error; act as if an end tag with the tag name "button" had been seen, then reprocess the token.

Otherwise:

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

Insert a marker at the end of the list of active formatting elements.

Set the frameset-ok flag to "not ok".

A start tag token whose tag name is one of: "applet", "marquee", "object"

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

Insert a marker at the end of the list of active formatting elements.

Set the frameset-ok flag to "not ok".

An end tag token whose tag name is one of: "applet", "button", "marquee", "object"

If the stack of open elements does not have an element in scope with the same tag name as that of the token, then this is a parse error; ignore the token.

Otherwise, run these steps:

  1. Generate implied end tags.

  2. If the current node is not an element with the same tag name as that of the token, then this is a parse error.

  3. Pop elements from the stack of open elements until an element with the same tag name as the token has been popped from the stack.

  4. Clear the list of active formatting elements up to the last marker.
A start tag whose tag name is "table"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

Insert an HTML element for the token.

Set the frameset-ok flag to "not ok".

Switch the insertion mode to "in table".

A start tag whose tag name is one of: "area", "basefont", "bgsound", "br", "embed", "img", "input", "keygen", "spacer", "wbr"

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

Acknowledge the token's self-closing flag, if it is set.

Set the frameset-ok flag to "not ok".

A start tag whose tag name is one of: "param", "source"

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

Acknowledge the token's self-closing flag, if it is set.

A start tag whose tag name is "hr"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

Acknowledge the token's self-closing flag, if it is set.

Set the frameset-ok flag to "not ok".

A start tag whose tag name is "image"

Parse error. Change the token's tag name to "img" and reprocess it. (Don't ask.)

A start tag whose tag name is "isindex"

Parse error.

If the form element pointer is not null, then ignore the token.

Otherwise:

Acknowledge the token's self-closing flag, if it is set.

Act as if a start tag token with the tag name "form" had been seen.

If the token has an attribute called "action", set the action attribute on the resulting form element to the value of the "action" attribute of the token.

Act as if a start tag token with the tag name "hr" had been seen.

Act as if a start tag token with the tag name "p" had been seen.

Act as if a start tag token with the tag name "label" had been seen.

Act as if a stream of character tokens had been seen (see below for what they should say).

Act as if a start tag token with the tag name "input" had been seen, with all the attributes from the "isindex" token except "name", "action", and "prompt". Set the name attribute of the resulting input element to the value "isindex".

Act as if a stream of character tokens had been seen (see below for what they should say).

Act as if an end tag token with the tag name "label" had been seen.

Act as if an end tag token with the tag name "p" had been seen.

Act as if a start tag token with the tag name "hr" had been seen.

Act as if an end tag token with the tag name "form" had been seen.

If the token has an attribute with the name "prompt", then the first stream of characters must be the same string as given in that attribute, and the second stream of characters must be empty. Otherwise, the two streams of character tokens together should, together with the input element, express the equivalent of "This is a searchable index. Insert your search keywords here: (input field)" in the user's preferred language.

A start tag whose tag name is "textarea"
  1. Insert an HTML element for the token.

  2. If the next token is a U+000A LINE FEED (LF) character token, then ignore that token and move on to the next one. (Newlines at the start of textarea elements are ignored as an authoring convenience.)

  3. Switch the tokenizer's content model flag to the RCDATA state.

  4. Let the original insertion mode be the current insertion mode.

  5. Set the frameset-ok flag to "not ok".

  6. Switch the insertion mode to "in CDATA/RCDATA".

A start tag whose tag name is "xmp"

Reconstruct the active formatting elements, if any.

Set the frameset-ok flag to "not ok".

Follow the generic CDATA element parsing algorithm.

A start tag whose tag name is "iframe"

Set the frameset-ok flag to "not ok".

Follow the generic CDATA element parsing algorithm.

A start tag whose tag name is "noembed"
A start tag whose tag name is "noscript", if the scripting flag is enabled

Follow the generic CDATA element parsing algorithm.

A start tag whose tag name is "select"

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

Set the frameset-ok flag to "not ok".

If the insertion mode is one of in table", "in caption", "in column group", "in table body", "in row", or "in cell", then switch the insertion mode to "in select in table". Otherwise, switch the insertion mode to "in select".

A start tag whose tag name is one of: "optgroup", "option"

If the stack of open elements has an option element in scope, then act as if an end tag with the tag name "option" had been seen.

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

A start tag whose tag name is one of: "rp", "rt"

If the stack of open elements has a ruby element in scope, then generate implied end tags. If the current node is not then a ruby element, this is a parse error; pop all the nodes from the current node up to the node immediately before the bottommost ruby element on the stack of open elements.

Insert an HTML element for the token.

An end tag whose tag name is "br"

Parse error. Act as if a start tag token with the tag name "br" had been seen. Ignore the end tag token.

A start tag whose tag name is "math"

Reconstruct the active formatting elements, if any.

Adjust MathML attributes for the token. (This fixes the case of MathML attributes that are not all lowercase.)

Adjust foreign attributes for the token. (This fixes the use of namespaced attributes, in particular XLink.)

Insert a foreign element for the token, in the MathML namespace.

If the token has its self-closing flag set, pop the current node off the stack of open elements and acknowledge the token's self-closing flag.

Otherwise, if the insertion mode is not already "in foreign content", let the secondary insertion mode be the current insertion mode, and then switch the insertion mode to "in foreign content".

A start tag whose tag name is "svg"

Reconstruct the active formatting elements, if any.

Adjust SVG attributes for the token. (This fixes the case of SVG attributes that are not all lowercase.)

Adjust foreign attributes for the token. (This fixes the use of namespaced attributes, in particular XLink in SVG.)

Insert a foreign element for the token, in the SVG namespace.

If the token has its self-closing flag set, pop the current node off the stack of open elements and acknowledge the token's self-closing flag.

Otherwise, if the insertion mode is not already "in foreign content", let the secondary insertion mode be the current insertion mode, and then switch the insertion mode to "in foreign content".

A start tag whose tag name is one of: "caption", "col", "colgroup", "frame", "head", "tbody", "td", "tfoot", "th", "thead", "tr"

Parse error. Ignore the token.

Any other start tag

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

This element will be a phrasing element.

Any other end tag

Run the following steps:

  1. Initialize node to be the current node (the bottommost node of the stack).

  2. If node has the same tag name as the end tag token, then:

    1. Generate implied end tags.

    2. If the tag name of the end tag token does not match the tag name of the current node, this is a parse error.

    3. Pop all the nodes from the current node up to node, including node, then stop these steps.

  3. Otherwise, if node is in neither the formatting category nor the phrasing category, then this is a parse error; ignore the token, and abort these steps.

  4. Set node to the previous entry in the stack of open elements.

  5. Return to step 2.

8.2.5.11 The "in CDATA/RCDATA" insertion mode

When the insertion mode is "in CDATA/RCDATA", tokens must be handled as follows:

A character token

Insert the token's character into the current node.

An end-of-file token

Parse error.

If the current node is a script element, mark the script element as "already executed".

Pop the current node off the stack of open elements.

Switch the insertion mode to the original insertion mode and reprocess the current token.

An end tag whose tag name is "script"

Let script be the current node (which will be a script element).

Pop the current node off the stack of open elements.

Switch the insertion mode to the original insertion mode.

Let the old insertion point have the same value as the current insertion point. Let the insertion point be just before the next input character.

Increment the parser's script nesting level by one.

Run the script. This might cause some script to execute, which might cause new characters to be inserted into the tokenizer, and might cause the tokenizer to output more tokens, resulting in a reentrant invocation of the parser.

Decrement the parser's script nesting level by one. If the parser's script nesting level is zero, then set the parser pause flag to false.

Let the insertion point have the value of the old insertion point. (In other words, restore the insertion point to its previous value. This value might be the "undefined" value.)

At this stage, if there is a pending external script, then:

If the tree construction stage is being called reentrantly, say from a call to document.write():

Set the parser pause flag to true, and abort the processing of any nested invocations of the tokenizer, yielding control back to the caller. (Tokenization will resume when the caller returns to the "outer" tree construction stage.)

Otherwise:

Follow these steps:

  1. Let the script be the pending external script. There is no longer a pending external script.

  2. Pause until the script has completed loading.

  3. Let the insertion point be just before the next input character.

  4. Increment the parser's script nesting level by one (it should be zero before this step, so this sets it to one).

  5. Execute the script.

  6. Decrement the parser's script nesting level by one. If the parser's script nesting level is zero (which it always should be at this point), then set the parser pause flag to false.

  7. Let the insertion point be undefined again.

  8. If there is once again a pending external script, then repeat these steps from step 1.

Any other end tag

Pop the current node off the stack of open elements.

Switch the insertion mode to the original insertion mode.

8.2.5.12 The "in table" insertion mode

When the insertion mode is "in table", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

If the current table is tainted, then act as described in the "anything else" entry below.

Otherwise, insert the character into the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "caption"

Clear the stack back to a table context. (See below.)

Insert a marker at the end of the list of active formatting elements.

Insert an HTML element for the token, then switch the insertion mode to "in caption".

A start tag whose tag name is "colgroup"

Clear the stack back to a table context. (See below.)

Insert an HTML element for the token, then switch the insertion mode to "in column group".

A start tag whose tag name is "col"

Act as if a start tag token with the tag name "colgroup" had been seen, then reprocess the current token.

A start tag whose tag name is one of: "tbody", "tfoot", "thead"

Clear the stack back to a table context. (See below.)

Insert an HTML element for the token, then switch the insertion mode to "in table body".

A start tag whose tag name is one of: "td", "th", "tr"

Act as if a start tag token with the tag name "tbody" had been seen, then reprocess the current token.

A start tag whose tag name is "table"

Parse error. Act as if an end tag token with the tag name "table" had been seen, then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

An end tag whose tag name is "table"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token. (fragment case)

Otherwise:

Pop elements from this stack until a table element has been popped from the stack.

Reset the insertion mode appropriately.

An end tag whose tag name is one of: "body", "caption", "col", "colgroup", "html", "tbody", "td", "tfoot", "th", "thead", "tr"

Parse error. Ignore the token.

A start tag whose tag name is one of: "style", "script"

Process the token using the rules for the "in head" insertion mode.

A start tag whose tag name is "input"

If the token does not have an attribute with the name "type", or if it does, but that attribute's value is not an ASCII case-insensitive match for the string "hidden", then: act as described in the "anything else" entry below.

Otherwise:

Parse error.

Insert an HTML element for the token.

Pop that input element off the stack of open elements.

An end-of-file token

If the current node is not the root html element, then this is a parse error.

It can only be the current node in the fragment case.

Stop parsing.

Anything else

Parse error. Process the token using the rules for the "in body" insertion mode, except that if the current node is a table, tbody, tfoot, thead, or tr element, then, whenever a node would be inserted into the current node, it must instead be foster parented.

When the steps above require the UA to clear the stack back to a table context, it means that the UA must, while the current node is not a table element or an html element, pop elements from the stack of open elements.

The current node being an html element after this process is a fragment case.

8.2.5.13 The "in caption" insertion mode

When the insertion mode is "in caption", tokens must be handled as follows:

An end tag whose tag name is "caption"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token. (fragment case)

Otherwise:

Generate implied end tags.

Now, if the current node is not a caption element, then this is a parse error.

Pop elements from this stack until a caption element has been popped from the stack.

Clear the list of active formatting elements up to the last marker.

Switch the insertion mode to "in table".

A start tag whose tag name is one of: "caption", "col", "colgroup", "tbody", "td", "tfoot", "th", "thead", "tr"
An end tag whose tag name is "table"

Parse error. Act as if an end tag with the tag name "caption" had been seen, then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

An end tag whose tag name is one of: "body", "col", "colgroup", "html", "tbody", "td", "tfoot", "th", "thead", "tr"

Parse error. Ignore the token.

Anything else

Process the token using the rules for the "in body" insertion mode.

8.2.5.14 The "in column group" insertion mode

When the insertion mode is "in column group", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Insert the character into the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

A start tag whose tag name is "col"

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

Acknowledge the token's self-closing flag, if it is set.

An end tag whose tag name is "colgroup"

If the current node is the root html element, then this is a parse error; ignore the token. (fragment case)

Otherwise, pop the current node (which will be a colgroup element) from the stack of open elements. Switch the insertion mode to "in table".

An end tag whose tag name is "col"

Parse error. Ignore the token.

An end-of-file token

If the current node is the root html element, then stop parsing. (fragment case)

Otherwise, act as described in the "anything else" entry below.

Anything else

Act as if an end tag with the tag name "colgroup" had been seen, and then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

8.2.5.15 The "in table body" insertion mode

When the insertion mode is "in table body", tokens must be handled as follows:

A start tag whose tag name is "tr"

Clear the stack back to a table body context. (See below.)

Insert an HTML element for the token, then switch the insertion mode to "in row".

A start tag whose tag name is one of: "th", "td"

Parse error. Act as if a start tag with the tag name "tr" had been seen, then reprocess the current token.

An end tag whose tag name is one of: "tbody", "tfoot", "thead"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token.

Otherwise:

Clear the stack back to a table body context. (See below.)

Pop the current node from the stack of open elements. Switch the insertion mode to "in table".

A start tag whose tag name is one of: "caption", "col", "colgroup", "tbody", "tfoot", "thead"
An end tag whose tag name is "table"

If the stack of open elements does not have a tbody, thead, or tfoot element in table scope, this is a parse error. Ignore the token. (fragment case)

Otherwise:

Clear the stack back to a table body context. (See below.)

Act as if an end tag with the same tag name as the current node ("tbody", "tfoot", or "thead") had been seen, then reprocess the current token.

An end tag whose tag name is one of: "body", "caption", "col", "colgroup", "html", "td", "th", "tr"

Parse error. Ignore the token.

Anything else

Process the token using the rules for the "in table" insertion mode.

When the steps above require the UA to clear the stack back to a table body context, it means that the UA must, while the current node is not a tbody, tfoot, thead, or html element, pop elements from the stack of open elements.

The current node being an html element after this process is a fragment case.

8.2.5.16 The "in row" insertion mode

When the insertion mode is "in row", tokens must be handled as follows:

A start tag whose tag name is one of: "th", "td"

Clear the stack back to a table row context. (See below.)

Insert an HTML element for the token, then switch the insertion mode to "in cell".

Insert a marker at the end of the list of active formatting elements.

An end tag whose tag name is "tr"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token. (fragment case)

Otherwise:

Clear the stack back to a table row context. (See below.)

Pop the current node (which will be a tr element) from the stack of open elements. Switch the insertion mode to "in table body".

A start tag whose tag name is one of: "caption", "col", "colgroup", "tbody", "tfoot", "thead", "tr"
An end tag whose tag name is "table"

Act as if an end tag with the tag name "tr" had been seen, then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

An end tag whose tag name is one of: "tbody", "tfoot", "thead"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token.

Otherwise, act as if an end tag with the tag name "tr" had been seen, then reprocess the current token.

An end tag whose tag name is one of: "body", "caption", "col", "colgroup", "html", "td", "th"

Parse error. Ignore the token.

Anything else

Process the token using the rules for the "in table" insertion mode.

When the steps above require the UA to clear the stack back to a table row context, it means that the UA must, while the current node is not a tr element or an html element, pop elements from the stack of open elements.

The current node being an html element after this process is a fragment case.

8.2.5.17 The "in cell" insertion mode

When the insertion mode is "in cell", tokens must be handled as follows:

An end tag whose tag name is one of: "td", "th"

If the stack of open elements does not have an element in table scope with the same tag name as that of the token, then this is a parse error and the token must be ignored.

Otherwise:

Generate implied end tags.

Now, if the current node is not an element with the same tag name as the token, then this is a parse error.

Pop elements from this stack until an element with the same tag name as the token has been popped from the stack.

Clear the list of active formatting elements up to the last marker.

Switch the insertion mode to "in row". (The current node will be a tr element at this point.)

A start tag whose tag name is one of: "caption", "col", "colgroup", "tbody", "td", "tfoot", "th", "thead", "tr"

If the stack of open elements does not have a td or th element in table scope, then this is a parse error; ignore the token. (fragment case)

Otherwise, close the cell (see below) and reprocess the current token.

An end tag whose tag name is one of: "body", "caption", "col", "colgroup", "html"

Parse error. Ignore the token.

An end tag whose tag name is one of: "table", "tbody", "tfoot", "thead", "tr"

If the stack of open elements does not have an element in table scope with the same tag name as that of the token (which can only happen for "tbody", "tfoot" and "thead", or, in the fragment case), then this is a parse error and the token must be ignored.

Otherwise, close the cell (see below) and reprocess the current token.

Anything else

Process the token using the rules for the "in body" insertion mode.

Where the steps above say to close the cell, they mean to run the following algorithm:

  1. If the stack of open elements has a td element in table scope, then act as if an end tag token with the tag name "td" had been seen.

  2. Otherwise, the stack of open elements will have a th element in table scope; act as if an end tag token with the tag name "th" had been seen.

The stack of open elements cannot have both a td and a th element in table scope at the same time, nor can it have neither when the insertion mode is "in cell".

8.2.5.18 The "in select" insertion mode

When the insertion mode is "in select", tokens must be handled as follows:

A character token

Insert the token's character into the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

A start tag whose tag name is "option"

If the current node is an option element, act as if an end tag with the tag name "option" had been seen.

Insert an HTML element for the token.

A start tag whose tag name is "optgroup"

If the current node is an option element, act as if an end tag with the tag name "option" had been seen.

If the current node is an optgroup element, act as if an end tag with the tag name "optgroup" had been seen.

Insert an HTML element for the token.

An end tag whose tag name is "optgroup"

First, if the current node is an option element, and the node immediately before it in the stack of open elements is an optgroup element, then act as if an end tag with the tag name "option" had been seen.

If the current node is an optgroup element, then pop that node from the stack of open elements. Otherwise, this is a parse error; ignore the token.

An end tag whose tag name is "option"

If the current node is an option element, then pop that node from the stack of open elements. Otherwise, this is a parse error; ignore the token.

An end tag whose tag name is "select"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token. (fragment case)

Otherwise:

Pop elements from the stack of open elements until a select element has been popped from the stack.

Reset the insertion mode appropriately.

A start tag whose tag name is "select"

Parse error. Act as if the token had been an end tag with the tag name "select" instead.

A start tag whose tag name is one of: "input", "textarea"

Parse error. Act as if an end tag with the tag name "select" had been seen, and reprocess the token.

A start tag token whose tag name is "script"

Process the token using the rules for the "in head" insertion mode.

An end-of-file token

If the current node is not the root html element, then this is a parse error.

It can only be the current node in the fragment case.

Stop parsing.

Anything else

Parse error. Ignore the token.

8.2.5.19 The "in select in table" insertion mode

When the insertion mode is "in select in table", tokens must be handled as follows:

A start tag whose tag name is one of: "caption", "table", "tbody", "tfoot", "thead", "tr", "td", "th"

Parse error. Act as if an end tag with the tag name "select" had been seen, and reprocess the token.

An end tag whose tag name is one of: "caption", "table", "tbody", "tfoot", "thead", "tr", "td", "th"

Parse error.

If the stack of open elements has an element in table scope with the same tag name as that of the token, then act as if an end tag with the tag name "select" had been seen, and reprocess the token. Otherwise, ignore the token.

Anything else

Process the token using the rules for the "in select" insertion mode.

8.2.5.20 The "in foreign content" insertion mode

When the insertion mode is "in foreign content", tokens must be handled as follows:

A character token

Insert the token's character into the current node.

If the token is not one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE, then set the frameset-ok flag to "not ok".

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

An end tag whose tag name is "script", if the current node is a script element in the SVG namespace.

Pop the current node off the stack of open elements.

Let the old insertion point have the same value as the current insertion point. Let the insertion point be just before the next input character.

Increment the parser's script nesting level by one. Set the parser pause flag to true.

Process the script element according to the SVG rules. [SVG]

Even if this causes new characters to be inserted into the tokenizer, the parser will not be executed reentrantly, since the parser pause flag is true.

Decrement the parser's script nesting level by one. If the parser's script nesting level is zero, then set the parser pause flag to false.

Let the insertion point have the value of the old insertion point. (In other words, restore the insertion point to its previous value. This value might be the "undefined" value.)

A start tag whose tag name is neither "mglyph" nor "malignmark", if the current node is an mi element in the MathML namespace.
A start tag whose tag name is neither "mglyph" nor "malignmark", if the current node is an mo element in the MathML namespace.
A start tag whose tag name is neither "mglyph" nor "malignmark", if the current node is an mn element in the MathML namespace.
A start tag whose tag name is neither "mglyph" nor "malignmark", if the current node is an ms element in the MathML namespace.
A start tag whose tag name is neither "mglyph" nor "malignmark", if the current node is an mtext element in the MathML namespace.
A start tag whose tag name is "svg", if the current node is an annotation-xml element in the MathML namespace.
A start tag, if the current node is a foreignObject element in the SVG namespace.
A start tag, if the current node is a desc element in the SVG namespace.
A start tag, if the current node is a title element in the SVG namespace.
A start tag, if the current node is an element in the HTML namespace.
An end tag

Process the token using the rules for the secondary insertion mode.

If, after doing so, the insertion mode is still "in foreign content", but there is no element in scope that has a namespace other than the HTML namespace, switch the insertion mode to the secondary insertion mode.

A start tag whose tag name is one of: "b", "big", "blockquote", "body", "br", "center", "code", "dd", "div", "dl", "dt", "em", "embed", "h1", "h2", "h3", "h4", "h5", "h6", "head", "hr", "i", "img", "li", "listing", "menu", "meta", "nobr", "ol", "p", "pre", "ruby", "s", "small", "span", "strong", "strike", "sub", "sup", "table", "tt", "u", "ul", "var"
A start tag whose tag name is "font", if the token has any attributes named "color", "face", or "size"
An end-of-file token

Parse error.

