HTML 5

Abstract

This specification introduces features to HTML and the DOM that ease the authoring of Web-based applications. Additions include the context menus, a direct-mode graphics canvas, inline popup windows, and server-sent events.

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.

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! There are also some spec-wide issues that have not yet been addressed: case-sensitivity is a very poorly handled topic right now, and the firing of events needs to be unified (right now some bubble, some don't, they all use different text to fire events, etc). It would also be nice to unify the rules on downloading content when attributes change (e.g. src attributes) - should they initiate downloads when the element immediately, is inserted in the document, when active scripts end, etc. This matters e.g. if an attribute is set twice in a row (does it hit the network twice).

Table of contents

• 1. Introduction
  • 1.1. Scope
    • 1.1.1. Relationship to HTML 4.01, XHTML 1.1, DOM2 HTML
    • 1.1.2. Relationship to XHTML2
    • 1.1.3. Relationship to XUL, Flash, Silverlight, and other proprietary UI languages
  • 1.2. Structure of this specification
    • 1.2.1. How to read this specification
  • 1.3. Conformance requirements
    • 1.3.1. Common conformance requirements for APIs exposed to JavaScript
    • 1.3.2. Dependencies
    • 1.3.3. Features defined in other specifications
  • 1.4. Terminology
    • 1.4.1. HTML vs XHTML
• 2. The Document Object Model
  • 2.1. Documents
    • 2.1.1. Security
    • 2.1.2. Resource metadata management
  • 2.2. Elements
    • 2.2.1. Reflecting content attributes in DOM attributes
  • 2.3. Common DOM interfaces
    • 2.3.1. Collections
      • 2.3.1.1. HTMLCollection
      • 2.3.1.2. HTMLFormControlsCollection
      • 2.3.1.3. HTMLOptionsCollection
    • 2.3.2. DOMTokenList
    • 2.3.3. DOM feature strings
  • 2.4. DOM tree accessors
  • 2.5. Dynamic markup insertion
    • 2.5.1. Controlling the input stream
    • 2.5.2. Dynamic markup insertion in HTML
    • 2.5.3. Dynamic markup insertion in XML
  • 2.6. APIs in HTML documents
• 3. Semantics and structure of HTML elements
  • 3.1. Introduction
  • 3.2. Common microsyntaxes
    • 3.2.1. Common parser idioms
    • 3.2.2. Boolean attributes
    • 3.2.3. Numbers
      • 3.2.3.1. Unsigned integers
      • 3.2.3.2. Signed integers
      • 3.2.3.3. Real numbers
      • 3.2.3.4. Ratios
      • 3.2.3.5. Percentages and dimensions
      • 3.2.3.6. Lists of integers
    • 3.2.4. Dates and times
      • 3.2.4.1. Specific moments in time
      • 3.2.4.2. Vaguer moments in time
    • 3.2.5. Time offsets
    • 3.2.6. Tokens
    • 3.2.7. Keywords and enumerated attributes
    • 3.2.8. References
  • 3.3. Documents and document fragments
    • 3.3.1. Semantics
    • 3.3.2. Structure
    • 3.3.3. Kinds of content
      • 3.3.3.1. Metadata content
      • 3.3.3.2. Prose content
      • 3.3.3.3. Sectioning content
      • 3.3.3.4. Heading content
      • 3.3.3.5. Phrasing content
      • 3.3.3.6. Embedded content
      • 3.3.3.7. Interactive content
    • 3.3.4. Transparent content models
    • 3.3.5. Paragraphs
  • 3.4. Global attributes
    • 3.4.1. The id attribute
    • 3.4.2. The title attribute
    • 3.4.3. The lang (HTML only) and xml:lang (XML only) attributes
    • 3.4.4. The dir attribute
    • 3.4.5. The class attribute
    • 3.4.6. The irrelevant attribute
  • 3.5. Interaction
    • 3.5.1. Activation
    • 3.5.2. Focus
      • 3.5.2.1. Focus management
      • 3.5.2.2. Sequential focus navigation