Pop elements from the stack of open elements until the current node is in the HTML namespace.

Switch the insertion mode to the secondary insertion mode, and reprocess the token.

Any other start tag

If the current node is an element in the MathML namespace, adjust MathML attributes for the token. (This fixes the case of MathML attributes that are not all lowercase.)

If the current node is an element in the SVG namespace, and the token's tag name is one of the ones in the first column of the following table, change the tag name to the name given in the corresponding cell in the second column. (This fixes the case of SVG elements that are not all lowercase.)

Tag name Element name
altglyph altGlyph
altglyphdef altGlyphDef
altglyphitem altGlyphItem
animatecolor animateColor
animatemotion animateMotion
animatetransform animateTransform
clippath clipPath
feblend feBlend
fecolormatrix feColorMatrix
fecomponenttransfer feComponentTransfer
fecomposite feComposite
feconvolvematrix feConvolveMatrix
fediffuselighting feDiffuseLighting
fedisplacementmap feDisplacementMap
fedistantlight feDistantLight
feflood feFlood
fefunca feFuncA
fefuncb feFuncB
fefuncg feFuncG
fefuncr feFuncR
fegaussianblur feGaussianBlur
feimage feImage
femerge feMerge
femergenode feMergeNode
femorphology feMorphology
feoffset feOffset
fepointlight fePointLight
fespecularlighting feSpecularLighting
fespotlight feSpotLight
fetile feTile
feturbulence feTurbulence
foreignobject foreignObject
glyphref glyphRef
lineargradient linearGradient
radialgradient radialGradient
textpath textPath

If the current node is an element in the SVG namespace, adjust SVG attributes for the token. (This fixes the case of SVG attributes that are not all lowercase.)

Adjust foreign attributes for the token. (This fixes the use of namespaced attributes, in particular XLink in SVG.)

Insert a foreign element for the token, in the same namespace as the current node.

If the token has its self-closing flag set, pop the current node off the stack of open elements and acknowledge the token's self-closing flag.

8.2.5.21 The "after body" insertion mode

When the insertion mode is "after body", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Process the token using the rules for the "in body" insertion mode.

A comment token

Append a Comment node to the first element in the stack of open elements (the html element), with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

An end tag whose tag name is "html"

If the parser was originally created as part of the HTML fragment parsing algorithm, this is a parse error; ignore the token. (fragment case)

Otherwise, switch the insertion mode to "after after body".

An end-of-file token

Stop parsing.

Anything else

Parse error. Switch the insertion mode to "in body" and reprocess the token.

8.2.5.22 The "in frameset" insertion mode

When the insertion mode is "in frameset", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Insert the character into the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

A start tag whose tag name is "frameset"

Insert an HTML element for the token.

An end tag whose tag name is "frameset"

If the current node is the root html element, then this is a parse error; ignore the token. (fragment case)

Otherwise, pop the current node from the stack of open elements.

If the parser was not originally created as part of the HTML fragment parsing algorithm (fragment case), and the current node is no longer a frameset element, then switch the insertion mode to "after frameset".

A start tag whose tag name is "frame"

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

Acknowledge the token's self-closing flag, if it is set.

A start tag whose tag name is "noframes"

Process the token using the rules for the "in head" insertion mode.

An end-of-file token

If the current node is not the root html element, then this is a parse error.

It can only be the current node in the fragment case.

Stop parsing.

Anything else

Parse error. Ignore the token.

8.2.5.23 The "after frameset" insertion mode

When the insertion mode is "after frameset", tokens must be handled as follows:

A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE

Insert the character into the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

An end tag whose tag name is "html"

Switch the insertion mode to "after after frameset".

A start tag whose tag name is "noframes"

Process the token using the rules for the "in head" insertion mode.

An end-of-file token

Stop parsing.

Anything else

Parse error. Ignore the token.

This doesn't handle UAs that don't support frames, or that do support frames but want to show the NOFRAMES content. Supporting the former is easy; supporting the latter is harder.

8.2.5.24 The "after after body" insertion mode

When the insertion mode is "after after body", tokens must be handled as follows:

A comment token

Append a Comment node to the Document object with the data attribute set to the data given in the comment token.

A DOCTYPE token
A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE
A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

An end-of-file token

Stop parsing.

Anything else

Parse error. Switch the insertion mode to "in body" and reprocess the token.

8.2.5.25 The "after after frameset" insertion mode

When the insertion mode is "after after frameset", tokens must be handled as follows:

A comment token

Append a Comment node to the Document object with the data attribute set to the data given in the comment token.

A DOCTYPE token
A character token that is one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), or U+0020 SPACE
A start tag whose tag name is "html"

Process the token using the rules for the "in body" insertion mode.

An end-of-file token

Stop parsing.

A start tag whose tag name is "noframes"

Process the token using the rules for the "in head" insertion mode.

Anything else

Parse error. Ignore the token.

8.2.6 The end

Once the user agent stops parsing the document, the user agent must follow the steps in this section.

First, the current document readiness must be set to "interactive".

Then, the rules for when a script completes loading start applying (script execution is no longer managed by the parser).

If any of the scripts in the list of scripts that will execute as soon as possible have completed loading, or if the list of scripts that will execute asynchronously is not empty and the first script in that list has completed loading, then the user agent must act as if those scripts just completed loading, following the rules given for that in the script element definition.

Then, if the list of scripts that will execute when the document has finished parsing is not empty, and the first item in this list has already completed loading, then the user agent must act as if that script just finished loading.

By this point, there will be no scripts that have loaded but have not yet been executed.

The user agent must then fire a simple event called DOMContentLoaded at the Document.

Once everything that delays the load event of the document has completed, the user agent must run the following steps:

  1. Queue a task to set the current document readiness to "complete".
  2. If the Document is in a browsing context, then queue a task to fire a simple event called load at the Document's Window object, but with its target set to the Document object (and the currentTarget set to the Window object).
  3. If the Document has a pending state object, then queue a task to fire a popstate event in no namespace on the Document's Window object using the PopStateEvent interface, with the state attribute set to the current value of the pending state object. This event must bubble but not be cancelable and has no default action.

The task source for these tasks is the DOM manipulation task source.

delaying the load event for things like image loads allows for intranet port scans (even without javascript!). Should we really encode that into the spec?

8.2.7 Coercing an HTML DOM into an infoset

When an application uses an HTML parser in conjunction with an XML pipeline, it is possible that the constructed DOM is not compatible with the XML tool chain in certain subtle ways. For example, an XML toolchain might not be able to represent attributes with the name xmlns, since they conflict with the Namespaces in XML syntax. There is also some data that the HTML parser generates that isn't included in the DOM itself. This section specifies some rules for handling these issues.

If the XML API being used doesn't support DOCTYPEs, the tool may drop DOCTYPEs altogether.

If the XML API doesn't support attributes in no namespace that are named "xmlns", attributes whose names start with "xmlns:", or attributes in the XMLNS namespace, then the tool may drop such attributes.

The tool may annotate the output with any namespace declarations required for proper operation.

If the XML API being used restricts the allowable characters in the local names of elements and attributes, then the tool may map all element and attribute local names that the API wouldn't support to a set of names that are allowed, by replacing any character that isn't supported with the uppercase letter U and the six digits of the character's Unicode code point when expressed in hexadecimal, using digits 0-9 and capital letters A-F as the symbols, in increasing numeric order.

For example, the element name foo<bar, which can be output by the HTML parser, though it is neither a legal HTML element name nor a well-formed XML element name, would be converted into fooU00003Cbar, which is a well-formed XML element name (though it's still not legal in HTML by any means).

As another example, consider the attribute xlink:href. Used on a MathML element, it becomes, after being adjusted, an attribute with a prefix "xlink" and a local name "href". However, used on an HTML element, it becomes an attribute with no prefix and the local name "xlink:href", which is not a valid NCName, and thus might not be accepted by an XML API. It could thus get converted, becoming "xlinkU00003Ahref".

The resulting names from this conversion conveniently can't clash with any attribute generated by the HTML parser, since those are all either lowercase or those listed in the adjust foreign attributes algorithm's table.

If the XML API restricts comments from having two consecutive U+002D HYPHEN-MINUS characters (--), the tool may insert a single U+0020 SPACE character between any such offending characters.

If the XML API restricts comments from ending in a U+002D HYPHEN-MINUS character (-), the tool may insert a single U+0020 SPACE character at the end of such comments.

If the XML API restricts allowed characters in character data, the tool may replace any U+000C FORM FEED (FF) character with a U+0020 SPACE character, and any other literal non-XML character with a U+FFFD REPLACEMENT CHARACTER.

If the tool has no way to convey out-of-band information, then the tool may drop the following information:

The mutations allowed by this section apply after the HTML parser's rules have been applied. For example, a <a::> start tag will be closed by a </a::> end tag, and never by a </aU00003AU00003A> end tag, even if the user agent is using the rules above to then generate an actual element in the DOM with the name aU00003AU00003A for that start tag.

8.3 Namespaces

The HTML namespace is: http://www.w3.org/1999/xhtml

The MathML namespace is: http://www.w3.org/1998/Math/MathML

The SVG namespace is: http://www.w3.org/2000/svg

The XLink namespace is: http://www.w3.org/1999/xlink

The XML namespace is: http://www.w3.org/XML/1998/namespace

The XMLNS namespace is: http://www.w3.org/2000/xmlns/


Data mining tools and other user agents that perform operations on text/html content without running scripts, evaluating CSS or XPath expressions, or otherwise exposing the resulting DOM to arbitrary content, may "support namespaces" by just asserting that their DOM node analogues are in certain namespaces, without actually exposing the above strings.

8.4 Serializing HTML fragments

The following steps form the HTML fragment serialization algorithm. The algorithm takes as input a DOM Element or Document, referred to as the node, and either returns a string or raises an exception.

This algorithm serializes the children of the node being serialized, not the node itself.

  1. Let s be a string, and initialize it to the empty string.

  2. For each child node of the node, in tree order, run the following steps:

    1. Let current node be the child node being processed.

    2. Append the appropriate string from the following list to s:

      If current node is an Element

      Append a U+003C LESS-THAN SIGN (<) character, followed by the element's tag name. (For nodes created by the HTML parser or Document.createElement(), the tag name will be lowercase.)

      For each attribute that the element has, append a U+0020 SPACE character, the attribute's name (which, for attributes set by the HTML parser or by Element.setAttributeNode() or Element.setAttribute(), will be lowercase), a U+003D EQUALS SIGN (=) character, a U+0022 QUOTATION MARK (") character, the attribute's value, escaped as described below in attribute mode, and a second U+0022 QUOTATION MARK (") character.

      While the exact order of attributes is UA-defined, and may depend on factors such as the order that the attributes were given in the original markup, the sort order must be stable, such that consecutive invocations of this algorithm serialize an element's attributes in the same order.

      Append a U+003E GREATER-THAN SIGN (>) character.

      If current node is an area, base, basefont, bgsound, br, col, embed, frame, hr, img, input, keygen, link, meta, param, spacer, or wbr element, then continue on to the next child node at this point.

      If current node is a pre, textarea, or listing element, append a U+000A LINE FEED (LF) character.

      Append the value of running the HTML fragment serialization algorithm on the current node element (thus recursing into this algorithm for that element), followed by a U+003C LESS-THAN SIGN (<) character, a U+002F SOLIDUS (/) character, the element's tag name again, and finally a U+003E GREATER-THAN SIGN (>) character.

      If current node is a Text or CDATASection node

      If one of the ancestors of current node is a style, script, xmp, iframe, noembed, noframes, noscript, or plaintext element, then append the value of current node's data DOM attribute literally.

      Otherwise, append the value of current node's data DOM attribute, escaped as described below.

      If current node is a Comment

      Append the literal string <!-- (U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS), followed by the value of current node's data DOM attribute, followed by the literal string --> (U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN).

      If current node is a ProcessingInstruction

      Append the literal string <? (U+003C LESS-THAN SIGN, U+003F QUESTION MARK), followed by the value of current node's target DOM attribute, followed by a single U+0020 SPACE character, followed by the value of current node's data DOM attribute, followed by a single U+003E GREATER-THAN SIGN character ('>').

      If current node is a DocumentType

      Append the literal string <!DOCTYPE (U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+0044 LATIN CAPITAL LETTER D, U+004F LATIN CAPITAL LETTER O, U+0043 LATIN CAPITAL LETTER C, U+0054 LATIN CAPITAL LETTER T, U+0059 LATIN CAPITAL LETTER Y, U+0050 LATIN CAPITAL LETTER P, U+0045 LATIN CAPITAL LETTER E), followed by a space (U+0020 SPACE), followed by the value of current node's name DOM attribute, followed by the literal string > (U+003E GREATER-THAN SIGN).

      Other node types (e.g. Attr) cannot occur as children of elements. If, despite this, they somehow do occur, this algorithm must raise an INVALID_STATE_ERR exception.

  3. The result of the algorithm is the string s.

Escaping a string (for the purposes of the algorithm above) consists of replacing any occurrences of the "&" character by the string "&amp;", any occurrences of the U+00A0 NO-BREAK SPACE character by the string "&nbsp;", and, if the algorithm was invoked in the attribute mode, any occurrences of the """ character by the string "&quot;", or if it was not, any occurrences of the "<" character by the string "&lt;", any occurrences of the ">" character by the string "&gt;".

Entity reference nodes are assumed to be expanded by the user agent, and are therefore not covered in the algorithm above.

It is possible that the output of this algorithm, if parsed with an HTML parser, will not return the original tree structure. For instance, if a textarea element to which a Comment node has been appended is serialized and the output is then reparsed, the comment will end up being displayed in the text field. Similarly, if, as a result of DOM manipulation, an element contains a comment that contains the literal string "-->", then when the result of serializing the element is parsed, the comment will be truncated at that point and the rest of the comment will be interpreted as markup. More examples would be making a script element contain a text node with the text string "</script>", or having a p element that contains a ul element (as the ul element's start tag would imply the end tag for the p).

8.5 Parsing HTML fragments

The following steps form the HTML fragment parsing algorithm. The algorithm optionally takes as input an Element node, referred to as the context element, which gives the context for the parser, as well as input, a string to parse, and returns a list of zero or more nodes.

Parts marked fragment case in algorithms in the parser section are parts that only occur if the parser was created for the purposes of this algorithm (and with a context element). The algorithms have been annotated with such markings for informational purposes only; such markings have no normative weight. If it is possible for a condition described as a fragment case to occur even when the parser wasn't created for the purposes of handling this algorithm, then that is an error in the specification.

  1. Create a new Document node, and mark it as being an HTML document.

  2. If there is a context element, and the Document of the context element is in quirks mode, then let the Document be in quirks mode. Otherwise, if there is a context element, and the Document of the context element is in limited quirks mode, then let the Document be in limited quirks mode. Otherwise, leave the Document in no quirks mode.

  3. Create a new HTML parser, and associate it with the just created Document node.

  4. If there is a context element, run these substeps:

    1. Set the HTML parser's tokenization stage's content model flag according to the context element, as follows:

      If it is a title or textarea element
      Set the content model flag to the RCDATA state.
      If it is a style, script, xmp, iframe, noembed, or noframes element
      Set the content model flag to the CDATA state.
      If it is a noscript element
      If the scripting flag is enabled, set the content model flag to the CDATA state. Otherwise, set the content model flag to the PCDATA state.
      If it is a plaintext element
      Set the content model flag to PLAINTEXT.
      Otherwise
      Leave the content model flag in the PCDATA state.
    2. Let root be a new html element with no attributes.

    3. Append the element root to the Document node created above.

    4. Set up the parser's stack of open elements so that it contains just the single element root.

    5. Reset the parser's insertion mode appropriately.

      The parser will reference the context element as part of that algorithm.

    6. Set the parser's form element pointer to the nearest node to the context element that is a form element (going straight up the ancestor chain, and including the element itself, if it is a form element), or, if there is no such form element, to null.

  5. Place into the input stream for the HTML parser just created the input. The encoding confidence is irrelevant.

  6. Start the parser and let it run until it has consumed all the characters just inserted into the input stream.

  7. If there is a context element, return the child nodes of root, in tree order.

    Otherwise, return the children of the Document object, in tree order.

8.6 Named character references

This table lists the character reference names that are supported by HTML, and the code points to which they refer. It is referenced by the previous sections.