    • 3.5.3. Scrolling elements into view
  • 3.6. The root element
    • 3.6.1. The html element
  • 3.7. Document metadata
    • 3.7.1. The head element
    • 3.7.2. The title element
    • 3.7.3. The base element
    • 3.7.4. The link element
    • 3.7.5. The meta element
      • 3.7.5.1. Standard metadata names
      • 3.7.5.2. Other metadata names
      • 3.7.5.3. Pragma directives
      • 3.7.5.4. Specifying the document's character encoding
    • 3.7.6. The style element
    • 3.7.7. Styling
  • 3.8. Sections
    • 3.8.1. The body element
    • 3.8.2. The section element
    • 3.8.3. The nav element
    • 3.8.4. The article element
    • 3.8.5. The blockquote element
    • 3.8.6. The aside element
    • 3.8.7. The h1, h2, h3, h4, h5, and h6 elements
    • 3.8.8. The header element
    • 3.8.9. The footer element
    • 3.8.10. The address element
    • 3.8.11. Headings and sections
      • 3.8.11.1. Creating an outline
      • 3.8.11.2. Determining which heading and section applies to a particular node
      • 3.8.11.3. Distinguishing site-wide headers from page headers
  • 3.9. Prose
    • 3.9.1. The p element
    • 3.9.2. The hr element
    • 3.9.3. The br element
    • 3.9.4. The dialog element
  • 3.10. Preformatted text
    • 3.10.1. The pre element
  • 3.11. Lists
    • 3.11.1. The ol element
    • 3.11.2. The ul element
    • 3.11.3. The li element
    • 3.11.4. The dl element
    • 3.11.5. The dt element
    • 3.11.6. The dd element
  • 3.12. Phrase elements
    • 3.12.1. The a element
    • 3.12.2. The q element
    • 3.12.3. The cite element
    • 3.12.4. The em element
    • 3.12.5. The strong element
    • 3.12.6. The small element
    • 3.12.7. The m element
    • 3.12.8. The dfn element
    • 3.12.9. The abbr element
    • 3.12.10. The time element
    • 3.12.11. The progress element
    • 3.12.12. The meter element
    • 3.12.13. The code element
    • 3.12.14. The var element
    • 3.12.15. The samp element
    • 3.12.16. The kbd element
    • 3.12.17. The sub and sup elements
    • 3.12.18. The span element
    • 3.12.19. The i element
    • 3.12.20. The b element
    • 3.12.21. The bdo element
  • 3.13. Edits
    • 3.13.1. The ins element
    • 3.13.2. The del element
    • 3.13.3. Attributes common to ins and del elements
  • 3.14. Embedded content
    • 3.14.1. The figure element
    • 3.14.2. The img element
    • 3.14.3. The iframe element
    • 3.14.4. The embed element
    • 3.14.5. The object element
    • 3.14.6. The param element
    • 3.14.7. The video element
      • 3.14.7.1. Video and audio codecs for video elements
    • 3.14.8. The audio element
      • 3.14.8.1. Audio codecs for audio elements
    • 3.14.9. Media elements
      • 3.14.9.1. Error codes
      • 3.14.9.2. Location of the media resource
      • 3.14.9.3. Network states
      • 3.14.9.4. Loading the media resource
      • 3.14.9.5. Offsets into the media resource
      • 3.14.9.6. The ready states
      • 3.14.9.7. Playing the media resource
      • 3.14.9.8. Seeking
      • 3.14.9.9. Cue ranges
      • 3.14.9.10. User interface
      • 3.14.9.11. Time range
      • 3.14.9.12. Event summary
      • 3.14.9.13. Security and privacy considerations
    • 3.14.10. The source element
    • 3.14.11. The canvas element
      • 3.14.11.1. The 2D context
        • 3.14.11.1.1. The canvas state
        • 3.14.11.1.2. Transformations
        • 3.14.11.1.3. Compositing
        • 3.14.11.1.4. Colors and styles
        • 3.14.11.1.5. Line styles
        • 3.14.11.1.6. Shadows
        • 3.14.11.1.7. Simple shapes (rectangles)
        • 3.14.11.1.8. Complex shapes (paths)
        • 3.14.11.1.9. Images
        • 3.14.11.1.10. Pixel manipulation
        • 3.14.11.1.11. Drawing model
    • 3.14.12. The map element
    • 3.14.13. The area element
    • 3.14.14. Image maps
    • 3.14.15. Dimension attributes
  • 3.15. Tabular data
    • 3.15.1. The table element
    • 3.15.2. The caption element
    • 3.15.3. The colgroup element
    • 3.15.4. The col element
    • 3.15.5. The tbody element
    • 3.15.6. The thead element
    • 3.15.7. The tfoot element
    • 3.15.8. The tr element
    • 3.15.9. The td element
    • 3.15.10. The th element
    • 3.15.11. Processing model
      • 3.15.11.1. Forming a table
      • 3.15.11.2. Forming relationships between data cells and header cells
  • 3.16. Forms
    • 3.16.1. The form element
    • 3.16.2. The fieldset element
    • 3.16.3. The input element
    • 3.16.4. The button element
    • 3.16.5. The label element
    • 3.16.6. The select element
    • 3.16.7. The datalist element
    • 3.16.8. The optgroup element
    • 3.16.9. The option element
    • 3.16.10. The textarea element
    • 3.16.11. The output element
    • 3.16.12. Processing model
      • 3.16.12.1. Form submission
  • 3.17. Scripting
    • 3.17.1. The script element
      • 3.17.1.1. Scripting languages
    • 3.17.2. The noscript element
    • 3.17.3. The event-source element
  • 3.18. Interactive elements
    • 3.18.1. The details element
    • 3.18.2. The datagrid element
      • 3.18.2.1. The datagrid data model
      • 3.18.2.2. How rows are identified
      • 3.18.2.3. The data provider interface
      • 3.18.2.4. The default data provider
        • 3.18.2.4.1. Common default data provider method definitions for cells
      • 3.18.2.5. Populating the datagrid element
      • 3.18.2.6. Updating the datagrid
      • 3.18.2.7. Requirements for interactive user agents
      • 3.18.2.8. The selection
      • 3.18.2.9. Columns and captions
    • 3.18.3. The command element
    • 3.18.4. The menu element
      • 3.18.4.1. Introduction
      • 3.18.4.2. Building menus and tool bars
      • 3.18.4.3. Context menus
      • 3.18.4.4. Toolbars
    • 3.18.5. Commands
      • 3.18.5.1. Using the a element to define a command
      • 3.18.5.2. Using the button element to define a command
      • 3.18.5.3. Using the input element to define a command
      • 3.18.5.4. Using the option element to define a command
      • 3.18.5.5. Using the command element to define a command
  • 3.19. Data Templates
    • 3.19.1. Introduction
    • 3.19.2. The datatemplate element
    • 3.19.3. The rule element
    • 3.19.4. The nest element
    • 3.19.5. Global attributes for data templates
    • 3.19.6. Processing model
      • 3.19.6.1. The originalContent DOM attribute
      • 3.19.6.2. The template attribute
      • 3.19.6.3. The ref attribute
      • 3.19.6.4. The NodeDataTemplate interface
      • 3.19.6.5. Mutations
      • 3.19.6.6. Updating the generated content
  • 3.20. Miscellaneous elements
    • 3.20.1. The legend element
    • 3.20.2. The div element
• 4. Web browsers
  • 4.1. Browsing contexts
    • 4.1.1. Nested browsing contexts
    • 4.1.2. Auxiliary browsing contexts
    • 4.1.3. Secondary browsing contexts
    • 4.1.4. Threads
    • 4.1.5. Browsing context names
  • 4.2. The default view
    • 4.2.1. Security
    • 4.2.2. Constructors
    • 4.2.3. APIs for creating and navigating browsing contexts by name
    • 4.2.4. Accessing other browsing contexts
  • 4.3. Scripting
    • 4.3.1. Running executable code
    • 4.3.2. Origin
    • 4.3.3. Unscripted same-origin checks