Name Character
AElig; U+000C6
AElig U+000C6
AMP; U+00026
AMP U+00026
Aacute; U+000C1
Aacute U+000C1
Abreve; U+00102
Acirc; U+000C2
Acirc U+000C2
Acy; U+00410
Afr; U+1D504
Agrave; U+000C0
Agrave U+000C0
Alpha; U+00391
Amacr; U+00100
And; U+02A53
Aogon; U+00104
Aopf; U+1D538
ApplyFunction; U+02061
Aring; U+000C5
Aring U+000C5
Ascr; U+1D49C
Assign; U+02254
Atilde; U+000C3
Atilde U+000C3
Auml; U+000C4
Auml U+000C4
Backslash; U+02216
Barv; U+02AE7
Barwed; U+02306
Bcy; U+00411
Because; U+02235
Bernoullis; U+0212C
Beta; U+00392
Bfr; U+1D505
Bopf; U+1D539
Breve; U+002D8
Bscr; U+0212C
Bumpeq; U+0224E
CHcy; U+00427
COPY; U+000A9
COPY U+000A9
Cacute; U+00106
Cap; U+022D2
CapitalDifferentialD; U+02145
Cayleys; U+0212D
Ccaron; U+0010C
Ccedil; U+000C7
Ccedil U+000C7
Ccirc; U+00108
Cconint; U+02230
Cdot; U+0010A
Cedilla; U+000B8
CenterDot; U+000B7
Cfr; U+0212D
Chi; U+003A7
CircleDot; U+02299
CircleMinus; U+02296
CirclePlus; U+02295
CircleTimes; U+02297
ClockwiseContourIntegral; U+02232
CloseCurlyDoubleQuote; U+0201D
CloseCurlyQuote; U+02019
Colon; U+02237
Colone; U+02A74
Congruent; U+02261
Conint; U+0222F
ContourIntegral; U+0222E
Copf; U+02102
Coproduct; U+02210
CounterClockwiseContourIntegral; U+02233
Cross; U+02A2F
Cscr; U+1D49E
Cup; U+022D3
CupCap; U+0224D
DD; U+02145
DDotrahd; U+02911
DJcy; U+00402
DScy; U+00405
DZcy; U+0040F
Dagger; U+02021
Darr; U+021A1
Dashv; U+02AE4
Dcaron; U+0010E
Dcy; U+00414
Del; U+02207
Delta; U+00394
Dfr; U+1D507
DiacriticalAcute; U+000B4
DiacriticalDot; U+002D9
DiacriticalDoubleAcute; U+002DD
DiacriticalGrave; U+00060
DiacriticalTilde; U+002DC
Diamond; U+022C4
DifferentialD; U+02146
Dopf; U+1D53B
Dot; U+000A8
DotDot; U+020DC
DotEqual; U+02250
DoubleContourIntegral; U+0222F
DoubleDot; U+000A8
DoubleDownArrow; U+021D3
DoubleLeftArrow; U+021D0
DoubleLeftRightArrow; U+021D4
DoubleLeftTee; U+02AE4
DoubleLongLeftArrow; U+027F8
DoubleLongLeftRightArrow; U+027FA
DoubleLongRightArrow; U+027F9
DoubleRightArrow; U+021D2
DoubleRightTee; U+022A8
DoubleUpArrow; U+021D1
DoubleUpDownArrow; U+021D5
DoubleVerticalBar; U+02225
DownArrow; U+02193
DownArrowBar; U+02913
DownArrowUpArrow; U+021F5
DownBreve; U+00311
DownLeftRightVector; U+02950
DownLeftTeeVector; U+0295E
DownLeftVector; U+021BD
DownLeftVectorBar; U+02956
DownRightTeeVector; U+0295F
DownRightVector; U+021C1
DownRightVectorBar; U+02957
DownTee; U+022A4
DownTeeArrow; U+021A7
Downarrow; U+021D3
Dscr; U+1D49F
Dstrok; U+00110
ENG; U+0014A
ETH; U+000D0
ETH U+000D0
Eacute; U+000C9
Eacute U+000C9
Ecaron; U+0011A
Ecirc; U+000CA
Ecirc U+000CA
Ecy; U+0042D
Edot; U+00116
Efr; U+1D508
Egrave; U+000C8
Egrave U+000C8
Element; U+02208
Emacr; U+00112
EmptySmallSquare; U+025FB
EmptyVerySmallSquare; U+025AB
Eogon; U+00118
Eopf; U+1D53C
Epsilon; U+00395
Equal; U+02A75
EqualTilde; U+02242
Equilibrium; U+021CC
Escr; U+02130
Esim; U+02A73
Eta; U+00397
Euml; U+000CB
Euml U+000CB
Exists; U+02203
ExponentialE; U+02147
Fcy; U+00424
Ffr; U+1D509
FilledSmallSquare; U+025FC
FilledVerySmallSquare; U+025AA
Fopf; U+1D53D
ForAll; U+02200
Fouriertrf; U+02131
Fscr; U+02131
GJcy; U+00403
GT; U+0003E
GT U+0003E
Gamma; U+00393
Gammad; U+003DC
Gbreve; U+0011E
Gcedil; U+00122
Gcirc; U+0011C
Gcy; U+00413
Gdot; U+00120
Gfr; U+1D50A
Gg; U+022D9
Gopf; U+1D53E
GreaterEqual; U+02265
GreaterEqualLess; U+022DB
GreaterFullEqual; U+02267
GreaterGreater; U+02AA2
GreaterLess; U+02277
GreaterSlantEqual; U+02A7E
GreaterTilde; U+02273
Gscr; U+1D4A2
Gt; U+0226B
HARDcy; U+0042A
Hacek; U+002C7
Hat; U+0005E
Hcirc; U+00124
Hfr; U+0210C
HilbertSpace; U+0210B
Hopf; U+0210D
HorizontalLine; U+02500
Hscr; U+0210B
Hstrok; U+00126
HumpDownHump; U+0224E
HumpEqual; U+0224F
IEcy; U+00415
IJlig; U+00132
IOcy; U+00401
Iacute; U+000CD
Iacute U+000CD
Icirc; U+000CE
Icirc U+000CE
Icy; U+00418
Idot; U+00130
Ifr; U+02111
Igrave; U+000CC
Igrave U+000CC
Im; U+02111
Imacr; U+0012A
ImaginaryI; U+02148
Implies; U+021D2
Int; U+0222C
Integral; U+0222B
Intersection; U+022C2
InvisibleComma; U+02063
InvisibleTimes; U+02062
Iogon; U+0012E
Iopf; U+1D540
Iota; U+00399
Iscr; U+02110
Itilde; U+00128
Iukcy; U+00406
Iuml; U+000CF
Iuml U+000CF
Jcirc; U+00134
Jcy; U+00419
Jfr; U+1D50D
Jopf; U+1D541
Jscr; U+1D4A5
Jsercy; U+00408
Jukcy; U+00404
KHcy; U+00425
KJcy; U+0040C
Kappa; U+0039A
Kcedil; U+00136
Kcy; U+0041A
Kfr; U+1D50E
Kopf; U+1D542
Kscr; U+1D4A6
LJcy; U+00409
LT; U+0003C
LT U+0003C
Lacute; U+00139
Lambda; U+0039B
Lang; U+027EA
Laplacetrf; U+02112
Larr; U+0219E
Lcaron; U+0013D
Lcedil; U+0013B
Lcy; U+0041B
LeftAngleBracket; U+027E8
LeftArrow; U+02190
LeftArrowBar; U+021E4
LeftArrowRightArrow; U+021C6
LeftCeiling; U+02308
LeftDoubleBracket; U+027E6
LeftDownTeeVector; U+02961
LeftDownVector; U+021C3
LeftDownVectorBar; U+02959
LeftFloor; U+0230A
LeftRightArrow; U+02194
LeftRightVector; U+0294E
LeftTee; U+022A3
LeftTeeArrow; U+021A4
LeftTeeVector; U+0295A
LeftTriangle; U+022B2
LeftTriangleBar; U+029CF
LeftTriangleEqual; U+022B4
LeftUpDownVector; U+02951
LeftUpTeeVector; U+02960
LeftUpVector; U+021BF
LeftUpVectorBar; U+02958
LeftVector; U+021BC
LeftVectorBar; U+02952
Leftarrow; U+021D0
Leftrightarrow; U+021D4
LessEqualGreater; U+022DA
LessFullEqual; U+02266
LessGreater; U+02276
LessLess; U+02AA1
LessSlantEqual; U+02A7D
LessTilde; U+02272
Lfr; U+1D50F
Ll; U+022D8
Lleftarrow; U+021DA
Lmidot; U+0013F
LongLeftArrow; U+027F5
LongLeftRightArrow; U+027F7
LongRightArrow; U+027F6
Longleftarrow; U+027F8
Longleftrightarrow; U+027FA
Longrightarrow; U+027F9
Lopf; U+1D543
LowerLeftArrow; U+02199
LowerRightArrow; U+02198
Lscr; U+02112
Lsh; U+021B0
Lstrok; U+00141
Lt; U+0226A
Map; U+02905
Mcy; U+0041C
MediumSpace; U+0205F
Mellintrf; U+02133
Mfr; U+1D510
MinusPlus; U+02213
Mopf; U+1D544
Mscr; U+02133
Mu; U+0039C
NJcy; U+0040A
Nacute; U+00143
Ncaron; U+00147
Ncedil; U+00145
Ncy; U+0041D
NegativeMediumSpace; U+0200B
NegativeThickSpace; U+0200B
NegativeThinSpace; U+0200B
NegativeVeryThinSpace; U+0200B
NestedGreaterGreater; U+0226B
NestedLessLess; U+0226A
NewLine; U+0000A
Nfr; U+1D511
NoBreak; U+02060
NonBreakingSpace; U+000A0
Nopf; U+02115
Not; U+02AEC
NotCongruent; U+02262
NotCupCap; U+0226D
NotDoubleVerticalBar; U+02226
NotElement; U+02209
NotEqual; U+02260
NotExists; U+02204
NotGreater; U+0226F
NotGreaterEqual; U+02271
NotGreaterLess; U+02279
NotGreaterTilde; U+02275
NotLeftTriangle; U+022EA
NotLeftTriangleEqual; U+022EC
NotLess; U+0226E
NotLessEqual; U+02270
NotLessGreater; U+02278
NotLessTilde; U+02274
NotPrecedes; U+02280
NotPrecedesSlantEqual; U+022E0
NotReverseElement; U+0220C
NotRightTriangle; U+022EB
NotRightTriangleEqual; U+022ED
NotSquareSubsetEqual; U+022E2
NotSquareSupersetEqual; U+022E3
NotSubsetEqual; U+02288
NotSucceeds; U+02281
NotSucceedsSlantEqual; U+022E1
NotSupersetEqual; U+02289
NotTilde; U+02241
NotTildeEqual; U+02244
NotTildeFullEqual; U+02247
NotTildeTilde; U+02249
NotVerticalBar; U+02224
Nscr; U+1D4A9
Ntilde; U+000D1
Ntilde U+000D1
Nu; U+0039D
OElig; U+00152
Oacute; U+000D3
Oacute U+000D3
Ocirc; U+000D4
Ocirc U+000D4
Ocy; U+0041E
Odblac; U+00150
Ofr; U+1D512
Ograve; U+000D2
Ograve U+000D2
Omacr; U+0014C
Omega; U+003A9
Omicron; U+0039F
Oopf; U+1D546
OpenCurlyDoubleQuote; U+0201C
OpenCurlyQuote; U+02018
Or; U+02A54
Oscr; U+1D4AA
Oslash; U+000D8
Oslash U+000D8
Otilde; U+000D5
Otilde U+000D5
Otimes; U+02A37
Ouml; U+000D6
Ouml U+000D6
OverBar; U+000AF
OverBrace; U+023DE
OverBracket; U+023B4
OverParenthesis; U+023DC
PartialD; U+02202
Pcy; U+0041F
Pfr; U+1D513
Phi; U+003A6
Pi; U+003A0
PlusMinus; U+000B1
Poincareplane; U+0210C
Popf; U+02119
Pr; U+02ABB
Precedes; U+0227A
PrecedesEqual; U+02AAF
PrecedesSlantEqual; U+0227C
PrecedesTilde; U+0227E
Prime; U+02033
Product; U+0220F
Proportion; U+02237
Proportional; U+0221D
Pscr; U+1D4AB
Psi; U+003A8
QUOT; U+00022
QUOT U+00022
Qfr; U+1D514
Qopf; U+0211A
Qscr; U+1D4AC
RBarr; U+02910
REG; U+000AE
REG U+000AE
Racute; U+00154
Rang; U+027EB
Rarr; U+021A0
Rarrtl; U+02916
Rcaron; U+00158
Rcedil; U+00156
Rcy; U+00420
Re; U+0211C
ReverseElement; U+0220B
ReverseEquilibrium; U+021CB
ReverseUpEquilibrium; U+0296F
Rfr; U+0211C
Rho; U+003A1
RightAngleBracket; U+027E9
RightArrow; U+02192
RightArrowBar; U+021E5
RightArrowLeftArrow; U+021C4
RightCeiling; U+02309
RightDoubleBracket; U+027E7
RightDownTeeVector; U+0295D
RightDownVector; U+021C2
RightDownVectorBar; U+02955
RightFloor; U+0230B
RightTee; U+022A2
RightTeeArrow; U+021A6
RightTeeVector; U+0295B
RightTriangle; U+022B3
RightTriangleBar; U+029D0
RightTriangleEqual; U+022B5
RightUpDownVector; U+0294F
RightUpTeeVector; U+0295C
RightUpVector; U+021BE
RightUpVectorBar; U+02954
RightVector; U+021C0
RightVectorBar; U+02953
Rightarrow; U+021D2
Ropf; U+0211D
RoundImplies; U+02970
Rrightarrow; U+021DB
Rscr; U+0211B
Rsh; U+021B1
RuleDelayed; U+029F4
SHCHcy; U+00429
SHcy; U+00428
SOFTcy; U+0042C
Sacute; U+0015A
Sc; U+02ABC
Scaron; U+00160
Scedil; U+0015E
Scirc; U+0015C
Scy; U+00421
Sfr; U+1D516
ShortDownArrow; U+02193
ShortLeftArrow; U+02190
ShortRightArrow; U+02192
ShortUpArrow; U+02191
Sigma; U+003A3
SmallCircle; U+02218
Sopf; U+1D54A
Sqrt; U+0221A
Square; U+025A1
SquareIntersection; U+02293
SquareSubset; U+0228F
SquareSubsetEqual; U+02291
SquareSuperset; U+02290
SquareSupersetEqual; U+02292
SquareUnion; U+02294
Sscr; U+1D4AE
Star; U+022C6
Sub; U+022D0
Subset; U+022D0
SubsetEqual; U+02286
Succeeds; U+0227B
SucceedsEqual; U+02AB0
SucceedsSlantEqual; U+0227D
SucceedsTilde; U+0227F
SuchThat; U+0220B
Sum; U+02211
Sup; U+022D1
Superset; U+02283
SupersetEqual; U+02287
Supset; U+022D1
THORN; U+000DE
THORN U+000DE
TRADE; U+02122
TSHcy; U+0040B
TScy; U+00426
Tab; U+00009
Tau; U+003A4
Tcaron; U+00164
Tcedil; U+00162
Tcy; U+00422
Tfr; U+1D517
Therefore; U+02234
Theta; U+00398
ThinSpace; U+02009
Tilde; U+0223C
TildeEqual; U+02243
TildeFullEqual; U+02245
TildeTilde; U+02248
Topf; U+1D54B
TripleDot; U+020DB
Tscr; U+1D4AF
Tstrok; U+00166
Uacute; U+000DA
Uacute U+000DA
Uarr; U+0219F
Uarrocir; U+02949
Ubrcy; U+0040E
Ubreve; U+0016C
Ucirc; U+000DB
Ucirc U+000DB
Ucy; U+00423
Udblac; U+00170
Ufr; U+1D518
Ugrave; U+000D9
Ugrave U+000D9
Umacr; U+0016A
UnderBar; U+00332
UnderBrace; U+023DF
UnderBracket; U+023B5
UnderParenthesis; U+023DD
Union; U+022C3
UnionPlus; U+0228E
Uogon; U+00172
Uopf; U+1D54C
UpArrow; U+02191
UpArrowBar; U+02912
UpArrowDownArrow; U+021C5
UpDownArrow; U+02195
UpEquilibrium; U+0296E
UpTee; U+022A5
UpTeeArrow; U+021A5
Uparrow; U+021D1
Updownarrow; U+021D5
UpperLeftArrow; U+02196
UpperRightArrow; U+02197
Upsi; U+003D2
Upsilon; U+003A5
Uring; U+0016E
Uscr; U+1D4B0
Utilde; U+00168
Uuml; U+000DC
Uuml U+000DC
VDash; U+022AB
Vbar; U+02AEB
Vcy; U+00412
Vdash; U+022A9
Vdashl; U+02AE6
Vee; U+022C1
Verbar; U+02016
Vert; U+02016
VerticalBar; U+02223
VerticalLine; U+0007C
VerticalSeparator; U+02758
VerticalTilde; U+02240
VeryThinSpace; U+0200A
Vfr; U+1D519
Vopf; U+1D54D
Vscr; U+1D4B1
Vvdash; U+022AA
Wcirc; U+00174
Wedge; U+022C0
Wfr; U+1D51A
Wopf; U+1D54E
Wscr; U+1D4B2
Xfr; U+1D51B
Xi; U+0039E
Xopf; U+1D54F
Xscr; U+1D4B3
YAcy; U+0042F
YIcy; U+00407
YUcy; U+0042E
Yacute; U+000DD
Yacute U+000DD
Ycirc; U+00176
Ycy; U+0042B
Yfr; U+1D51C
Yopf; U+1D550
Yscr; U+1D4B4
Yuml; U+00178
ZHcy; U+00416
Zacute; U+00179
Zcaron; U+0017D
Zcy; U+00417
Zdot; U+0017B
ZeroWidthSpace; U+0200B
Zeta; U+00396
Zfr; U+02128
Zopf; U+02124
Zscr; U+1D4B5
aacute; U+000E1
aacute U+000E1
abreve; U+00103
ac; U+0223E
acd; U+0223F
acirc; U+000E2
acirc U+000E2
acute; U+000B4
acute U+000B4
acy; U+00430
aelig; U+000E6
aelig U+000E6
af; U+02061
afr; U+1D51E
agrave; U+000E0
agrave U+000E0
alefsym; U+02135
aleph; U+02135
alpha; U+003B1
amacr; U+00101
amalg; U+02A3F
amp; U+00026
amp U+00026
and; U+02227
andand; U+02A55
andd; U+02A5C
andslope; U+02A58
andv; U+02A5A
ang; U+02220
ange; U+029A4
angle; U+02220
angmsd; U+02221
angmsdaa; U+029A8
angmsdab; U+029A9
angmsdac; U+029AA
angmsdad; U+029AB
angmsdae; U+029AC
angmsdaf; U+029AD
angmsdag; U+029AE
angmsdah; U+029AF
angrt; U+0221F
angrtvb; U+022BE
angrtvbd; U+0299D
angsph; U+02222
angst; U+0212B
angzarr; U+0237C
aogon; U+00105
aopf; U+1D552
ap; U+02248
apE; U+02A70
apacir; U+02A6F
ape; U+0224A
apid; U+0224B
apos; U+00027
approx; U+02248
approxeq; U+0224A
aring; U+000E5
aring U+000E5
ascr; U+1D4B6
ast; U+0002A
asymp; U+02248
asympeq; U+0224D
atilde; U+000E3
atilde U+000E3
auml; U+000E4
auml U+000E4
awconint; U+02233
awint; U+02A11
bNot; U+02AED
backcong; U+0224C
backepsilon; U+003F6
backprime; U+02035
backsim; U+0223D
backsimeq; U+022CD
barvee; U+022BD
barwed; U+02305
barwedge; U+02305
bbrk; U+023B5
bbrktbrk; U+023B6
bcong; U+0224C
bcy; U+00431
bdquo; U+0201E
becaus; U+02235
because; U+02235
bemptyv; U+029B0
bepsi; U+003F6
bernou; U+0212C
beta; U+003B2
beth; U+02136
between; U+0226C
bfr; U+1D51F
bigcap; U+022C2
bigcirc; U+025EF
bigcup; U+022C3
bigodot; U+02A00
bigoplus; U+02A01
bigotimes; U+02A02
bigsqcup; U+02A06
bigstar; U+02605
bigtriangledown; U+025BD
bigtriangleup; U+025B3
biguplus; U+02A04
bigvee; U+022C1
bigwedge; U+022C0
bkarow; U+0290D
blacklozenge; U+029EB
blacksquare; U+025AA
blacktriangle; U+025B4
blacktriangledown; U+025BE
blacktriangleleft; U+025C2
blacktriangleright; U+025B8
blank; U+02423
blk12; U+02592
blk14; U+02591
blk34; U+02593
block; U+02588
bnot; U+02310
bopf; U+1D553
bot; U+022A5
bottom; U+022A5
bowtie; U+022C8
boxDL; U+02557
boxDR; U+02554
boxDl; U+02556
boxDr; U+02553
boxH; U+02550
boxHD; U+02566
boxHU; U+02569
boxHd; U+02564
boxHu; U+02567
boxUL; U+0255D
boxUR; U+0255A
boxUl; U+0255C
boxUr; U+02559
boxV; U+02551
boxVH; U+0256C
boxVL; U+02563
boxVR; U+02560
boxVh; U+0256B
boxVl; U+02562
boxVr; U+0255F
boxbox; U+029C9
boxdL; U+02555
boxdR; U+02552
boxdl; U+02510
boxdr; U+0250C
boxh; U+02500
boxhD; U+02565
boxhU; U+02568
boxhd; U+0252C
boxhu; U+02534
boxminus; U+0229F
boxplus; U+0229E
boxtimes; U+022A0
boxuL; U+0255B
boxuR; U+02558
boxul; U+02518
boxur; U+02514
boxv; U+02502
boxvH; U+0256A
boxvL; U+02561
boxvR; U+0255E
boxvh; U+0253C
boxvl; U+02524
boxvr; U+0251C
bprime; U+02035
breve; U+002D8
brvbar; U+000A6
brvbar U+000A6
bscr; U+1D4B7
bsemi; U+0204F
bsim; U+0223D
bsime; U+022CD
bsol; U+0005C
bsolb; U+029C5
bull; U+02022
bullet; U+02022
bump; U+0224E
bumpE; U+02AAE
bumpe; U+0224F
bumpeq; U+0224F
cacute; U+00107
cap; U+02229
capand; U+02A44
capbrcup; U+02A49
capcap; U+02A4B
capcup; U+02A47
capdot; U+02A40
caret; U+02041
caron; U+002C7
ccaps; U+02A4D
ccaron; U+0010D
ccedil; U+000E7
ccedil U+000E7
ccirc; U+00109
ccups; U+02A4C
ccupssm; U+02A50
cdot; U+0010B
cedil; U+000B8
cedil U+000B8
cemptyv; U+029B2
cent; U+000A2
cent U+000A2
centerdot; U+000B7
cfr; U+1D520
chcy; U+00447
check; U+02713
checkmark; U+02713
chi; U+003C7
cir; U+025CB
cirE; U+029C3
circ; U+002C6
circeq; U+02257
circlearrowleft; U+021BA
circlearrowright; U+021BB
circledR; U+000AE
circledS; U+024C8
circledast; U+0229B
circledcirc; U+0229A
circleddash; U+0229D
cire; U+02257
cirfnint; U+02A10
cirmid; U+02AEF
cirscir; U+029C2
clubs; U+02663
clubsuit; U+02663
colon; U+0003A
colone; U+02254
coloneq; U+02254
comma; U+0002C
commat; U+00040
comp; U+02201
compfn; U+02218
complement; U+02201
complexes; U+02102
cong; U+02245
congdot; U+02A6D
conint; U+0222E
copf; U+1D554
coprod; U+02210
copy; U+000A9
copy U+000A9
copysr; U+02117
crarr; U+021B5
cross; U+02717
cscr; U+1D4B8
csub; U+02ACF
csube; U+02AD1
csup; U+02AD0
csupe; U+02AD2
ctdot; U+022EF
cudarrl; U+02938
cudarrr; U+02935
cuepr; U+022DE
cuesc; U+022DF
cularr; U+021B6
cularrp; U+0293D
cup; U+0222A
cupbrcap; U+02A48
cupcap; U+02A46
cupcup; U+02A4A
cupdot; U+0228D
cupor; U+02A45
curarr; U+021B7
curarrm; U+0293C
curlyeqprec; U+022DE
curlyeqsucc; U+022DF
curlyvee; U+022CE
curlywedge; U+022CF
curren; U+000A4
curren U+000A4
curvearrowleft; U+021B6
curvearrowright; U+021B7
cuvee; U+022CE
cuwed; U+022CF
cwconint; U+02232
cwint; U+02231
cylcty; U+0232D
dArr; U+021D3
dHar; U+02965
dagger; U+02020
daleth; U+02138
darr; U+02193
dash; U+02010
dashv; U+022A3
dbkarow; U+0290F
dblac; U+002DD
dcaron; U+0010F
dcy; U+00434
dd; U+02146
ddagger; U+02021
ddarr; U+021CA
ddotseq; U+02A77
deg; U+000B0
deg U+000B0
delta; U+003B4
demptyv; U+029B1
dfisht; U+0297F
dfr; U+1D521
dharl; U+021C3
dharr; U+021C2
diam; U+022C4
diamond; U+022C4
diamondsuit; U+02666
diams; U+02666
die; U+000A8
digamma; U+003DD
disin; U+022F2
div; U+000F7
divide; U+000F7
divide U+000F7
divideontimes; U+022C7
divonx; U+022C7
djcy; U+00452
dlcorn; U+0231E
dlcrop; U+0230D
dollar; U+00024
dopf; U+1D555
dot; U+002D9
doteq; U+02250
doteqdot; U+02251
dotminus; U+02238
dotplus; U+02214
dotsquare; U+022A1
doublebarwedge; U+02306
downarrow; U+02193
downdownarrows; U+021CA
downharpoonleft; U+021C3
downharpoonright; U+021C2
drbkarow; U+02910
drcorn; U+0231F
drcrop; U+0230C
dscr; U+1D4B9
dscy; U+00455
dsol; U+029F6
dstrok; U+00111
dtdot; U+022F1
dtri; U+025BF
dtrif; U+025BE
duarr; U+021F5
duhar; U+0296F
dwangle; U+029A6
dzcy; U+0045F
dzigrarr; U+027FF
eDDot; U+02A77
eDot; U+02251
eacute; U+000E9
eacute U+000E9
easter; U+02A6E
ecaron; U+0011B
ecir; U+02256
ecirc; U+000EA
ecirc U+000EA
ecolon; U+02255
ecy; U+0044D
edot; U+00117
ee; U+02147
efDot; U+02252
efr; U+1D522
eg; U+02A9A
egrave; U+000E8
egrave U+000E8
egs; U+02A96
egsdot; U+02A98
el; U+02A99
elinters; U+023E7
ell; U+02113
els; U+02A95
elsdot; U+02A97
emacr; U+00113
empty; U+02205
emptyset; U+02205
emptyv; U+02205
emsp13; U+02004
emsp14; U+02005
emsp; U+02003
eng; U+0014B
ensp; U+02002
eogon; U+00119
eopf; U+1D556
epar; U+022D5
eparsl; U+029E3
eplus; U+02A71
epsi; U+003F5
epsilon; U+003B5
epsiv; U+003B5
eqcirc; U+02256
eqcolon; U+02255
eqsim; U+02242
eqslantgtr; U+02A96
eqslantless; U+02A95
equals; U+0003D
equest; U+0225F
equiv; U+02261
equivDD; U+02A78
eqvparsl; U+029E5
erDot; U+02253
erarr; U+02971
escr; U+0212F
esdot; U+02250
esim; U+02242
eta; U+003B7
eth; U+000F0
eth U+000F0
euml; U+000EB
euml U+000EB
euro; U+020AC
excl; U+00021
exist; U+02203
expectation; U+02130
exponentiale; U+02147
fallingdotseq; U+02252
fcy; U+00444
female; U+02640
ffilig; U+0FB03
fflig; U+0FB00
ffllig; U+0FB04
ffr; U+1D523
filig; U+0FB01
flat; U+0266D
fllig; U+0FB02
fltns; U+025B1
fnof; U+00192
fopf; U+1D557
forall; U+02200
fork; U+022D4
forkv; U+02AD9
fpartint; U+02A0D
frac12; U+000BD
frac12 U+000BD
frac13; U+02153
frac14; U+000BC
frac14 U+000BC
frac15; U+02155
frac16; U+02159
frac18; U+0215B
frac23; U+02154
frac25; U+02156
frac34; U+000BE
frac34 U+000BE
frac35; U+02157
frac38; U+0215C
frac45; U+02158
frac56; U+0215A
frac58; U+0215D
frac78; U+0215E
frasl; U+02044
frown; U+02322
fscr; U+1D4BB
gE; U+02267
gEl; U+02A8C
gacute; U+001F5
gamma; U+003B3
gammad; U+003DD
gap; U+02A86
gbreve; U+0011F
gcirc; U+0011D
gcy; U+00433
gdot; U+00121
ge; U+02265
gel; U+022DB
geq; U+02265
geqq; U+02267
geqslant; U+02A7E
ges; U+02A7E
gescc; U+02AA9
gesdot; U+02A80
gesdoto; U+02A82
gesdotol; U+02A84
gesles; U+02A94
gfr; U+1D524
gg; U+0226B
ggg; U+022D9
gimel; U+02137
gjcy; U+00453
gl; U+02277
glE; U+02A92
gla; U+02AA5
glj; U+02AA4
gnE; U+02269
gnap; U+02A8A
gnapprox; U+02A8A
gne; U+02A88
gneq; U+02A88
gneqq; U+02269
gnsim; U+022E7
gopf; U+1D558
grave; U+00060
gscr; U+0210A
gsim; U+02273
gsime; U+02A8E
gsiml; U+02A90
gt; U+0003E
gt U+0003E
gtcc; U+02AA7
gtcir; U+02A7A
gtdot; U+022D7
gtlPar; U+02995
gtquest; U+02A7C
gtrapprox; U+02A86
gtrarr; U+02978
gtrdot; U+022D7
gtreqless; U+022DB
gtreqqless; U+02A8C
gtrless; U+02277
gtrsim; U+02273
hArr; U+021D4
hairsp; U+0200A
half; U+000BD
hamilt; U+0210B
hardcy; U+0044A
harr; U+02194
harrcir; U+02948
harrw; U+021AD
hbar; U+0210F
hcirc; U+00125
hearts; U+02665
heartsuit; U+02665
hellip; U+02026
hercon; U+022B9
hfr; U+1D525
hksearow; U+02925
hkswarow; U+02926
hoarr; U+021FF
homtht; U+0223B
hookleftarrow; U+021A9
hookrightarrow; U+021AA
hopf; U+1D559
horbar; U+02015
hscr; U+1D4BD
hslash; U+0210F
hstrok; U+00127
hybull; U+02043
hyphen; U+02010
iacute; U+000ED
iacute U+000ED
ic; U+02063
icirc; U+000EE
icirc U+000EE
icy; U+00438
iecy; U+00435
iexcl; U+000A1
iexcl U+000A1
iff; U+021D4
ifr; U+1D526
igrave; U+000EC
igrave U+000EC
ii; U+02148
iiiint; U+02A0C
iiint; U+0222D
iinfin; U+029DC
iiota; U+02129
ijlig; U+00133
imacr; U+0012B
image; U+02111
imagline; U+02110
imagpart; U+02111
imath; U+00131
imof; U+022B7
imped; U+001B5
in; U+02208
incare; U+02105
infin; U+0221E
infintie; U+029DD
inodot; U+00131
int; U+0222B
intcal; U+022BA
integers; U+02124
intercal; U+022BA
intlarhk; U+02A17
intprod; U+02A3C
iocy; U+00451
iogon; U+0012F
iopf; U+1D55A
iota; U+003B9
iprod; U+02A3C
iquest; U+000BF
iquest U+000BF
iscr; U+1D4BE
isin; U+02208
isinE; U+022F9
isindot; U+022F5
isins; U+022F4
isinsv; U+022F3
isinv; U+02208
it; U+02062
itilde; U+00129
iukcy; U+00456
iuml; U+000EF
iuml U+000EF
jcirc; U+00135
jcy; U+00439
jfr; U+1D527
jmath; U+00237
jopf; U+1D55B
jscr; U+1D4BF
jsercy; U+00458
jukcy; U+00454
kappa; U+003BA
kappav; U+003F0
kcedil; U+00137
kcy; U+0043A
kfr; U+1D528
kgreen; U+00138
khcy; U+00445
kjcy; U+0045C
kopf; U+1D55C
kscr; U+1D4C0
lAarr; U+021DA
lArr; U+021D0
lAtail; U+0291B
lBarr; U+0290E
lE; U+02266
lEg; U+02A8B
lHar; U+02962
lacute; U+0013A
laemptyv; U+029B4
lagran; U+02112
lambda; U+003BB
lang; U+027E8
langd; U+02991
langle; U+027E8
lap; U+02A85
laquo; U+000AB
laquo U+000AB
larr; U+02190
larrb; U+021E4
larrbfs; U+0291F
larrfs; U+0291D
larrhk; U+021A9
larrlp; U+021AB
larrpl; U+02939
larrsim; U+02973
larrtl; U+021A2
lat; U+02AAB
latail; U+02919
late; U+02AAD
lbarr; U+0290C
lbbrk; U+02772
lbrace; U+0007B
lbrack; U+0005B
lbrke; U+0298B
lbrksld; U+0298F
lbrkslu; U+0298D
lcaron; U+0013E
lcedil; U+0013C
lceil; U+02308
lcub; U+0007B
lcy; U+0043B
ldca; U+02936
ldquo; U+0201C
ldquor; U+0201E
ldrdhar; U+02967
ldrushar; U+0294B
ldsh; U+021B2
le; U+02264
leftarrow; U+02190
leftarrowtail; U+021A2
leftharpoondown; U+021BD
leftharpoonup; U+021BC
leftleftarrows; U+021C7
leftrightarrow; U+02194
leftrightarrows; U+021C6
leftrightharpoons; U+021CB
leftrightsquigarrow; U+021AD
leftthreetimes; U+022CB
leg; U+022DA
leq; U+02264
leqq; U+02266
leqslant; U+02A7D
les; U+02A7D
lescc; U+02AA8
lesdot; U+02A7F
lesdoto; U+02A81
lesdotor; U+02A83
lesges; U+02A93
lessapprox; U+02A85
lessdot; U+022D6
lesseqgtr; U+022DA
lesseqqgtr; U+02A8B
lessgtr; U+02276
lesssim; U+02272
lfisht; U+0297C
lfloor; U+0230A
lfr; U+1D529
lg; U+02276
lgE; U+02A91
lhard; U+021BD
lharu; U+021BC
lharul; U+0296A
lhblk; U+02584
ljcy; U+00459
ll; U+0226A
llarr; U+021C7
llcorner; U+0231E
llhard; U+0296B
lltri; U+025FA
lmidot; U+00140
lmoust; U+023B0
lmoustache; U+023B0
lnE; U+02268
lnap; U+02A89
lnapprox; U+02A89
lne; U+02A87
lneq; U+02A87
lneqq; U+02268
lnsim; U+022E6
loang; U+027EC
loarr; U+021FD
lobrk; U+027E6
longleftarrow; U+027F5
longleftrightarrow; U+027F7
longmapsto; U+027FC
longrightarrow; U+027F6
looparrowleft; U+021AB
looparrowright; U+021AC
lopar; U+02985
lopf; U+1D55D
loplus; U+02A2D
lotimes; U+02A34
lowast; U+02217
lowbar; U+0005F
loz; U+025CA
lozenge; U+025CA
lozf; U+029EB
lpar; U+00028
lparlt; U+02993
lrarr; U+021C6
lrcorner; U+0231F
lrhar; U+021CB
lrhard; U+0296D
lrm; U+0200E
lrtri; U+022BF
lsaquo; U+02039
lscr; U+1D4C1
lsh; U+021B0
lsim; U+02272
lsime; U+02A8D
lsimg; U+02A8F
lsqb; U+0005B
lsquo; U+02018
lsquor; U+0201A
lstrok; U+00142
lt; U+0003C
lt U+0003C
ltcc; U+02AA6
ltcir; U+02A79
ltdot; U+022D6
lthree; U+022CB
ltimes; U+022C9
ltlarr; U+02976
ltquest; U+02A7B
ltrPar; U+02996
ltri; U+025C3
ltrie; U+022B4
ltrif; U+025C2
lurdshar; U+0294A
luruhar; U+02966
mDDot; U+0223A
macr; U+000AF
macr U+000AF
male; U+02642
malt; U+02720
maltese; U+02720
map; U+021A6
mapsto; U+021A6
mapstodown; U+021A7
mapstoleft; U+021A4
mapstoup; U+021A5
marker; U+025AE
mcomma; U+02A29
mcy; U+0043C
mdash; U+02014
measuredangle; U+02221
mfr; U+1D52A
mho; U+02127
micro; U+000B5
micro U+000B5
mid; U+02223
midast; U+0002A
midcir; U+02AF0
middot; U+000B7
middot U+000B7
minus; U+02212
minusb; U+0229F
minusd; U+02238
minusdu; U+02A2A
mlcp; U+02ADB
mldr; U+02026
mnplus; U+02213
models; U+022A7
mopf; U+1D55E
mp; U+02213
mscr; U+1D4C2
mstpos; U+0223E
mu; U+003BC
multimap; U+022B8
mumap; U+022B8
nLeftarrow; U+021CD
nLeftrightarrow; U+021CE
nRightarrow; U+021CF
nVDash; U+022AF
nVdash; U+022AE
nabla; U+02207
nacute; U+00144
nap; U+02249
napos; U+00149
napprox; U+02249
natur; U+0266E
natural; U+0266E
naturals; U+02115
nbsp; U+000A0
nbsp U+000A0
ncap; U+02A43
ncaron; U+00148
ncedil; U+00146
ncong; U+02247
ncup; U+02A42
ncy; U+0043D
ndash; U+02013
ne; U+02260
neArr; U+021D7
nearhk; U+02924
nearr; U+02197
nearrow; U+02197
nequiv; U+02262
nesear; U+02928
nexist; U+02204
nexists; U+02204
nfr; U+1D52B
nge; U+02271
ngeq; U+02271
ngsim; U+02275
ngt; U+0226F
ngtr; U+0226F
nhArr; U+021CE
nharr; U+021AE
nhpar; U+02AF2
ni; U+0220B
nis; U+022FC
nisd; U+022FA
niv; U+0220B
njcy; U+0045A
nlArr; U+021CD
nlarr; U+0219A
nldr; U+02025
nle; U+02270
nleftarrow; U+0219A
nleftrightarrow; U+021AE
nleq; U+02270
nless; U+0226E
nlsim; U+02274
nlt; U+0226E
nltri; U+022EA
nltrie; U+022EC
nmid; U+02224
nopf; U+1D55F
not; U+000AC
not U+000AC
notin; U+02209
notinva; U+02209
notinvb; U+022F7
notinvc; U+022F6
notni; U+0220C
notniva; U+0220C
notnivb; U+022FE
notnivc; U+022FD
npar; U+02226
nparallel; U+02226
npolint; U+02A14
npr; U+02280
nprcue; U+022E0
nprec; U+02280
nrArr; U+021CF
nrarr; U+0219B
nrightarrow; U+0219B
nrtri; U+022EB
nrtrie; U+022ED
nsc; U+02281
nsccue; U+022E1
nscr; U+1D4C3
nshortmid; U+02224
nshortparallel; U+02226
nsim; U+02241
nsime; U+02244
nsimeq; U+02244
nsmid; U+02224
nspar; U+02226
nsqsube; U+022E2
nsqsupe; U+022E3
nsub; U+02284
nsube; U+02288
nsubseteq; U+02288
nsucc; U+02281
nsup; U+02285
nsupe; U+02289
nsupseteq; U+02289
ntgl; U+02279
ntilde; U+000F1
ntilde U+000F1
ntlg; U+02278
ntriangleleft; U+022EA
ntrianglelefteq; U+022EC
ntriangleright; U+022EB
ntrianglerighteq; U+022ED
nu; U+003BD
num; U+00023
numero; U+02116
numsp; U+02007
nvDash; U+022AD
nvHarr; U+02904
nvdash; U+022AC
nvinfin; U+029DE
nvlArr; U+02902
nvrArr; U+02903
nwArr; U+021D6
nwarhk; U+02923
nwarr; U+02196
nwarrow; U+02196
nwnear; U+02927
oS; U+024C8
oacute; U+000F3
oacute U+000F3
oast; U+0229B
ocir; U+0229A
ocirc; U+000F4
ocirc U+000F4
ocy; U+0043E
odash; U+0229D
odblac; U+00151
odiv; U+02A38
odot; U+02299
odsold; U+029BC
oelig; U+00153
ofcir; U+029BF
ofr; U+1D52C
ogon; U+002DB
ograve; U+000F2
ograve U+000F2
ogt; U+029C1
ohbar; U+029B5
ohm; U+02126
oint; U+0222E
olarr; U+021BA
olcir; U+029BE
olcross; U+029BB
oline; U+0203E
olt; U+029C0
omacr; U+0014D
omega; U+003C9
omicron; U+003BF
omid; U+029B6
ominus; U+02296
oopf; U+1D560
opar; U+029B7
operp; U+029B9
oplus; U+02295
or; U+02228
orarr; U+021BB
ord; U+02A5D
order; U+02134
orderof; U+02134
ordf; U+000AA
ordf U+000AA
ordm; U+000BA
ordm U+000BA
origof; U+022B6
oror; U+02A56
orslope; U+02A57
orv; U+02A5B
oscr; U+02134
oslash; U+000F8
oslash U+000F8
osol; U+02298
otilde; U+000F5
otilde U+000F5
otimes; U+02297
otimesas; U+02A36
ouml; U+000F6
ouml U+000F6
ovbar; U+0233D
par; U+02225
para; U+000B6
para U+000B6
parallel; U+02225
parsim; U+02AF3
parsl; U+02AFD
part; U+02202
pcy; U+0043F
percnt; U+00025
period; U+0002E
permil; U+02030
perp; U+022A5
pertenk; U+02031
pfr; U+1D52D
phi; U+003C6
phiv; U+003C6
phmmat; U+02133
phone; U+0260E
pi; U+003C0
pitchfork; U+022D4
piv; U+003D6
planck; U+0210F
planckh; U+0210E
plankv; U+0210F
plus; U+0002B
plusacir; U+02A23
plusb; U+0229E
pluscir; U+02A22
plusdo; U+02214
plusdu; U+02A25
pluse; U+02A72
plusmn; U+000B1
plusmn U+000B1
plussim; U+02A26
plustwo; U+02A27
pm; U+000B1
pointint; U+02A15
popf; U+1D561
pound; U+000A3
pound U+000A3
pr; U+0227A
prE; U+02AB3
prap; U+02AB7
prcue; U+0227C
pre; U+02AAF
prec; U+0227A
precapprox; U+02AB7
preccurlyeq; U+0227C
preceq; U+02AAF
precnapprox; U+02AB9
precneqq; U+02AB5
precnsim; U+022E8
precsim; U+0227E
prime; U+02032
primes; U+02119
prnE; U+02AB5
prnap; U+02AB9
prnsim; U+022E8
prod; U+0220F
profalar; U+0232E
profline; U+02312
profsurf; U+02313
prop; U+0221D
propto; U+0221D
prsim; U+0227E
prurel; U+022B0
pscr; U+1D4C5
psi; U+003C8
puncsp; U+02008
qfr; U+1D52E
qint; U+02A0C
qopf; U+1D562
qprime; U+02057
qscr; U+1D4C6
quaternions; U+0210D
quatint; U+02A16
quest; U+0003F
questeq; U+0225F
quot; U+00022
quot U+00022
rAarr; U+021DB
rArr; U+021D2
rAtail; U+0291C
rBarr; U+0290F
rHar; U+02964
race; U+029DA
racute; U+00155
radic; U+0221A
raemptyv; U+029B3
rang; U+027E9
rangd; U+02992
range; U+029A5
rangle; U+027E9
raquo; U+000BB
raquo U+000BB
rarr; U+02192
rarrap; U+02975
rarrb; U+021E5
rarrbfs; U+02920
rarrc; U+02933
rarrfs; U+0291E
rarrhk; U+021AA
rarrlp; U+021AC
rarrpl; U+02945
rarrsim; U+02974
rarrtl; U+021A3
rarrw; U+0219D
ratail; U+0291A
ratio; U+02236
rationals; U+0211A
rbarr; U+0290D
rbbrk; U+02773
rbrace; U+0007D
rbrack; U+0005D
rbrke; U+0298C
rbrksld; U+0298E
rbrkslu; U+02990
rcaron; U+00159
rcedil; U+00157
rceil; U+02309
rcub; U+0007D
rcy; U+00440
rdca; U+02937
rdldhar; U+02969
rdquo; U+0201D
rdquor; U+0201D
rdsh; U+021B3
real; U+0211C
realine; U+0211B
realpart; U+0211C
reals; U+0211D
rect; U+025AD
reg; U+000AE
reg U+000AE
rfisht; U+0297D
rfloor; U+0230B
rfr; U+1D52F
rhard; U+021C1
rharu; U+021C0
rharul; U+0296C
rho; U+003C1
rhov; U+003F1
rightarrow; U+02192
rightarrowtail; U+021A3
rightharpoondown; U+021C1
rightharpoonup; U+021C0
rightleftarrows; U+021C4
rightleftharpoons; U+021CC
rightrightarrows; U+021C9
rightsquigarrow; U+0219D
rightthreetimes; U+022CC
ring; U+002DA
risingdotseq; U+02253
rlarr; U+021C4
rlhar; U+021CC
rlm; U+0200F
rmoust; U+023B1
rmoustache; U+023B1
rnmid; U+02AEE
roang; U+027ED
roarr; U+021FE
robrk; U+027E7
ropar; U+02986
ropf; U+1D563
roplus; U+02A2E
rotimes; U+02A35
rpar; U+00029
rpargt; U+02994
rppolint; U+02A12
rrarr; U+021C9
rsaquo; U+0203A
rscr; U+1D4C7
rsh; U+021B1
rsqb; U+0005D
rsquo; U+02019
rsquor; U+02019
rthree; U+022CC
rtimes; U+022CA
rtri; U+025B9
rtrie; U+022B5
rtrif; U+025B8
rtriltri; U+029CE
ruluhar; U+02968
rx; U+0211E
sacute; U+0015B
sbquo; U+0201A
sc; U+0227B
scE; U+02AB4
scap; U+02AB8
scaron; U+00161
sccue; U+0227D
sce; U+02AB0
scedil; U+0015F
scirc; U+0015D
scnE; U+02AB6
scnap; U+02ABA
scnsim; U+022E9
scpolint; U+02A13
scsim; U+0227F
scy; U+00441
sdot; U+022C5
sdotb; U+022A1
sdote; U+02A66
seArr; U+021D8
searhk; U+02925
searr; U+02198
searrow; U+02198
sect; U+000A7
sect U+000A7
semi; U+0003B
seswar; U+02929
setminus; U+02216
setmn; U+02216
sext; U+02736
sfr; U+1D530
sfrown; U+02322
sharp; U+0266F
shchcy; U+00449
shcy; U+00448
shortmid; U+02223
shortparallel; U+02225
shy; U+000AD
shy U+000AD
sigma; U+003C3
sigmaf; U+003C2
sigmav; U+003C2
sim; U+0223C
simdot; U+02A6A
sime; U+02243
simeq; U+02243
simg; U+02A9E
simgE; U+02AA0
siml; U+02A9D
simlE; U+02A9F
simne; U+02246
simplus; U+02A24
simrarr; U+02972
slarr; U+02190
smallsetminus; U+02216
smashp; U+02A33
smeparsl; U+029E4
smid; U+02223
smile; U+02323
smt; U+02AAA
smte; U+02AAC
softcy; U+0044C
sol; U+0002F
solb; U+029C4
solbar; U+0233F
sopf; U+1D564
spades; U+02660
spadesuit; U+02660
spar; U+02225
sqcap; U+02293
sqcup; U+02294
sqsub; U+0228F
sqsube; U+02291
sqsubset; U+0228F
sqsubseteq; U+02291
sqsup; U+02290
sqsupe; U+02292
sqsupset; U+02290
sqsupseteq; U+02292
squ; U+025A1
square; U+025A1
squarf; U+025AA
squf; U+025AA
srarr; U+02192
sscr; U+1D4C8
ssetmn; U+02216
ssmile; U+02323
sstarf; U+022C6
star; U+02606
starf; U+02605
straightepsilon; U+003F5
straightphi; U+003D5
strns; U+000AF
sub; U+02282
subE; U+02AC5
subdot; U+02ABD
sube; U+02286
subedot; U+02AC3
submult; U+02AC1
subnE; U+02ACB
subne; U+0228A
subplus; U+02ABF
subrarr; U+02979
subset; U+02282
subseteq; U+02286
subseteqq; U+02AC5
subsetneq; U+0228A
subsetneqq; U+02ACB
subsim; U+02AC7
subsub; U+02AD5
subsup; U+02AD3
succ; U+0227B
succapprox; U+02AB8
succcurlyeq; U+0227D
succeq; U+02AB0
succnapprox; U+02ABA
succneqq; U+02AB6
succnsim; U+022E9
succsim; U+0227F
sum; U+02211
sung; U+0266A
sup1; U+000B9
sup1 U+000B9
sup2; U+000B2
sup2 U+000B2
sup3; U+000B3
sup3 U+000B3
sup; U+02283
supE; U+02AC6
supdot; U+02ABE
supdsub; U+02AD8
supe; U+02287
supedot; U+02AC4
suphsub; U+02AD7
suplarr; U+0297B
supmult; U+02AC2
supnE; U+02ACC
supne; U+0228B
supplus; U+02AC0
supset; U+02283
supseteq; U+02287
supseteqq; U+02AC6
supsetneq; U+0228B
supsetneqq; U+02ACC
supsim; U+02AC8
supsub; U+02AD4
supsup; U+02AD6
swArr; U+021D9
swarhk; U+02926
swarr; U+02199
swarrow; U+02199
swnwar; U+0292A
szlig; U+000DF
szlig U+000DF
target; U+02316
tau; U+003C4
tbrk; U+023B4
tcaron; U+00165
tcedil; U+00163
tcy; U+00442
tdot; U+020DB
telrec; U+02315
tfr; U+1D531
there4; U+02234
therefore; U+02234
theta; U+003B8
thetasym; U+003D1
thetav; U+003D1
thickapprox; U+02248
thicksim; U+0223C
thinsp; U+02009
thkap; U+02248
thksim; U+0223C
thorn; U+000FE
thorn U+000FE
tilde; U+002DC
times; U+000D7
times U+000D7
timesb; U+022A0
timesbar; U+02A31
timesd; U+02A30
tint; U+0222D
toea; U+02928
top; U+022A4
topbot; U+02336
topcir; U+02AF1
topf; U+1D565
topfork; U+02ADA
tosa; U+02929
tprime; U+02034
trade; U+02122
triangle; U+025B5
triangledown; U+025BF
triangleleft; U+025C3
trianglelefteq; U+022B4
triangleq; U+0225C
triangleright; U+025B9
trianglerighteq; U+022B5
tridot; U+025EC
trie; U+0225C
triminus; U+02A3A
triplus; U+02A39
trisb; U+029CD
tritime; U+02A3B
trpezium; U+023E2
tscr; U+1D4C9
tscy; U+00446
tshcy; U+0045B
tstrok; U+00167
twixt; U+0226C
twoheadleftarrow; U+0219E
twoheadrightarrow; U+021A0
uArr; U+021D1
uHar; U+02963
uacute; U+000FA
uacute U+000FA
uarr; U+02191
ubrcy; U+0045E
ubreve; U+0016D
ucirc; U+000FB
ucirc U+000FB
ucy; U+00443
udarr; U+021C5
udblac; U+00171
udhar; U+0296E
ufisht; U+0297E
ufr; U+1D532
ugrave; U+000F9
ugrave U+000F9
uharl; U+021BF
uharr; U+021BE
uhblk; U+02580
ulcorn; U+0231C
ulcorner; U+0231C
ulcrop; U+0230F
ultri; U+025F8
umacr; U+0016B
uml; U+000A8
uml U+000A8
uogon; U+00173
uopf; U+1D566
uparrow; U+02191
updownarrow; U+02195
upharpoonleft; U+021BF
upharpoonright; U+021BE
uplus; U+0228E
upsi; U+003C5
upsih; U+003D2
upsilon; U+003C5
upuparrows; U+021C8
urcorn; U+0231D
urcorner; U+0231D
urcrop; U+0230E
uring; U+0016F
urtri; U+025F9
uscr; U+1D4CA
utdot; U+022F0
utilde; U+00169
utri; U+025B5
utrif; U+025B4
uuarr; U+021C8
uuml; U+000FC
uuml U+000FC
uwangle; U+029A7
vArr; U+021D5
vBar; U+02AE8
vBarv; U+02AE9
vDash; U+022A8
vangrt; U+0299C
varepsilon; U+003B5
varkappa; U+003F0
varnothing; U+02205
varphi; U+003C6
varpi; U+003D6
varpropto; U+0221D
varr; U+02195
varrho; U+003F1
varsigma; U+003C2
vartheta; U+003D1
vartriangleleft; U+022B2
vartriangleright; U+022B3
vcy; U+00432
vdash; U+022A2
vee; U+02228
veebar; U+022BB
veeeq; U+0225A
vellip; U+022EE
verbar; U+0007C
vert; U+0007C
vfr; U+1D533
vltri; U+022B2
vopf; U+1D567
vprop; U+0221D
vrtri; U+022B3
vscr; U+1D4CB
vzigzag; U+0299A
wcirc; U+00175
wedbar; U+02A5F
wedge; U+02227
wedgeq; U+02259
weierp; U+02118
wfr; U+1D534
wopf; U+1D568
wp; U+02118
wr; U+02240
wreath; U+02240
wscr; U+1D4CC
xcap; U+022C2
xcirc; U+025EF
xcup; U+022C3
xdtri; U+025BD
xfr; U+1D535
xhArr; U+027FA
xharr; U+027F7
xi; U+003BE
xlArr; U+027F8
xlarr; U+027F5
xmap; U+027FC
xnis; U+022FB
xodot; U+02A00
xopf; U+1D569
xoplus; U+02A01
xotime; U+02A02
xrArr; U+027F9
xrarr; U+027F6
xscr; U+1D4CD
xsqcup; U+02A06
xuplus; U+02A04
xutri; U+025B3
xvee; U+022C1
xwedge; U+022C0
yacute; U+000FD
yacute U+000FD
yacy; U+0044F
ycirc; U+00177
ycy; U+0044B
yen; U+000A5
yen U+000A5
yfr; U+1D536
yicy; U+00457
yopf; U+1D56A
yscr; U+1D4CE
yucy; U+0044E
yuml; U+000FF
yuml U+000FF
zacute; U+0017A
zcaron; U+0017E
zcy; U+00437
zdot; U+0017C
zeetrf; U+02128
zeta; U+003B6
zfr; U+1D537
zhcy; U+00436
zigrarr; U+021DD
zopf; U+1D56B
zscr; U+1D4CF
zwj; U+0200D
zwnj; U+0200C