    • 4.3.4. Security exceptions
    • 4.3.5. The javascript: protocol
    • 4.3.6. Events
      • 4.3.6.1. Event handler attributes
      • 4.3.6.2. Event firing
      • 4.3.6.3. Events and the Window object
      • 4.3.6.4. Runtime script errors
  • 4.4. User prompts
  • 4.5. Browser state
    • 4.5.1. Custom protocol and content handlers
      • 4.5.1.1. Security and privacy
      • 4.5.1.2. Sample user interface
  • 4.6. Offline Web applications
    • 4.6.1. Introduction
    • 4.6.2. Application caches
    • 4.6.3. The cache manifest syntax
      • 4.6.3.1. Writing cache manifests
      • 4.6.3.2. Parsing cache manifests
    • 4.6.4. Updating an application cache
    • 4.6.5. Processing model
      • 4.6.5.1. Changes to the networking model
    • 4.6.6. Application cache API
    • 4.6.7. Browser state
  • 4.7. Session history and navigation
    • 4.7.1. The session history of browsing contexts
    • 4.7.2. The History interface
    • 4.7.3. Activating state objects
    • 4.7.4. The Location interface
      • 4.7.4.1. Security
    • 4.7.5. Implementation notes for session history
  • 4.8. Navigating across documents
    • 4.8.1. Page load processing model for HTML files
    • 4.8.2. Page load processing model for XML files
    • 4.8.3. Page load processing model for text files
    • 4.8.4. Page load processing model for images
    • 4.8.5. Page load processing model for content that uses plugins
    • 4.8.6. Page load processing model for inline content that doesn't have a DOM
    • 4.8.7. Navigating to a fragment identifier
  • 4.9. Determining the type of a new resource in a browsing context
    • 4.9.1. Content-Type sniffing: text or binary
    • 4.9.2. Content-Type sniffing: unknown type
    • 4.9.3. Content-Type sniffing: image
    • 4.9.4. Content-Type sniffing: feed or HTML
    • 4.9.5. Content-Type metadata
  • 4.10. Client-side session and persistent storage of name/value pairs
    • 4.10.1. Introduction
    • 4.10.2. The Storage interface
    • 4.10.3. The sessionStorage attribute
    • 4.10.4. The globalStorage attribute
    • 4.10.5. The storage event
    • 4.10.6. Miscellaneous implementation requirements for storage areas
      • 4.10.6.1. Disk space
      • 4.10.6.2. Threads
    • 4.10.7. Security and privacy
      • 4.10.7.1. User tracking
      • 4.10.7.2. Cookie resurrection
      • 4.10.7.3. DNS spoofing attacks
      • 4.10.7.4. Cross-directory attacks
      • 4.10.7.5. Implementation risks
  • 4.11. Client-side database storage
    • 4.11.1. Introduction
    • 4.11.2. Databases
    • 4.11.3. Executing SQL statements
    • 4.11.4. Database query results
    • 4.11.5. Errors
    • 4.11.6. Processing model
    • 4.11.7. Privacy
    • 4.11.8. Security
      • 4.11.8.1. User agents
      • 4.11.8.2. SQL injection
  • 4.12. Links
    • 4.12.1. Hyperlink elements
    • 4.12.2. Following hyperlinks
      • 4.12.2.1. Hyperlink auditing
    • 4.12.3. Link types
      • 4.12.3.1. Link type "alternate"
      • 4.12.3.2. Link type "archives"
      • 4.12.3.3. Link type "author"
      • 4.12.3.4. Link type "bookmark"
      • 4.12.3.5. Link type "contact"
      • 4.12.3.6. Link type "external"
      • 4.12.3.7. Link type "feed"
      • 4.12.3.8. Link type "help"
      • 4.12.3.9. Link type "icon"
      • 4.12.3.10. Link type "license"
      • 4.12.3.11. Link type "nofollow"
      • 4.12.3.12. Link type "noreferrer"
      • 4.12.3.13. Link type "pingback"
      • 4.12.3.14. Link type "prefetch"
      • 4.12.3.15. Link type "search"
      • 4.12.3.16. Link type "stylesheet"
      • 4.12.3.17. Link type "sidebar"