9 The XHTML syntax

This section only describes the rules for XML resources. Rules for text/html resources are discussed in the section above entitled "The HTML syntax".

9.1 Writing XHTML documents

The syntax for using HTML with XML, whether in XHTML documents or embedded in other XML documents, is defined in the XML and Namespaces in XML specifications. [XML] [XMLNS]

This specification does not define any syntax-level requirements beyond those defined for XML proper.

XML documents may contain a DOCTYPE if desired, but this is not required to conform to this specification. This specification does not define a public or system identifier, nor provide a format DTD.

According to the XML specification, XML processors are not guaranteed to process the external DTD subset referenced in the DOCTYPE. This means, for example, that using entity references for characters in XHTML documents is unsafe if they are defined in an external file (except for &lt;, &gt;, &amp;, &quot; and &apos;).

9.2 Parsing XHTML documents

This section describes the relationship between XML and the DOM, with a particular emphasis on how this interacts with HTML.

An XML parser, for the purposes of this specification, is a construct that follows the rules given in the XML specification to map a string of bytes or characters into a Document object.

An XML parser is either associated with a Document object when it is created, or creates one implicitly.

This Document must then be populated with DOM nodes that represent the tree structure of the input passed to the parser, as defined by the XML specification, the Namespaces in XML specification, and the DOM Core specification. DOM mutation events must not fire for the operations that the XML parser performs on the Document's tree, but the user agent must act as if elements and attributes were individually appended and set respectively so as to trigger rules in this specification regarding what happens when an element in inserted into a document or has its attributes set. [XML] [XMLNS] [DOMCORE] [DOMEVENTS]

Certain algorithms in this specification spoon-feed the parser characters one string at a time. In such cases, the XML parser must act as it would have if faced with a single string consisting of the concatenation of all those characters.

When an XML parser creates a script element, it must be marked as being "parser-inserted". If the parser was originally created for the XML fragment parsing algorithm, then the element must be marked as "already executed" also. When the element's end tag is parsed, the user agent must run the script element. If this causes there to be a pending external script, then the user agent must pause until that script has completed loading, and then execute it.

Since the document.write() API is not available for XML documents, much of the complexity in the HTML parser is not needed in the XML parser.

When an XML parser reaches the end of its input, it must stop parsing, following the same rules as the HTML parser.

9.3 Serializing XHTML fragments

The XML fragment serialization algorithm for a Document or Element node either returns a fragment of XML that represents that node or raises an exception.

For Documents, the algorithm must return a string in the form of a document entity, if none of the error cases below apply.

For Elements, the algorithm must return a string in the form of an internal general parsed entity, if none of the error cases below apply.

In both cases, the string returned must be XML namespace-well-formed and must be an isomorphic serialization of all of that node's child nodes, in tree order. User agents may adjust prefixes and namespace declarations in the serialization (and indeed might be forced to do so in some cases to obtain namespace-well-formed XML). User agents may use a combination of regular text, character references, and CDATA sections to represent text nodes in the DOM (and indeed might be forced to use representations that don't match the DOM's, e.g. if a CDATASection node contains the string "]]>").

For Elements, if any of the elements in the serialization are in no namespace, the default namespace in scope for those elements must be explicitly declared as the empty string. (This doesn't apply in the Document case.) [XML] [XMLNS]

If any of the following error cases are found in the DOM subtree being serialized, then the algorithm raises an INVALID_STATE_ERR exception instead of returning a string:

These are the only ways to make a DOM unserializable. The DOM enforces all the other XML constraints; for example, trying to set an attribute with a name that contains an equals sign (=) will raised an INVALID_CHARACTER_ERR exception.

9.4 Parsing XHTML fragments

The XML fragment parsing algorithm for either returns a Document or raises a SYNTAX_ERR exception. Given a string input and an optional context element context, the algorithm is as follows:

  1. Create a new XML parser.

  2. If there is a context element, feed the parser just created the string corresponding to the start tag of that element, declaring all the namespace prefixes that are in scope on that element in the DOM, as well as declaring the default namespace (if any) that is in scope on that element in the DOM.

    A namespace prefix is in scope if the DOM Core lookupNamespaceURI() method on the element would return a non-null value for that prefix.

    The default namespace is the namespace for which the DOM Core isDefaultNamespace() method on the element would return true.

  3. Feed the parser just created the string input.

  4. If there is a context element, feed the parser just created the string corresponding to the end tag of that element.

  5. If there is an XML well-formedness or XML namespace well-formedness error, then raise a SYNTAX_ERR exception and abort these steps.

  6. If there is a context element, then return the child nodes of the root element of the resulting Document, in tree order.

    Otherwise, return the children of the Document object, in tree order.

10 Rendering

User agents are not required present HTML documents in any particular way. However, this section provides a set of suggestions for rendering HTML documents that, if followed, are likely to lead to a user experience that closely resembles the experience intended by the documents' authors. So as to avoid confusion regarding the normativity of this section, RFC2119 terms have not been used. Instead, the term "expected" is used to indicate behavior that will lead to this experience.

10.1 Introduction

In general, user agents are expected to support CSS, and many of the suggestions in this section are expressed in CSS terms. User agents that use other presentation mechanisms can derive their expected behavior by translating from the CSS rules given in this section.

In the absence of style-layer rules to the contrary (e.g. author style sheets), user agents are expected to render an element so that it conveys to the user the meaning that the element represents, as described by this specification.

The suggestions in this section generally assume a visual output medium with a resolution of 96dpi or greater, but HTML is intended to apply to multiple media (it is a media-independent language). User agents are encouraged to adapt the suggestions in this section to their target media.

10.2 The CSS user agent style sheet and presentational hints

10.2.1 Introduction

The CSS rules given in these subsections are, unless otherwise specified, expected to be used as part of the user-agent level style sheet defaults for all documents that contain HTML elements.

Some rules are intended for the author-level zero-specificity presentational hints part of the CSS cascade; these are explicitly called out as presentational hints.

Some of the rules regarding left and right margins are given here as appropriate for elements whose 'direction' property is 'ltr', and are expected to be flipped around on elements whose 'direction' property is 'rtl'. These are marked "LTR-specific".


When the text below says that an attribute attribute on an element element maps to the pixel length property (or properties) properties, it means that if element has an attribute attribute set, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then the user agent is expected to use the parsed value as a pixel length for a presentational hint for properties.

When the text below says that an attribute attribute on an element element maps to the dimension property (or properties) properties, it means that if element has an attribute attribute set, and parsing that attribute's value using the rules for parsing dimension values doesn't generate an error, then the user agent is expected to use the parsed dimension as the value for a presentational hint for properties, with the value given as a pixel length if the dimension was an integer, and with the value given as a percentage if the dimension was a percentage.

10.2.2 Display types

@namespace url(http://www.w3.org/1999/xhtml);

[hidden], area, audio:not([controls]), base, basefont, command,
datalist, head, input[type=hidden], link, menu[type=context], meta,
noembed, noframes, param, script, source, style, title {
  display: none;
}

address, article, aside, blockquote, body, center, dd, dialog, dir,
div, dl, dt, figure, footer, form, h1, h2, h3, h4, h5, h6, header,
hgroup, hr, html, legend, listing, menu, nav, ol, p, plaintext, pre,
rp, section, ul, xmp { display: block; }

table { display: table; }
caption { display: table-caption; }
colgroup { display: table-column-group; }
col { display: table-column; }
thead { display: table-header-group; }
tbody { display: table-row-group; }
tfoot { display: table-footer-group; }
tr { display: table-row; }
td, th { display: table-cell; }

li { display: list-item; }

ruby { display: ruby; }
rt { display: ruby-text; }

For the purposes of the CSS table model, the col element is to be treated as if it was present as many times as its span attribute specifies.

For the purposes of the CSS table model, the colgroup element, if it contains no col element, is to be treated as if it had as many such children as its span attribute specifies.

For the purposes of the CSS table model, the colspan and rowspan attributes on td and th elements are expected to provide the special knowledge regarding cells spanning rows and columns.

For the purposes of the CSS ruby model, runs of descendants of ruby elements that are not rt or rp elements are expected to be wrapped in anonymous boxes whose 'display' property has the value 'ruby-base'.

User agents that do not support correct ruby rendering are expected to render parentheses around the text of rt elements in the absence of rp elements.

The br element is expected to render as if its contents were a single U+000A LINE FEED (LF) character and its 'white-space' property was 'pre'. User agents are expected to support the 'clear' property on inline elements (in order to render br elements with clear attributes) in the manner described in the non-normative note to this effect in CSS2.1.

The user agent is expected to hide noscript elements for whom scripting is enabled, irrespective of CSS rules.

10.2.3 Margins and padding

@namespace url(http://www.w3.org/1999/xhtml);

article, aside, blockquote, dir, dl, figure, listing, menu, nav, ol,
p, plaintext, pre, section, ul, xmp {
  margin-top: 1em; margin-bottom: 1em;
}

dir dir, dir dl, dir menu, dir ol, dir ul,
dl dir, dl dl, dl menu, dl ol, dl ul,
menu dir, menu dl, menu menu, menu ol, menu ul,
ol dir, ol dl, ol menu, ol ol, ol ul,
ul dir, ul dl, ul menu, ul ol, ul ul {
  margin-top: 0; margin-bottom: 0;
}

h1 { margin-top: 0.67em; margin-bottom; 0.67em; }
h2 { margin-top: 0.83em; margin-bottom; 0.83em; }
h3 { margin-top: 1.00em; margin-bottom; 1.00em; }
h4 { margin-top: 1.33em; margin-bottom; 1.33em; }
h5 { margin-top: 1.67em; margin-bottom; 1.67em; }
h6 { margin-top: 2.33em; margin-bottom; 2.33em; }

dd { margin-left: 40px; } /* LTR-specific: use 'margin-right' for rtl elements */
dir, menu, ol, ul { padding-left: 40px; } /* LTR-specific: use 'padding-right' for rtl elements */
blockquote, figure { margin-left: 40px; margin-right: 40px; }

table { border-spacing: 2px; border-collapse: separate; }
td, th { padding: 1px; }

The article, aside, nav, and section elements are expected to affect the margins of h1 elements, based on the nesting depth. If x is a selector that matches elements that are either article, aside, nav, or section elements, then the following rules capture what is expected:

@namespace url(http://www.w3.org/1999/xhtml);

x h1 { margin-top: 0.83em; margin-bottom: 0.83em; }
x x h1 { margin-top: 1.00em; margin-bottom: 1.00em; }
x x x h1 { margin-top: 1.33em; margin-bottom: 1.33em; }
x x x x h1 { margin-top: 1.67em; margin-bottom: 1.67em; }
x x x x x h1 { margin-top: 2.33em; margin-bottom: 2.33em; }

For each property in the table below, given a body element, the first attribute that exists maps to the pixel length property on the body element. If none of the attributes for a property are found, or if the value of the attribute that was found cannot be parsed successfully, then a default value of 8px is expected to be used for that property instead.

Property Source
'margin-top' body element's marginheight attribute
The body element's container frame element's marginheight attribute
body element's topmargin attribute
'margin-right' body element's marginwidth attribute
The body element's container frame element's marginwidth attribute
body element's rightmargin attribute
'margin-bottom' body element's marginheight attribute
The body element's container frame element's marginheight attribute
body element's topmargin attribute
'margin-left' body element's marginwidth attribute
The body element's container frame element's marginwidth attribute
body element's rightmargin attribute

If the body element's Document's browsing context is a nested browsing context, and the browsing context container of that nested browsing context is a frame or iframe element, then the container frame element of the body element is that frame or iframe element. Otherwise, there is no container frame element.


If the Document has a root element, and the Document's browsing context is a nested browsing context, and the browsing context container of that nested browsing context is a frame or iframe element, and that element has a scrolling attribute, then the user agent is expected to compare the value of the attribute in an ASCII case-insensitive manner to the values in the first column of the following table, and if one of them matches, then the user agent is expected to treat that attribute as a presentational hint for the aforementioned root element's 'overflow' property, setting it to the value given in the corresponding cell on the same row in the second column:

Attribute value 'overflow' value
on 'scroll'
scroll 'scroll'
yes 'scroll'
off 'hidden'
noscroll 'hidden'
no 'hidden'
auto 'auto'

The table element's cellspacing attribute maps to the pixel length property 'border-spacing' on the element.

The table element's cellpadding attribute maps to the pixel length properties 'padding-top', 'padding-right', 'padding-bottom', and 'padding-left' of any td and th elements that have corresponding cells in the table corresponding to the table element.

The table element's hspace attribute maps to the dimension properties 'margin-left' and 'margin-right' on the table element.

The table element's vspace attribute maps to the dimension properties 'margin-top' and 'margin-bottom' on the table element.

The table element's height attribute maps to the dimension property 'height' on the table element.

The table element's width attribute maps to the dimension property 'width' on the table element.

The col element's width attribute maps to the dimension property 'width' on the col element.

The tr element's height attribute maps to the dimension property 'height' on the tr element.

The td and th elements' height attributes map to the dimension property 'height' on the element.

The td and th elements' width attributes map to the dimension property 'width' on the element.


In quirks mode, the following rules are also expected to apply:

@namespace url(http://www.w3.org/1999/xhtml);

form { margin-bottom: 1em; }

When a Document is in quirks mode, margins on HTML elements at the top or bottom of the initial containing block, or the top of bottom of td or th elements, are expected to be collapsed to zero.

10.2.4 Alignment

@namespace url(http://www.w3.org/1999/xhtml);

thead, tbody, tfoot, table > tr { vertical-align: middle; }
tr, td, th { vertical-align: inherit; }
sub { vertical-align: sub; }
sup { vertical-align: super; }
th { text-align: center; }

The following rules are also expected to apply, as presentational hints:

@namespace url(http://www.w3.org/1999/xhtml);

table[align=left] { float: left; }
table[align=right] { float: right; }
table[align=center], table[align=abscenter],
table[align=absmiddle], table[align=middle] {
  margin-left: auto; margin-right: auto;
}

caption[align=bottom] { caption-side: bottom; }
p[align=left], h1[align=left], h2[align=left], h3[align=left],
h4[align=left], h5[align=left], h6[align=left] {
  text-align: left;
}
p[align=right], h1[align=right], h2[align=right], h3[align=right],
h4[align=right], h5[align=right], h6[align=right] {
  text-align: right;
}
p[align=center], h1[align=center], h2[align=center], h3[align=center],
h4[align=center], h5[align=center], h6[align=center] {
  text-align: center;
}
p[align=justify], h1[align=justify], h2[align=justify], h3[align=justify],
h4[align=justify], h5[align=justify], h6[align=justify] {
  text-align: justify;
}
col[valign=top], thead[valign=top], tbody[valign=top],
tfoot[valign=top], tr[valign=top], td[valign=top], th[valign=top] {
  vertical-align: top;
}
col[valign=middle], thead[valign=middle], tbody[valign=middle],
tfoot[valign=middle], tr[valign=middle], td[valign=middle], th[valign=middle] {
  vertical-align: middle;
}
col[valign=bottom], thead[valign=bottom], tbody[valign=bottom],
tfoot[valign=bottom], tr[valign=bottom], td[valign=bottom], th[valign=bottom] {
  vertical-align: bottom;
}
col[valign=baseline], thead[valign=baseline], tbody[valign=baseline],
tfoot[valign=baseline], tr[valign=baseline], td[valign=baseline], th[valign=baseline] {
  vertical-align: baseline;
}

The center element, the caption element unless specified otherwise below, and the div element when its align attribute's value is an ASCII case-insensitive match for the string "center", are expected to center text within themselves, as if they had their 'text-align' property set to 'center' in a presentational hint, and to align descendants to the center.

The div, caption, thead, tbody, tfoot, tr, td, and th elements, when they have an align attribute whose value is an ASCII case-insensitive match for the string "left", are expected to left-align text within themselves, as if they had their 'text-align' property set to 'left' in a presentational hint, and to align descendants to the left.

The div, caption, thead, tbody, tfoot, tr, td, and th elements, when they have an align attribute whose value is an ASCII case-insensitive match for the string "right", are expected to right-align text within themselves, as if they had their 'text-align' property set to 'right' in a presentational hint, and to align descendants to the right.

The div, caption, thead, tbody, tfoot, tr, td, and th elements, when they have an align attribute whose value is an ASCII case-insensitive match for the string "justify", are expected to full-justify text within themselves, as if they had their 'text-align' property set to 'justify' in a presentational hint, and to align descendants to the left.

When a user agent is to align descendants of a node, the user agent is expected to align only those descendants that have both their 'margin-left' and 'margin-right' properties computing to a value other than 'auto', that are over-constrained and that have one of those two margins with a used value forced to a greater value, and that do not themselves have an applicable align attribute.

10.2.5 Fonts and colors

@namespace url(http://www.w3.org/1999/xhtml);

address, cite, dfn, em, i, var { font-style: italic; }
b, strong, th { font-weight: bold; }
code, kbd, listing, plaintext, pre, samp, tt, xmp { font-family: monospace; }
h1 { font-size: 2.00em; font-weight: bold; }
h2 { font-size: 1.50em; font-weight: bold; }
h3 { font-size: 1.17em; font-weight: bold; }
h4 { font-size: 1.00em; font-weight: bold; }
h5 { font-size: 0.83em; font-weight: bold; }
h6 { font-size: 0.67em; font-weight: bold; }
big { font-size: larger; }
small, sub, sup { font-size: smaller; }
sub, sup { line-height: normal; }

:link { color: blue; }
:visited { color: purple; }
mark { background: yellow; color: black; }

table, td, th { border-color: gray; }
thead, tbody, tfoot, tr { border-color: inherit; }
table[rules=none], table[rules=groups], table[rules=rows],
table[rules=cols], table[rules=all], table[frames=void],
table[frames=above], table[frames=below], table[frames=hsides],
table[frames=lhs], table[frames=rhs], table[frames=vsides],
table[frames=box], table[frames=border],
table[rules=none] > tr > td, table[rules=none] > tr > th,
table[rules=groups] > tr > td, table[rules=groups] > tr > th,
table[rules=rows] > tr > td, table[rules=rows] > tr > th,
table[rules=cols] > tr > td, table[rules=cols] > tr > th,
table[rules=all] > tr > td, table[rules=all] > tr > th,
table[frames=void] > tr > td, table[frames=void] > tr > th,
table[frames=above] > tr > td, table[frames=above] > tr > th,
table[frames=below] td, table[frames=below] > tr > th,
table[frames=hsides] > tr > td, table[frames=hsides] > tr > th,
table[frames=lhs] > tr > td, table[frames=lhs] > tr > th,
table[frames=rhs] > tr > td, table[frames=rhs] > tr > th,
table[frames=vsides] > tr > td, table[frames=vsides] > tr > th,
table[frames=box] > tr > td, table[frames=box] > tr > th,
table[frames=border] > tr > td, table[frames=border] > tr > th,
table[rules=none] > thead > tr > td, table[rules=none] > thead > tr > th,
table[rules=groups] > thead > tr > td, table[rules=groups] > thead > tr > th,
table[rules=rows] > thead > tr > td, table[rules=rows] > thead > tr > th,
table[rules=cols] > thead > tr > td, table[rules=cols] > thead > tr > th,
table[rules=all] > thead > tr > td, table[rules=all] > thead > tr > th,
table[frames=void] > thead > tr > td, table[frames=void] > thead > tr > th,
table[frames=above] > thead > tr > td, table[frames=above] > thead > tr > th,
table[frames=below] td, table[frames=below] > thead > tr > th,
table[frames=hsides] > thead > tr > td, table[frames=hsides] > thead > tr > th,
table[frames=lhs] > thead > tr > td, table[frames=lhs] > thead > tr > th,
table[frames=rhs] > thead > tr > td, table[frames=rhs] > thead > tr > th,
table[frames=vsides] > thead > tr > td, table[frames=vsides] > thead > tr > th,
table[frames=box] > thead > tr > td, table[frames=box] > thead > tr > th,
table[frames=border] > thead > tr > td, table[frames=border] > thead > tr > th,
table[rules=none] > tbody > tr > td, table[rules=none] > tbody > tr > th,
table[rules=groups] > tbody > tr > td, table[rules=groups] > tbody > tr > th,
table[rules=rows] > tbody > tr > td, table[rules=rows] > tbody > tr > th,
table[rules=cols] > tbody > tr > td, table[rules=cols] > tbody > tr > th,
table[rules=all] > tbody > tr > td, table[rules=all] > tbody > tr > th,
table[frames=void] > tbody > tr > td, table[frames=void] > tbody > tr > th,
table[frames=above] > tbody > tr > td, table[frames=above] > tbody > tr > th,
table[frames=below] td, table[frames=below] > tbody > tr > th,
table[frames=hsides] > tbody > tr > td, table[frames=hsides] > tbody > tr > th,
table[frames=lhs] > tbody > tr > td, table[frames=lhs] > tbody > tr > th,
table[frames=rhs] > tbody > tr > td, table[frames=rhs] > tbody > tr > th,
table[frames=vsides] > tbody > tr > td, table[frames=vsides] > tbody > tr > th,
table[frames=box] > tbody > tr > td, table[frames=box] > tbody > tr > th,
table[frames=border] > tbody > tr > td, table[frames=border] > tbody > tr > th,
table[rules=none] > tfoot > tr > td, table[rules=none] > tfoot > tr > th,
table[rules=groups] > tfoot > tr > td, table[rules=groups] > tfoot > tr > th,
table[rules=rows] > tfoot > tr > td, table[rules=rows] > tfoot > tr > th,
table[rules=cols] > tfoot > tr > td, table[rules=cols] > tfoot > tr > th,
table[rules=all] > tfoot > tr > td, table[rules=all] > tfoot > tr > th,
table[frames=void] > tfoot > tr > td, table[frames=void] > tfoot > tr > th,
table[frames=above] > tfoot > tr > td, table[frames=above] > tfoot > tr > th,
table[frames=below] td, table[frames=below] > tfoot > tr > th,
table[frames=hsides] > tfoot > tr > td, table[frames=hsides] > tfoot > tr > th,
table[frames=lhs] > tfoot > tr > td, table[frames=lhs] > tfoot > tr > th,
table[frames=rhs] > tfoot > tr > td, table[frames=rhs] > tfoot > tr > th,
table[frames=vsides] > tfoot > tr > td, table[frames=vsides] > tfoot > tr > th,
table[frames=box] > tfoot > tr > td, table[frames=box] > tfoot > tr > th,
table[frames=border] > tfoot > tr > td, table[frames=border] > tfoot > tr > th {
  border-color: black;
}


The initial value for the 'color' property is expected to be black. The initial value for the 'background-color' property is expected to be 'transparent'. The canvas's background is expected to be white.


The article, aside, nav, and section elements are expected to affect the font size of h1 elements, based on the nesting depth. If x is a selector that matches elements that are either article, aside, nav, or section elements, then the following rules capture what is expected:

@namespace url(http://www.w3.org/1999/xhtml);

x h1 { font-size: 1.50em; }
x x h1 { font-size: 1.17em; }
x x x h1 { font-size: 1.00em; }
x x x x h1 { font-size: 0.83em; }
x x x x x h1 { font-size: 0.67em; }

When a body, table, thead, tbody, tfoot, tr, td, or th element has a background attribute set to a non-empty value, the new value is expected to be resolved relative to the element, and if this is successful, the user agent is expected to treat the attribute as a presentational hint setting the element's 'background-image' property to the resulting absolute URL.

When a body, table, thead, tbody, tfoot, tr, td, or th element has a bgcolor attribute set, the new value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return an error, the user agent is expected to treat the attribute as a presentational hint setting the element's 'background-color' property to the resulting color.

When a body element has a text attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return an error, the user agent is expected to treat the attribute as a presentational hint setting the element's 'color' property to the resulting color.

When a body element has a link attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return an error, the user agent is expected to treat the attribute as a presentational hint setting the 'color' property of any element in the Document matching the ':link' pseudo-class to the resulting color.

When a body element has a vlink attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return an error, the user agent is expected to treat the attribute as a presentational hint setting the 'color' property of any element in the Document matching the ':visited' pseudo-class to the resulting color.

When a body element has a alink attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return an error, the user agent is expected to treat the attribute as a presentational hint setting the 'color' property of any element in the Document matching the ':active' pseudo-class and either the ':link' pseudo-class or the ':visited' pseudo-class to the resulting color.

When a table element has a bordercolor attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return an error, the user agent is expected to treat the attribute as a presentational hint setting the element's 'border-top-color', 'border-right-color', 'border-bottom-color', and 'border-right-color' properties to the resulting color.


When a font element has a color attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return an error, the user agent is expected to treat the attribute as a presentational hint setting the element's 'color' property to the resulting color.

When a font element has a face attribute, the user agent is expected to treat the attribute as a presentational hint setting the element's 'font-family' property to the attribute's value.

When a font element has a pointsize attribute, the user agent is expected to parse that attribute's value using the rules for parsing non-negative integers, and if this doesn't generate an error, then the user agent is expected to use the parsed value as a point length for a presentational hint for the 'font-size' property on the element.

When a font element has a size attribute, the user agent is expected to use the following steps to treat the attribute as a presentational hint setting the element's 'font-size' property:

  1. Let input be the attribute's value.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Skip whitespace.

  4. If position is past the end of input, there is no presentational hint. Abort these steps.

  5. If the character at position is a U+002B PLUS SIGN character (+), then let mode be relative-plus, and advance position to the next character. Otherwise, if the character at position is a U+002D HYPHEN-MINUS character (-), then let mode be relative-minus, and advance position to the next character. Otherwise, let mode be absolute.

  6. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and let the resulting sequence be digits.

  7. If digits is the empty string, there is no presentational hint. Abort these steps.

  8. Interpret digits as a base-ten integer. Let value be the resulting number.

  9. If mode is relative-plus, then increment value by 3. If mode is relative-minus, then let value be the result of subtracting value from 3.

  10. If value is greater than 7, let it be 7.

  11. If value is less than 1, let it be 1.

  12. Set 'font-size' to the keyword corresponding to the value of value according to the following table:

    value 'font-size' keyword Notes
    1 xx-small
    2 small
    3 medium
    4 large
    5 x-large
    6 xx-large
    7 xxx-large see below

    The 'xxx-large' value is a non-CSS value used here to indicate a font size one "step" larger than 'xx-large'.

10.2.6 Punctuation and decorations

@namespace url(http://www.w3.org/1999/xhtml);

:link, :visited, ins, u { text-decoration: underline; }
abbr[title], acronym[title] { text-decoration: dotted underline; }
del, s, strike { text-decoration: line-through; }
blink { text-decoration: blink; }

q:before { content: open-quote; }
q:after { content: close-quote; }

nobr { white-space: nowrap; }
listing, plaintext, pre, xmp { white-space: pre; }

ol { list-style-type: decimal; }

dir, menu, ul {
  list-style-type: disc;
}

dir dl, dir menu, dir ul,
menu dl, menu menu, menu ul,
ol dl, ol menu, ol ul,
ul dl, ul menu, ul ul {
  list-style-type: circle;
}

dir dir dl, dir dir menu, dir dir ul, 
dir menu dl, dir menu menu, dir menu ul, 
dir ol dl, dir ol menu, dir ol ul, 
dir ul dl, dir ul menu, dir ul ul, 
menu dir dl, menu dir menu, menu dir ul, 
menu menu dl, menu menu menu, menu menu ul, 
menu ol dl, menu ol menu, menu ol ul, 
menu ul dl, menu ul menu, menu ul ul, 
ol dir dl, ol dir menu, ol dir ul, 
ol menu dl, ol menu menu, ol menu ul, 
ol ol dl, ol ol menu, ol ol ul, 
ol ul dl, ol ul menu, ol ul ul, 
ul dir dl, ul dir menu, ul dir ul, 
ul menu dl, ul menu menu, ul menu ul, 
ul ol dl, ul ol menu, ul ol ul, 
ul ul dl, ul ul menu, ul ul ul {
  list-style-type: square;
}

table { border-style: outset; }
td, th { border-style: inset; }

[dir=ltr] { direction: ltr; unicode-bidi: embed; }
[dir=rtl] { direction: rtl; unicode-bidi: embed; }
bdo[dir=ltr], bdo[dir=rtl] { unicode-bidi: bidi-override; }

In addition, rules setting the 'quotes' property appropriately for the locales and languages understood by the user are expected to be present.


The following rules are also expected to apply, as presentational hints:

@namespace url(http://www.w3.org/1999/xhtml);

td[nowrap], th[nowrap] { white-space: nowrap; }
pre[wrap] { white-space: pre-wrap; }

br[clear=left] { clear: left; }
br[clear=right] { clear: right; }
br[clear=all], br[clear=both] { clear: both; }

ol[type=1], li[type=1] { list-style-type: decimal; }
ol[type=a], li[type=a] { list-style-type: lower-alpha; }
ol[type=A], li[type=A] { list-style-type: upper-alpha; }
ol[type=i], li[type=i] { list-style-type: lower-roman; }
ol[type=I], li[type=I] { list-style-type: upper-roman; }
ul[type=disc], li[type=disc] { list-style-type: disc; }
ul[type=circle], li[type=circle] { list-style-type: circle; }
ul[type=square], li[type=square] { list-style-type: square; }

table[rules=none], table[rules=groups], table[rules=rows],
table[rules=cols], table[rules=all] {
  border-style: none;
  border-collapse: collapse;
}

table[frames=void] { border-style: hidden hidden hidden hidden; }
table[frames=above] { border-style: solid hidden hidden hidden; }
table[frames=below] { border-style: hidden hidden solid hidden; }
table[frames=hsides] { border-style: solid hidden solid hidden; }
table[frames=lhs] { border-style: hidden hidden hidden solid; }
table[frames=rhs] { border-style: hidden solid hidden hidden; }
table[frames=vsides] { border-style: hidden solid hidden solid; }
table[frames=box],
table[frames=border] { border-style: solid solid solid solid; }

table[frames=void] > tr > td, table[frames=void] > tr > th,
table[frames=above] > tr > td, table[frames=above] > tr > th,
table[frames=below] > tr > td, table[frames=below] > tr > th,
table[frames=hsides] > tr > td, table[frames=hsides] > tr > th,
table[frames=lhs] > tr > td, table[frames=lhs] > tr > th,
table[frames=rhs] > tr > td, table[frames=rhs] > tr > th,
table[frames=vsides] > tr > td, table[frames=vsides] > tr > th,
table[frames=box] > tr > td, table[frames=box] > tr > th,
table[frames=border] > tr > td, table[frames=border] > tr > th,
table[frames=void] > thead > tr > td, table[frames=void] > thead > tr > th,
table[frames=above] > thead > tr > td, table[frames=above] > thead > tr > th,
table[frames=below] > thead > tr > td, table[frames=below] > thead > tr > th,
table[frames=hsides] > thead > tr > td, table[frames=hsides] > thead > tr > th,
table[frames=lhs] > thead > tr > td, table[frames=lhs] > thead > tr > th,
table[frames=rhs] > thead > tr > td, table[frames=rhs] > thead > tr > th,
table[frames=vsides] > thead > tr > td, table[frames=vsides] > thead > tr > th,
table[frames=box] > thead > tr > td, table[frames=box] > thead > tr > th,
table[frames=border] > thead > tr > td, table[frames=border] > thead > tr > th,
table[frames=void] > tbody > tr > td, table[frames=void] > tbody > tr > th,
table[frames=above] > tbody > tr > td, table[frames=above] > tbody > tr > th,
table[frames=below] > tbody > tr > td, table[frames=below] > tbody > tr > th,
table[frames=hsides] > tbody > tr > td, table[frames=hsides] > tbody > tr > th,
table[frames=lhs] > tbody > tr > td, table[frames=lhs] > tbody > tr > th,
table[frames=rhs] > tbody > tr > td, table[frames=rhs] > tbody > tr > th,
table[frames=vsides] > tbody > tr > td, table[frames=vsides] > tbody > tr > th,
table[frames=box] > tbody > tr > td, table[frames=box] > tbody > tr > th,
table[frames=border] > tbody > tr > td, table[frames=border] > tbody > tr > th,
table[frames=void] > tfoot > tr > td, table[frames=void] > tfoot > tr > th,
table[frames=above] > tfoot > tr > td, table[frames=above] > tfoot > tr > th,
table[frames=below] > tfoot > tr > td, table[frames=below] > tfoot > tr > th,
table[frames=hsides] > tfoot > tr > td, table[frames=hsides] > tfoot > tr > th,
table[frames=lhs] > tfoot > tr > td, table[frames=lhs] > tfoot > tr > th,
table[frames=rhs] > tfoot > tr > td, table[frames=rhs] > tfoot > tr > th,
table[frames=vsides] > tfoot > tr > td, table[frames=vsides] > tfoot > tr > th,
table[frames=box] > tfoot > tr > td, table[frames=box] > tfoot > tr > th,
table[frames=border] > tfoot > tr > td, table[frames=border] > tfoot > tr > th {
  border-style: solid;
}

table[rules=none] > tr > td, table[rules=none] > tr > th,
table[rules=none] > thead > tr > td, table[rules=none] > thead > tr > th,
table[rules=none] > tbody > tr > td, table[rules=none] > tbody > tr > th,
table[rules=none] > tfoot > tr > td, table[rules=none] > tfoot > tr > th,
table[rules=groups] > tr > td, table[rules=groups] > tr > th,
table[rules=groups] > thead > tr > td, table[rules=groups] > thead > tr > th,
table[rules=groups] > tbody > tr > td, table[rules=groups] > tbody > tr > th,
table[rules=groups] > tfoot > tr > td, table[rules=groups] > tfoot > tr > th,
table[rules=rows] > tr > td, table[rules=rows] > tr > th,
table[rules=rows] > thead > tr > td, table[rules=rows] > thead > tr > th,
table[rules=rows] > tbody > tr > td, table[rules=rows] > tbody > tr > th,
table[rules=rows] > tfoot > tr > td, table[rules=rows] > tfoot > tr > th {
  border-style: none;
}

table[rules=groups] > colgroup, table[rules=groups] > thead,
table[rules=groups] > tbody, table[rules=groups] > tfoot {
  border-style: solid;
}

table[rules=rows] > tr, table[rules=rows] > thead > tr,
table[rules=rows] > tbody > tr, table[rules=rows] > tfoot > tr {
  border-style: solid;
}

table[rules=cols] > tr > td, table[rules=cols] > tr > th,
table[rules=cols] > thead > tr > td, table[rules=cols] > thead > tr > th,
table[rules=cols] > tbody > tr > td, table[rules=cols] > tbody > tr > th,
table[rules=cols] > tfoot > tr > td, table[rules=cols] > tfoot > tr > th {
  border-style: none solid none solid;
}

table[rules=all] > tr > td, table[rules=all] > tr > th,
table[rules=all] > thead > tr > td, table[rules=all] > thead > tr > th,
table[rules=all] > tbody > tr > td, table[rules=all] > tbody > tr > th,
table[rules=all] > tfoot > tr > td, table[rules=all] > tfoot > tr > th {
  border-style: solid;
}

When rendering li elements, user agents are expected to use the ordinal value of the li element to render the counter in the list item marker.

The table element's border attribute maps to the pixel length properties 'border-top-width', 'border-right-width', 'border-bottom-width', 'border-left-width' on the element. If the attribute is present but its value cannot be parsed successfully, a default value of 1px is expected to be used for that property instead.

10.2.7 Resetting rules for inherited properties

The following rules are also expected to be in play, resetting certain properties to block inheritance by default.

@namespace url(http://www.w3.org/1999/xhtml);

table, input, select, option, optgroup, button, textarea, keygen {
  text-indent: initial;
}

In quirks mode, the following rules are also expected to apply:

@namespace url(http://www.w3.org/1999/xhtml);

table {
  font-weight: initial;
  font-style: initial;
  font-variant: initial;
  font-size: initial;
  line-height: initial;
  white-space: initial;
  text-align: initial;
}

input { box-sizing: border-box; }

10.2.8 The hr element

@namespace url(http://www.w3.org/1999/xhtml);

hr { color: gray; border-style: inset; border-width: 1px; }

The following rules are also expected to apply, as presentational hints:

@namespace url(http://www.w3.org/1999/xhtml);

hr[align=left] { margin-left: 0; margin-right: auto; }
hr[align=right] { margin-left: auto; margin-right: 0; }
hr[align=center] { margin-left: auto; margin-right: auto; }
hr[color], hr[noshade] { border-style: solid; }

If an hr element has either a color attribute or a noshade attribute, and furthermore also has a size attribute, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then the user agent is expected to use the parsed value divided by two as a pixel length for presentational hints for the properties 'border-top-width', 'border-right-width', 'border-bottom-width', and 'border-left-width' on the element.

Otherwise, if an hr element has neither a color attribute nor a noshade attribute, but does have a size attribute, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then: if the parsed value is one, then the user agent is expected to use the attribute as a presentational hint setting the element's 'border-bottom-width' to 0; otherwise, if the parsed value is greater than one, then the user agent is expected to use the parsed value minus two as a pixel length for presentational hints for the 'height' property on the element.

The width attribute on an hr element maps to the dimension property 'width' on the element.

When an hr element has a color attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return an error, the user agent is expected to treat the attribute as a presentational hint setting the element's 'color' property to the resulting color.

10.2.9 The fieldset element

@namespace url(http://www.w3.org/1999/xhtml);

fieldset {
  margin-left: 2px; margin-right: 2px;
  border: groove 2px ThreeDFace;
  padding: 0.35em 0.625em 0.75em;
}

The fieldset element is expected to establish a new block formatting context.

The first legend element child of a fieldset element, if any, is expected to be rendered over the top border edge of the fieldset element. If the legend element in question has an align attribute, and its value is an ASCII case-insensitive match for one of the strings in the first column of the following table, then the legend is expected to be rendered horizontally aligned over the border edge in the position given in the corresponding cell on the same row in the second column. If the attribute is absent or has a value that doesn't match any of the cases in the table, then the position is expected to be on the right if the 'direction' property on this element has a computed value of 'rtl', and on the left otherwise.

Attribute value Alignment position
left On the left
right On the right
center In the middle

10.3 Replaced elements

10.3.1 Embedded content

The applet, canvas, embed, iframe, and video elements are expected to be treated as replaced elements.

An object element that represents an image, plugin, or nested browsing context is expected to be treated as a replaced element. Other object elements are expected to be treated as ordinary elements in the rendering model.

The audio element, when it has a controls attribute, is expected to be treated as a replaced element about one line high, as wide as is necessary to expose the user agent's user interface features.

The video element's controls attribute is not expected to affect the size of the rendering; controls are expected to be overlaid with the page content without causing any layout changes, and are expected to disappear when the user does not need them.

When a video element represents its poster frame, the poster frame is expected to be rendered at the largest size that maintains the poster frame's aspect ratio without being taller or wider than the video element itself, and is expected to be centered in the video element.

Resizing video and canvas elements does not interrupt video playback or clear the canvas.


The following CSS rules are expected to apply:

@namespace url(http://www.w3.org/1999/xhtml);

iframe { border: 2px inset; }

10.3.2 Images

When an img element or an input element when its type attribute is in the Image Button state represents an image, it is expected to be treated as a replaced element.

When an img element or an input element when its type attribute is in the Image Button state does not represent an image, but the element already has intrinsic dimensions (e.g. from the dimension attributes or CSS rules), and either the user agent has reason to believe that the image will become available and be rendered in due course or the Document is in quirks mode, the element is expected to be treated as a replaced element whose content is the text that the element represents, if any, optionally alongside an icon indicating that the image is being obtained. For input elements, the text is expected to appear button-like to indicate that the element is a button.

When an img element represents some text and the user agent does not expect this to change, the element is expected to be treated as an inline element whose content is the text, optionally with an icon indicating that an image is missing.

When an img element represents nothing and the user agent does not expect this to change, the element is expected to not be rendered at all.

When an img element might be a key part of the content, but neither the image nor any kind of alternative text is available, and the user agent does not expect this to change, the element is expected to be treated as an inline element whose content is an icon indicating that an image is missing.

When an input element whose type attribute is in the Image Button state does not represent an image and the user agent does not expect this to change, the element is expected to be treated as a replaced element consisting of a button whose content is the element's alternative text. The intrinsic dimensions of the button are expected to be about one line in height and whatever width is necessary to render the text on one line.

The icons mentioned above are expected to be relatively small so as not to disrupt most text but be easily clickable. In a visual environment, for instance, icons could be 16 pixels by 16 pixels square, or 1em by 1em if the images are scalable. In an audio environment, the icon could be a short bleep. The icons are intended to indicate to the user that they can be used to get to whatever options the UA provides for images, and, where appropriate, are expected to provide access to the context menu that would have come up if the user interacted with the actual image.


The following CSS rules are expected to apply when the Document is in quirks mode:

@namespace url(http://www.w3.org/1999/xhtml);

img[align=left] { margin-right: 3px; }
img[align=right] { margin-left: 3px; }

10.3.3 Attributes for embedded content and images

The following CSS rules are expected to apply as presentational hints:

@namespace url(http://www.w3.org/1999/xhtml);

iframe[frameborder=0], iframe[frameborder=no] { border: none; }

applet[align=left], embed[align=left], iframe[align=left],
img[align=left], input[type=image][align=left], object[align=left] {
  float: left;
}

applet[align=right], embed[align=right], iframe[align=right],
img[align=right], input[type=image][align=right], object[align=right] {
  float: right;
}

applet[align=top], embed[align=top], iframe[align=top],
img[align=top], input[type=image][align=top], object[align=top] {
  vertical-align: top;
}

applet[align=bottom], embed[align=bottom], iframe[align=bottom],
img[align=bottom], input[type=image][align=bottom], object[align=bottom],
applet[align=baseline], embed[align=baseline], iframe[align=baseline],
img[align=baseline], input[type=image][align=baseline], object[align=baseline] {
  vertical-align: baseline;
}

applet[align=texttop], embed[align=texttop], iframe[align=texttop],
img[align=texttop], input[type=image][align=texttop], object[align=texttop] {
  vertical-align: text-top;
}

applet[align=absmiddle], embed[align=absmiddle], iframe[align=absmiddle],
img[align=absmiddle], input[type=image][align=absmiddle], object[align=absmiddle],
applet[align=abscenter], embed[align=abscenter], iframe[align=abscenter],
img[align=abscenter], input[type=image][align=abscenter], object[align=abscenter] {
  vertical-align: middle;
}

applet[align=bottom], embed[align=bottom], iframe[align=bottom],
img[align=bottom], input[type=image][align=bottom],
object[align=bottom] {
  vertical-align: bottom;
}

When an applet, embed, iframe, img, or object element, or an input element whose type attribute is in the Image Button state, has an align attribute whose value is an ASCII case-insensitive match for the string "center" or the string "middle", the user agent is expected to act as if the element's 'vertical-align' property was set to a value that aligns the vertical middle of the element with the parent element's baseline.

The hspace attribute of applet, embed, iframe, img, or object elements, and input elements with a type attribute in the Image Button state, maps to the dimension properties 'margin-left' and 'margin-right' on the element.

The vspace attribute of applet, embed, iframe, img, or object elements, and input elements with a type attribute in the Image Button state, maps to the dimension properties 'margin-top' and 'margin-bottom' on the element.

When an img element, object element, or input element with a type attribute in the Image Button state is contained within a hyperlink and has a border attribute whose value, when parsed using the rules for parsing non-negative integers, is found to be a number greater than zero, the user agent is expected to use the parsed value for eight presentational hints: four setting the parsed value as a pixel length for the element's 'border-top-width', 'border-right-width', 'border-bottom-width', and 'border-left-width' properties, and four setting the element's 'border-top-style', 'border-right-style', 'border-bottom-style', and 'border-left-style' properties to the value 'solid'.

The width and height attributes on applet, embed, iframe, img, object or video elements, and input elements with a type attribute in the Image Button state, map to the dimension properties 'width' and 'height' on the element respectively.

10.3.4 Image maps

Shapes on an image map are expected to act, for the purpose of the CSS cascade, as elements independent of the original area element that happen to match the same style rules but inherit from the img or object element.

For the purposes of the rendering, only the 'cursor' property is expected to have any effect on the shape.

Thus, for example, if an area element has a style attribute that sets the 'cursor' property to 'help', then when the user designates that shape, the cursor would change to a Help cursor.

Similarly, if an area element had a CSS rule that set its 'cursor' property to 'inherit' (or if no rule setting the 'cursor' property matched the element at all), the shape's cursor would be inherited from the img or object element of the image map, not from the parent of the area element.

10.3.5 Tool bars

When a menu element's type attribute is in the tool bar state, the element is expected to be treated as a replaced element with a height about two lines high and a width derived from the contents of the element.

The element is expected to have, by default, the appearance of a tool bar on the user agent's platform. It is expected to contain the menu that is built from the element.

...example with screenshot...

10.4 Bindings

10.4.1 Introduction

A number of elements have their rendering defined in terms of the 'binding' property. [BECSS]

The CSS snippets below set the 'binding' property to a user-agent-defined value, represented below by keywords like bb. The rules then described for these bindings are only expected to apply if the element's 'binding' property has not been overridden (e.g. by the author) to have another value.

Exactly how the bindings are implemented is not specified by this specification. User agents are encouraged to make their bindings set the 'appearance' CSS property appropriately to achieve platform-native appearances for widgets, and are expected to implement any relevant animations, etc, that are appropriate for the platform. [CSSUI]


The converting a character width to pixels algorithm, used by some of the bindings below, returns (size-1avg + max, where size is the character width to convert, avg is the average character width of the primary font for the element for which the algorithm is being run, in pixels, and max is the maximum character width of that same font, also in pixels. (The element's 'letter-spacing' property does not affect the result.)

10.4.2 The bb element

@namespace url(http://www.w3.org/1999/xhtml);

bb:empty { binding: bb; }

When the bb binding applies to a bb element, the element is expected to render as an 'inline-block' box rendered as a button, about one line high, containing text derived from the element's type attribute in a user-agent-defined (and probably locale-specific) fashion.

10.4.3 The button element

@namespace url(http://www.w3.org/1999/xhtml);

button { binding: button; }

When the button binding applies to a button element, the element is expected to render as an 'inline-block' box rendered as a button whose contents are the contents of the element.

10.4.4 The datagrid element

This section will probably include details on how to render DATAGRID (including its pseudo-elements), drag-and-drop, etc, in a visual medium, in concert with CSS. Implementation experience is desired before this section is filled in.

10.4.5 The details element

@namespace url(http://www.w3.org/1999/xhtml);

details { binding: details; }

When the details binding applies to a details element, the element is expected to render as a 'block' box with its 'padding-left' property set to '40px'. The element's shadow tree is expected to take a child element that matches the selector :bound-element > legend:first-child and place it in a first 'block' box container, and then take the remaining child nodes and place them in a later 'block' box container.

The first container is expected to contain at least one line box, and that line box is expected to contain a triangle widget, horizontally positioned within the left padding of the details element. That widget is expected to allow the user to request that the details be shown or hidden.

The later container is expected to have its 'overflow' property set to 'hidden'. When the details element has an open attribute, the later container is expected to have its 'height' set to 'auto'; when it does not, the later container is expected to have its 'height' set to 0.

10.4.6 The input element as a text entry widget

@namespace url(http://www.w3.org/1999/xhtml);

input { binding: input-textfield; }
input[type=password] { binding: input-password; }
/* later rules override this for other values of type="" */

When the input-textfield binding applies to an input element whose type attribute is in the Text, Search, URL, or E-mail state, the element is expected to render as an 'inline-block' box rendered as a text field.

When the input-password binding applies, to an input element whose type attribute is in the Password state, the element is expected to render as an 'inline-block' box rendered as a text field whose contents are obscured.

If an input element whose type attribute is in one of the above states has a size attribute, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then the user agent is expected to use the attribute as a presentational hint for the 'width' property on the element, with the value obtained from applying the converting a character width to pixels algorithm to the value of the attribute.

If an input element whose type attribute is in one of the above states does not have a size attribute, then the user agent is expected to act as if it had a user-agent-level style sheet rule setting the 'width' property on the element to the value obtained from applying the converting a character width to pixels algorithm to the number 20.

10.4.7 The input element as domain-specific widgets

@namespace url(http://www.w3.org/1999/xhtml);

input[type=datetime] { binding: input-datetime; }
input[type=date] { binding: input-date; }
input[type=month] { binding: input-month; }
input[type=week] { binding: input-week; }
input[type=time] { binding: input-time; }
input[type=datetime-local] { binding: input-datetime-local; }
input[type=number] { binding: input-number; }

When the input-datetime binding applies to an input element whose type attribute is in the Date and Time state, the element is expected to render as an 'inline-block' box depicting a Date and Time control.

When the input-date binding applies to an input element whose type attribute is in the Date state, the element is expected to render as an 'inline-block' box depicting a Date control.

When the input-month binding applies to an input element whose type attribute is in the Month state, the element is expected to render as an 'inline-block' box depicting a Month control.

When the input-week binding applies to an input element whose type attribute is in the Week state, the element is expected to render as an 'inline-block' box depicting a Week control.

When the input-time binding applies to an input element whose type attribute is in the Time state, the element is expected to render as an 'inline-block' box depicting a Time control.

When the input-datetime-local binding applies to an input element whose type attribute is in the Local Date and Time state, the element is expected to render as an 'inline-block' box depicting a Local Date and Time control.

When the input-number binding applies to an input element whose type attribute is in the Number state, the element is expected to render as an 'inline-block' box depicting a Number control.

These controls are all expected to be about one line high, and about as wide as necessary to show the widest possible value.

10.4.8 The input element as a range control

@namespace url(http://www.w3.org/1999/xhtml);

input[type=range] { binding: input-range; }

When the input-range binding applies to an input element whose type attribute is in the Range state, the element is expected to render as an 'inline-block' box depicting a slider control.

When the control is wider than it is tall (or square), the control is expected to be a horizontal slider, with the lowest value on the right if the 'direction' property on this element has a computed value of 'rtl', and on the left otherwise. When the control is taller than it is wide, it is expected to be a vertical slider, with the lowest value on the bottom.

Predefined suggested values (provided by the list attribute) are expected to be shown as tick marks on the slider, which the slider can snap to.

10.4.9 The input element as a color well

@namespace url(http://www.w3.org/1999/xhtml);

input[type=color] { binding: input-color; }

When the input-color binding applies to an input element whose type attribute is in the Color state, the element is expected to render as an 'inline-block' box depicting a color well, which, when activated, provides the user with a color picker (e.g. a color wheel or color palette) from which the color can be changed.

Predefined suggested values (provided by the list attribute) are expected to be shown in the color picker interface, not on the color well itself.

10.4.10 The input element as a check box and radio button widgets

@namespace url(http://www.w3.org/1999/xhtml);

input[type=checkbox] { binding: input-checkbox; }
input[type=radio] { binding: input-radio; }

When the input-checkbox binding applies to an input element whose type attribute is in the Checkbox state, the element is expected to render as an 'inline-block' box containing a single check box control, with no label.

When the input-radio binding applies to an input element whose type attribute is in the Radio Button state, the element is expected to render as an 'inline-block' box containing a single radio button control, with no label.

10.4.11 The input element as a file upload control

@namespace url(http://www.w3.org/1999/xhtml);

input[type=file] { binding: input-file; }

When the input-file binding applies to an input element whose type attribute is in the File Upload state, the element is expected to render as an 'inline-block' box containing a span of text giving the filename(s) of the selected files, if any, followed by a button that, when activated, provides the user with a file picker from which the selection can be changed.

10.4.12 The input element as a button

@namespace url(http://www.w3.org/1999/xhtml);

input[type=submit], input[type=reset], input[type=button] {
  binding: input-button;
}

When the input-button binding applies to an input element whose type attribute is in the Submit Button, Reset Button, or Button state, the element is expected to render as an 'inline-block' box rendered as a button, about one line high, containing the contents of the element's value attribute, if any, or text derived from the element's type attribute in a user-agent-defined (and probably locale-specific) fashion, if not.

10.4.13 The marquee element

...(Waiting til I've specced the DOM side of this)...

10.4.14 The meter element

@namespace url(http://www.w3.org/1999/xhtml);

meter {
  binding: meter;
}

When the meter binding applies to a meter element, the element is expected to render as an 'inline-block' box with a 'height' of '1em' and a 'width' of '5em', a 'vertical-align' of '-0.2em', and with its contents depicting a gauge.

When the element is wider than it is tall (or square), the depiction is expected to be of a horizontal gauge, with the minimum value on the right if the 'direction' property on this element has a computed value of 'rtl', and on the left otherwise. When the element is taller than it is wide, it is expected to depict a vertical gauge, with the minimum value on the bottom.

User agents are expected to use a presentation consistent with platform conventions for gauges, if any.

Requirements for what must be depicted in the gauge are included in the definition of the meter element.

10.4.15 The progress element

@namespace url(http://www.w3.org/1999/xhtml);

progress {
  binding: progress;
}

When the progress binding applies to a progress element, the element is expected to render as an 'inline-block' box with a 'height' of '1em' and a 'width' of '10em', a 'vertical-align' of '-0.2em', and with its contents depicting a horizontal progress bar, with the start on the right and the end on the left if the 'direction' property on this element has a computed value of 'rtl', and with the start on the left and the end on the right otherwise.

User agents are expected to use a presentation consistent with platform conventions for progress bars. In particular, user agents are expected to use different presentations for determinate and indeterminate progress bars. User agents are also expected to vary the presentation based on the dimensions of the element.

For example, on some platforms for showing indeterminate progress there is an asynchronous progress indicator with square dimensions, which could be used when the element is square, and an indeterminate progress bar, which could be used when the element is wide.

Requirements for how to determine if the progress bar is determinate or indeterminate, and what progress a determinate progress bar is to show, are included in the definition of the progress element.

10.4.16 The select element

@namespace url(http://www.w3.org/1999/xhtml);

select {
  binding: select;
}

When the select binding applies to a select element whose multiple attribute is present, the element is expected to render as a multi-select list box.

When the select binding applies to a select element whose multiple attribute is absent, and the element's size attribute specifies a value greater than 1, the element is expected to render as a single-select list box.

When the element renders as a list box, it is expected to render as an 'inline-block' box whose 'height' is the height necessary to contain as many rows for items as specified by the element's size attribute, or four rows if the attribute is absent, and whose 'width' is the width of the select's labels plus the width of a scrollbar.

When the select binding applies to a select element whose multiple attribute is absent, and the element's size attribute is either absent or specifies either no value (an error), or a value less than or equal to 1, the element is expected to render as a one-line drop down box whose width is the width of the select's labels.

In either case (list box or drop-down box), the element's items are expected to be the element's list of options, with the element's optgroup element children providing headers for groups of options where applicable.

The width of the select's labels is the wider of the width necessary to render the widest optgroup, and the width necessary to render the widest option element in the element's list of options (including its indent, if any).

An optgroup element is expected to be rendered by displaying the element's label attribute.

An option element is expected to be rendered by displaying the element's label, indented under its optgroup element if it has one.

10.4.17 The textarea element

@namespace url(http://www.w3.org/1999/xhtml);

textarea { binding: textarea; }

When the textarea binding applies to a textarea element, the element is expected to render as an 'inline-block' box rendered as a multiline text field.

If the element has a cols attribute, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then the user agent is expected to use the attribute as a presentational hint for the 'width' property on the element, with the value obtained from applying the converting a character width to pixels algorithm to the value of the attribute and then adding the width of a scroll bar.

If the element has a rows attribute, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then the user agent is expected to use the attribute as a presentational hint for the 'height' property on the element, with the value being the specified number of lines, plus the height of a scrollbar.

For historical reasons, if the element has a wrap attribute whose value is an ASCII case-insensitive match for the string "off", then the user agent is expected to not wrap the rendered value; otherwise, the value of the control is expected to be wrapped to the width of the control.

10.4.18 The keygen element

@namespace url(http://www.w3.org/1999/xhtml);

keygen { binding: keygen; }

When the keygen binding applies to a keygen element, the element is expected to render as an 'inline-block' box containing a user interface to configure the key pair to be generated.

10.4.19 The time element

@namespace url(http://www.w3.org/1999/xhtml);

time:empty { binding: time; }

When the time binding applies to a time element, the element is expected to render as if it contained text conveying the date (if known), time (if known), and time zone (if known) represented by the element, in the fashion most convenient for the user.

10.5 Frames and framesets

When an html element's second child element is a frameset element, the user agent is expected to render the frameset element as described below across the surface of the view, instead of applying the usual CSS rendering rules.

When rendering a frameset on a surface, the user agent is expected to use the following layout algorithm:

  1. The cols and rows variables are lists of zero or more pairs consisting of a number and a unit, the unit being one of percentage, relative, and absolute.

    Use the rules for parsing a list of dimensions to parse the value of the element's cols attribute, if there is one. Let cols be the result, or an empty list if there is no such attribute.

    Use the rules for parsing a list of dimensions to parse the value of the element's rows attribute, if there is one. Let rows be the result, or an empty list if there is no such attribute.

  2. For any of the entries in cols or rows that have the number zero and the unit relative, change the entry's number to one.

  3. If cols has no entries, then add a single entry consisting of the value 1 and the unit relative to cols.

    If rows has no entries, then add a single entry consisting of the value 1 and the unit relative to rows.

  4. Invoke the algorithm defined below to convert a list of dimensions to a list of pixel values using cols as the input list, and the width of the surface that the frameset is being rendered into, in CSS pixels, as the input dimension. Let sized cols be the resulting list.

    Invoke the algorithm defined below to convert a list of dimensions to a list of pixel values using rows as the input list, and the height of the surface that the frameset is being rendered into, in CSS pixels, as the input dimension. Let sized rows be the resulting list.

  5. Split the surface into a grid of w×h rectangles, where w is the number of entries in sized cols and h is the number of entries in sized rows.

    Size the columns so that each column in the grid is as many CSS pixels wide as the corresponding entry in the sized cols list.

    Size the rows so that each row in the grid is as many CSS pixels high as the corresponding entry in the sized rows list.

  6. Let children be the list of frame and frameset elements that are children of the frameset element for which the algorithm was invoked.

  7. For each row of the grid of rectangles created in the previous step, from top to bottom, run these substeps:

    1. For each rectangle in the row, from left to right, run these substeps:

      1. If there are any elements left in children, take the first element in the list, and assign it to the rectangle.

        If this is a frameset element, then recurse the entire frameset layout algorithm for that frameset element, with the rectangle as the surface.

        Otherwise, it is a frame element; create a nested browsing context sized to fit the rectangle.

      2. If there are any elements left in children, remove the first element from children.

  8. If the frameset element has a border, draw an outer set of borders around the rectangles, using the element's frame border color.

    For each rectangle, if there is an element assigned to that rectangle, and that element has a border, draw an inner set of borders around that rectangle, using the element's frame border color.

    For each (visible) border that does not abut a rectangle that is assigned a frame element with a noresize attribute (including rectangles in further nested frameset elements), the user agent is expected to allow the user to move the border, resizing the rectangles within, keeping the proportions of any nested frameset grids.

    A frameset or frame element has a border if the following algorithm returns true:

    1. If the element has a frameborder attribute whose value is not the empty string and whose first character is either a U+0031 DIGIT ONE (1), a U+0079 LATIN SMALL LETTER Y, or a U+0059 LATIN CAPITAL LETTER Y, then return true.

    2. Otherwise, if the element has a frameborder attribute, return false.

    3. Otherwise, if the element has a parent element that is a frameset element, then return true if that element has a border, and false if it does not.

    4. Otherwise, return true.

    The frame border color of a frameset or frame element is the color obtained from the following algorithm:

    1. If the element has a bordercolor attribute, and applying the rules for parsing a legacy color value to that attribute's value does not result in an error, then return the color so obtained.

    2. Otherwise, if the element has a parent element that is a frameset element, then the frame border color of that element.

    3. Otherwise, return gray.

The algorithm to convert a list of dimensions to a list of pixel values consists of the following steps:

  1. Let input list be the list of numbers and units passed to the algorithm.

    Let output list be a list of numbers the same length as input list, all zero.

    Entries in output list correspond to the entries in input list that have the same position.

  2. Let input dimension be the size passed to the algorithm.

  3. Let count percentage be the number of entries in input list whose unit is percentage.

    Let total percentage be the sum of all the numbers in input list whose unit is percentage.

    Let count relative be the number of entries in input list whose unit is relative.

    Let total relative be the sum of all the numbers in input list whose unit is relative.

    Let count absolute be the number of entries in input list whose unit is absolute.

    Let total absolute be the sum of all the numbers in input list whose unit is absolute.

    Let remaining space be the value of input dimension.

  4. If total absolute is greater than remaining space, then for each entry in input list whose unit is absolute, set the corresponding value in output list to the number of the entry in input list multiplied by remaining space and divided by total absolute. Then, set remaining space to zero.

    Otherwise, for each entry in input list whose unit is absolute, set the corresponding value in output list to the number of the entry in input list. Then, decrement remaining space by total absolute.

  5. If total percentage multiplied by the input dimension and divided by 100 is greater than remaining space, then for each entry in input list whose unit is percentage, set the corresponding value in output list to the number of the entry in input list multiplied by remaining space and divided by total percentage. Then, set remaining space to zero.

    Otherwise, for each entry in input list whose unit is percentage, set the corresponding value in output list to the number of the entry in input list multiplied by the input dimension and divided by 100. Then, decrement remaining space by total percentage multiplied by the input dimension and divided by 100.

  6. For each entry in input list whose unit is relative, set the corresponding value in output list to the number of the entry in input list multiplied by remaining space and divided by total relative.

  7. Return output list.

User agents working with integer values for frame widths (as opposed to user agents that can lay frames out with subpixel accuracy) are expected to distribute the remainder first the last entry whose unit is relative, then equally (not proportionally) to each entry whose unit is percentage, then equally (not proportionally) to each entry whose unit is absolute, and finally, failing all else, to the last entry.

10.6 Interactive media

10.6.1 Links, forms, and navigation

User agents are expected to allow the user to control aspects of hyperlink activation and form submission, such as which browsing context is to be used for the subsequent navigation.

User agents are expected to allow users to discover the destination of hyperlinks and of forms before triggering their navigation.

User agents are expected to inform the user of whether a hyperlink includes hyperlink auditing, and to let them know at a minimum which domains will be contacted as part of such auditing.

User agents are expected to allow users to navigate browsing contexts to the resources indicated by the cite attributes on q, blockquote, ins, and del elements.

User agents are expected to surface hyperlinks created by link elements in their user interface.

While link elements that create hyperlinks will match the ':link' or ':visited' pseudo-classes, will react to clicks if visible, and so forth, this does not extend to any browser interface constructs that expose those same links. Activating a link through the browser's interface, rather than in the page itself, does not trigger click events and the like.

10.6.2 The mark element

User agents are expected to allow the user to cycle through all the mark elements in a Document. User agents are also expected to bring their existence to the user's attention, even when they are off-screen, e.g. by highlighting portions of the scroll bar that represent portions of the document that contain mark elements.

10.6.3 The title attribute

Given an element (e.g. the element designated by the mouse cursor), if the element, or one of its ancestors, has a title attribute, and the nearest such attribute has a value that is not the empty string, it is expected that the user agent will expose the contents of that attribute as a tooltip.

U+000A LINE FEED (LF) characters are expected to cause line breaks in the tooltip.

User agents are expected to allow the user to request the opportunity to obtain a physical form (or a representation of a physical form) of a Document. For example, selecting the option to print a page or convert it to PDF format.

When the user actually obtains a physical form (or a representation of a physical form) of a Document, the user agent is expected to create a new view with the print media, render the result, and the discard the view.

10.8 Interaction with CSS

Must define that in CSS, tag and attribute names in HTML documents, and class names in quirks mode documents, are case-insensitive, as well as saying which attribute values must be compared case-insensitively.

11 Obsolete features

Authors and documents must not use the features listed in this section. They are documented to enable user agents to support legacy content in an interoperable fashion.

11.1 Self-contained features

11.1.1 The applet element

The applet element is a Java-specific variant of the embed element. In HTML5 the applet element is obsoleted so that all extension frameworks (Java, .NET, Flash, etc) are handled in a consistent manner.

When the sandboxed plugins browsing context flag is set on the browsing context for which the applet element's document is the active document, and when the element has an ancestor object element that is not showing its fallback content, the element must be ignored (it represents nothing).

Otherwise, define how the element works, if supported.

[XXX] interface HTMLDocument {
  readonly attribute HTMLCollection applets;
};

The applets attribute must return an HTMLCollection rooted at the Document node, whose filter matches only applet elements.

11.1.2 The marquee element

...

11.2 Other elements and attributes

The following elements are obsolete and either have no meaning whatsoever or have no requirements beyond those described elsewhere in this specification:


The following attributes are obsolete and either have no meaning whatsoever or have no requirements beyond those described elsewhere in this specification:

11.3 Other DOM APIs

These APIs expose obsolete content attributes.

The [XXX] below is for some annotation meaning "this is just another part of the named interface, and should be treated as if it had been part of the main interface definition".

[XXX] interface HTMLBodyElement {
           attribute DOMString text;
           attribute DOMString bgColor;
           attribute DOMString background;
           attribute DOMString link;
           attribute DOMString vLink;
           attribute DOMString aLink;
};

The text DOM attribute of the body element must reflect the element's text content attribute.

The bgColor DOM attribute of the body element must reflect the element's bgcolor content attribute.

The background DOM attribute of the body element must reflect the element's background content attribute.

The link DOM attribute of the body element must reflect the element's link content attribute.

The aLink DOM attribute of the body element must reflect the element's alink content attribute.

The vLink DOM attribute of the body element must reflect the element's vlink content attribute.

[XXX] interface HTMLDocument {
           attribute DOMString fgColor;
           attribute DOMString bgColor;
           attribute DOMString linkColor;
           attribute DOMString vlinkColor;
           attribute DOMString alinkColor;
};

The fgColor attribute on the Document object must reflect the text attribute on the body element.

The bgColor attribute on the Document object must reflect the bgcolor attribute on the body element.

The linkColor attribute on the Document object must reflect the link attribute on the body element.

The vLinkColor attribute on the Document object must reflect the vlink attribute on the body element.

The aLinkColor attribute on the Document object must reflect the alink attribute on the body element.

11.4 Conformance checkers

To ease the transition from HTML4 Transitional documents to the language defined in this specification, conformance checkers are encouraged to categorize errors that represent usage of old obsolete features that generally have no effect (as defined below) into a separate part of their report, to allow authors to distinguish between likely mistakes and mere vestigial markup.

The following errors may be categorized as described above:

12 Things that you can't do with this specification because they are better handled using other technologies that are further described herein

This section is non-normative.

There are certain features that are not handled by this specification because a client side markup language is not the right level for them, or because the features exist in other languages that can be integrated into this one. This section covers some of the more common requests.

12.1 Localization

If you wish to create localized versions of an HTML application, the best solution is to preprocess the files on the server, and then use HTTP content negotiation to serve the appropriate language.

12.2 Declarative 3D scenes

Embedding 3D imagery into XHTML documents is the domain of X3D, or technologies based on X3D that are namespace-aware.

12.3 Timers

This section is expected to be moved to its own specification in due course. It needs a lot of work to actually make it into a semi-decent spec.

Objects that implement the Window interface must also implement the WindowTimers interface:

[NoInterfaceObject, ImplementedOn=Window] interface WindowTimers {
  // timers
  long setTimeout(in TimeoutHandler handler, in long timeout);
  long setTimeout(in TimeoutHandler handler, in long timeout, arguments...);
  long setTimeout(in DOMString code, in long timeout);
  long setTimeout(in DOMString code, in long timeout, in DOMString language);
  void clearTimeout(in long handle);
  long setInterval(in TimeoutHandler handler, in long timeout);
  long setInterval(in TimeoutHandler handler, in long timeout, arguments...);
  long setInterval(in DOMString code, in long timeout);
  long setInterval(in DOMString code, in long timeout, in DOMString language);
  void clearInterval(in long handle);
};

[Callback=FunctionOnly, NoInterfaceObject]
interface TimeoutHandler {
  void handleEvent([Variadic] in any args);
};

The setTimeout and setInterval methods allow authors to schedule timer-based events.

The setTimeout(handler, timeout[, arguments...]) method takes a reference to a TimeoutHandler object and a length of time in milliseconds. It must return a handle to the timeout created, and then asynchronously wait timeout milliseconds and then queue a task to invoke handleEvent() on the handler object. If any arguments... were provided, they must be passed to the handler as arguments to the handleEvent() function.

Alternatively, setTimeout(code, timeout[, language]) may be used. This variant takes a string instead of a TimeoutHandler object. define the actual requirements for this method, as with the previous one. That string must be parsed using the specified language (defaulting to JavaScript if the third argument is omitted) and executed in the scope of the browsing context associated with the Window object on which the setTimeout() method was invoked.

Need to define language values; need to define that the script corresponding to the code argument is created before the timer is set up, so that the rule on pausing the ticker, below, makes sense.

The setInterval(...) variants must work in the same way as the setTimeout variants except that if timeout is a value greater than zero, the task that invokes the handler or code must be queued again every timeout milliseconds, not just the once.

The clearTimeout() and clearInterval() methods take one integer (the value returned by setTimeout() and setInterval() respectively) and must cancel the specified timeout. When called with a value that does not correspond to an active timeout or interval, the methods must return without doing anything.

For both setTimeout() and setInterval(), the clock upon which the timers are based must only tick while the Document of the global object of their callbacks is fully active.

12.4 Rendering and the DOM

This section is expected to be moved to its own specification in due course. It needs a lot of work to actually make it into a semi-decent spec.

Any object implement the AbstractView interface must also implement the MediaModeAbstractView interface.

[NoInterfaceObject, ImplementedOn=AbstractView] interface MediaModeAbstractView {
  readonly attribute DOMString mediaMode;
};

The mediaMode attribute on objects implementing the MediaModeAbstractView interface must return the string that represents the canvas' current rendering mode (screen, print, etc). This is a lowercase string, as defined by the CSS specification. [CSS21]

Some user agents may support multiple media, in which case there will exist multiple objects implementing the AbstractView interface. Only the default view implements the Window interface. The other views can be reached using the view attribute of the UIEvent interface, during event propagation. There is no way currently to enumerate all the views.

Index

This section is non-normative.

List of elements

List of attributes

List of reflecting DOM attributes and their corresponding content attributes

List of interfaces

List of events

References

This section will be written in a future draft.

Acknowledgements

Thanks to Aankhen, Aaron Boodman, Aaron Leventhal, Adam Barth, Adam Roben, Addison Phillips, Adele Peterson, Adrian Sutton, Agustín Fernández, Ajai Tirumali, Alan Plum, Alastair Campbell, Alex Nicolaou, Alexander J. Vincent, Alexey Feldgendler, Алексей Проскуряков (Alexey Proskuryakov), Alexis Deveria, Allan Clements, Anders Carlsson, Andreas, Andrew Clover, Andrew Gove, Andrew Sidwell, Andrew Smith, Andy Heydon, Anne van Kesteren, Anthony Boyd, Anthony Bryan, Anthony Hickson, Anthony Ricaud, Antti Koivisto, Arphen Lin, Asbjørn Ulsberg, Ashley Sheridan, Aurelien Levy, Ave Wrigley, Ben Boyle, Ben Godfrey, Ben Meadowcroft, Ben Millard, Benjamin Hawkes-Lewis, Bert Bos, Bijan Parsia, Bill Mason, Bill McCoy, Billy Wong, Björn Höhrmann, Blake Frantz, Boris Zbarsky, Brad Fults, Brad Neuberg, Brady Eidson, Brendan Eich, Brenton Simpson, Brett Wilson, Brian Campbell, Brian Korver, Brian Ryner, Brian Smith, Brian Wilson, Bruce Lawson, Bruce Miller, C. Williams, Cameron McCormack, Cao Yipeng, Carlos Perelló Marín, Chao Cai, 윤석찬 (Channy Yun), Charl van Niekerk, Charles Iliya Krempeaux, Charles McCathieNevile, Chris Morris, Chris Pearce, Christian Biesinger, Christian Johansen, Christian Schmidt, Christopher Aillon, Chriswa, Cole Robison, Colin Fine, Collin Jackson, Corprew Reed, Craig Cockburn, Csaba Gabor, Daniel Barclay, Daniel Bratell, Daniel Brooks, Daniel Brumbaugh Keeney, Daniel Davis, Daniel Glazman, Daniel Peng, Daniel Schattenkirchner, Daniel Spång, Daniel Steinberg, Danny Sullivan, Darin Adler, Darin Fisher, Dave Camp, Dave Hodder, Dave Singer, Dave Townsend, David Baron, David Bloom, David Carlisle, David E. Cleary, David Flanagan, David Håsäther, David Hyatt, David Matja, David Smith, David Woolley, DeWitt Clinton, Dean Edridge, Dean Edwards, Debi Orton, Derek Featherstone, Dimitri Glazkov, dolphinling, Doron Rosenberg, Doug Kramer, Drew Wilson, Edmund Lai, Edward O'Connor, Edward Welbourne, Edward Z. Yang, Eira Monstad, Elliotte Harold, Eric Carlson, Eric Law, Eric Rescorla, Erik Arvidsson, Evan Martin, Evan Prodromou, fantasai, Felix Sasaki, Francesco Schwarz, Franck 'Shift' Quélain, Garrett Smith, Geoffrey Garen, Geoffrey Sneddon, George Lund, Greg Botten, Greg Houston, Grey, Gytis Jakutonis, Håkon Wium Lie, Hallvord Reiar Michaelsen Steen, Hans S. Tømmerhalt, Henri Sivonen, Henrik Lied, Henry Mason, Hugh Winkler, Ian Bicking, Ignacio Javier, Ivan Enderlin, Ivo Emanuel Gonçalves, J. King, Jacques Distler, James Craig, James Graham, James Justin Harrell, James M Snell, James Perrett, Jan-Klaas Kollhof, Jason Kersey, Jason Lustig, Jason White, Jasper Bryant-Greene, Jed Hartman, Jeff Cutsinger, Jeff Schiller, Jeff Walden, Jens Bannmann, Jens Fendler, Jens Lindström, Jens Meiert, Jeroen van der Meer, Jim Jewett, Jim Ley, Jim Meehan, Jjgod Jiang, Joe Clark, Joe Gregorio, Joel Spolsky, Johan Herland, John Boyer, John Bussjaeger, John Fallows, John Harding, John Keiser, John-Mark Bell, Johnny Stenback, Jon Ferraiolo, Jon Gibbins, Jon Perlow, Jonas Sicking, Jonathan Worent, Jonny Axelsson, Jorgen Horstink, Jorunn Danielsen Newth, Joseph Kesselman, Josh Aas, Josh Levenberg, Joshua Randall, Jukka K. Korpela, Jules Clément-Ripoche, Julian Reschke, Justin Sinclair, Kai Hendry, Kartikaya Gupta, Kristof Zelechovski, 黒澤剛志 (KUROSAWA Takeshi), Kyle Hofmann, Léonard Bouchet, Lachlan Hunt, Larry Page, Lars Gunther, Lars Solberg, Laura L. Carlson, Laura Wisewell, Laurens Holst, Lee Kowalkowski, Leif Halvard Silli, Lenny Domnitser, Leons Petrazickis, Logan, Loune, Maciej Stachowiak, Magnus Kristiansen, Maik Merten, Malcolm Rowe, Mark Birbeck, Mark Miller, Mark Nottingham, Mark Rowe, Mark Schenk, Mark Wilton-Jones, Martijn Wargers, Martin Atkins, Martin Dürst, Martin Honnen, Martin Kutschker, Masataka Yakura, Mathieu Henri, Matt Wright, Matthew Gregan, Matthew Mastracci, Matthew Raymond, Matthew Thomas, Mattias Waldau, Max Romantschuk, Menno van Slooten, Micah Dubinko, Michael 'Ratt' Iannarelli, Michael A. Nachbaur, Michael A. Puls II, Michael Carter, Michael Daskalov, Michael Enright, Michael Gratton, Michael Nordman, Michael Powers, Michael(tm) Smith, Michel Fortin, Michiel van der Blonk, Mihai Şucan, Mike Brown, Mike Dierken, Mike Dixon, Mike Schinkel, Mike Shaver, Mikko Rantalainen, Mohamed Zergaoui, Neil Deakin, Neil Rashbrook, Neil Soiffer, Nicholas Shanks, Nicolas Gallagher, Ojan Vafai, Olaf Hoffmann, Olav Junker Kjær, Oliver Hunt, Olli Pettay, Patrick H. Lauke, Paul Norman, Peter Karlsson, Peter Kasting, Peter Stark, Peter-Paul Koch, Philip Jägenstedt, Philip Taylor, Philip TAYLOR, Rachid Finge, Rajas Moonka, Ralf Stoltze, Ralph Giles, Raphael Champeimont, Rene Saarsoo, Rene Stach, Rich Doughty, Richard Ishida, Rigo Wenning, Rikkert Koppes, Rimantas Liubertas, Robert Blaut, Robert O'Callahan, Robert Sayre, Roman Ivanov, Ryan King, S. Mike Dierken, Sam Kuper, Sam Ruby, Sam Weinig, Sander van Lambalgen, Scott Hess, Sean Fraser, Sean Hogen, Sean Knapp, Sebastian Schnitzenbaumer, Shanti Rao, Shaun Inman, Shiki Okasaka, Sierk Bornemann, Sigbjørn Vik, Silvia Pfeiffer, Simon Montagu, Simon Pieters, Stefan Haustein, Steffen Meschkat, Stephen Ma, Steve Faulkner, Steve Runyon, Steven Garrity, Stewart Brodie, Stuart Ballard, Stuart Parmenter, Subramanian Peruvemba, Sunava Dutta, Susan Borgrink, Susan Lesch, Tantek Çelik, Ted Mielczarek, Terrence Wood, Thomas Broyer, Thomas O'Connor, Tim Altman, Tim Johansson, Todd Moody, Tom Pike, Tommy Thorsen, Travis Leithead, Tyler Close, Vladimir Vukićević, voracity, Wakaba, Wayne Pollock, Wellington Fernando de Macedo, Will Levine, William Swanson, Wladimir Palant, Wolfram Kriesing, Yi-An Huang, Yngve Nysaeter Pettersen, Zhenbin Xu, and Øistein E. Andersen, for their useful comments, both large and small, that have led to changes to this specification over the years.

Thanks also to everyone who has ever posted about HTML5 to their blogs, public mailing lists, or forums, including the W3C public-html list and the various WHATWG lists.

Special thanks to Richard Williamson for creating the first implementation of canvas in Safari, from which the canvas feature was designed.

Special thanks also to the Microsoft employees who first implemented the event-based drag-and-drop mechanism, contenteditable, and other features first widely deployed by the Windows Internet Explorer browser.

Special thanks and $10,000 to David Hyatt who came up with a broken implementation of the adoption agency algorithm that the editor had to reverse engineer and fix before using it in the parsing section.

Thanks to the many sources that provided inspiration for the examples used in the specification.

Thanks also to the Microsoft blogging community for some ideas, to the attendees of the W3C Workshop on Web Applications and Compound Documents for inspiration, to the #mrt crew, the #mrt.no crew, and the #whatwg crew, and to Pillar and Hedral for their ideas and support.