      • 4.12.3.18. Link type "tag"
      • 4.12.3.19. Hierarchical link types
        • 4.12.3.19.1. Link type "index"
        • 4.12.3.19.2. Link type "up"
      • 4.12.3.20. Sequential link types
        • 4.12.3.20.1. Link type "first"
        • 4.12.3.20.2. Link type "last"
        • 4.12.3.20.3. Link type "next"
        • 4.12.3.20.4. Link type "prev"
      • 4.12.3.21. Other link types
  • 4.13. Interfaces for URI manipulation
• 5. Editing
  • 5.1. Introduction
  • 5.2. The contenteditable attribute
    • 5.2.1. User editing actions
    • 5.2.2. Making entire documents editable
  • 5.3. Drag and drop
    • 5.3.1. The DragEvent and DataTransfer interfaces
    • 5.3.2. Events fired during a drag-and-drop action
    • 5.3.3. Drag-and-drop processing model
      • 5.3.3.1. When the drag-and-drop operation starts or ends in another document
      • 5.3.3.2. When the drag-and-drop operation starts or ends in another application
    • 5.3.4. The draggable attribute
    • 5.3.5. Copy and paste
      • 5.3.5.1. Copy to clipboard
      • 5.3.5.2. Cut to clipboard
      • 5.3.5.3. Paste from clipboard
      • 5.3.5.4. Paste from selection
    • 5.3.6. Security risks in the drag-and-drop model
  • 5.4. Undo history
    • 5.4.1. The UndoManager interface
    • 5.4.2. Undo: moving back in the undo transaction history
    • 5.4.3. Redo: moving forward in the undo transaction history
    • 5.4.4. The UndoManagerEvent interface and the undo and redo events
    • 5.4.5. Implementation notes
  • 5.5. Command APIs
  • 5.6. The text selection APIs
    • 5.6.1. APIs for the browsing context selection
    • 5.6.2. APIs for the text field selections
• 6. Communication
  • 6.1. Event definitions
  • 6.2. Server-sent DOM events
    • 6.2.1. The RemoteEventTarget interface
    • 6.2.2. Connecting to an event stream
    • 6.2.3. Parsing an event stream
    • 6.2.4. Interpreting an event stream
    • 6.2.5. Notes
  • 6.3. Network connections
    • 6.3.1. Introduction
    • 6.3.2. The Connection interface
    • 6.3.3. Connection Events
    • 6.3.4. TCP connections
    • 6.3.5. Broadcast connections
      • 6.3.5.1. Broadcasting over TCP/IP
      • 6.3.5.2. Broadcasting over Bluetooth
      • 6.3.5.3. Broadcasting over IrDA
    • 6.3.6. Peer-to-peer connections
      • 6.3.6.1. Peer-to-peer connections over TCP/IP
      • 6.3.6.2. Peer-to-peer connections over Bluetooth
      • 6.3.6.3. Peer-to-peer connections over IrDA
    • 6.3.7. The common protocol for TCP-based connections
      • 6.3.7.1. Clients connecting over TCP
      • 6.3.7.2. Servers accepting connections over TCP
      • 6.3.7.3. Sending and receiving data over TCP
    • 6.3.8. Security
    • 6.3.9. Relationship to other standards
  • 6.4. Cross-document messaging
    • 6.4.1. Processing model
• 7. Repetition templates
• 8. The HTML syntax
  • 8.1. Writing HTML documents
    • 8.1.1. The DOCTYPE
    • 8.1.2. Elements
      • 8.1.2.1. Start tags
      • 8.1.2.2. End tags
      • 8.1.2.3. Attributes
      • 8.1.2.4. Optional tags
      • 8.1.2.5. Restrictions on content models
      • 8.1.2.6. Restrictions on the contents of CDATA and RCDATA elements
    • 8.1.3. Text
      • 8.1.3.1. Newlines
    • 8.1.4. Character entity references
    • 8.1.5. Comments
  • 8.2. Parsing HTML documents
    • 8.2.1. Overview of the parsing model
    • 8.2.2. The input stream
      • 8.2.2.1. Determining the character encoding
      • 8.2.2.2. Character encoding requirements
      • 8.2.2.3. Preprocessing the input stream
      • 8.2.2.4. Changing the encoding while parsing
    • 8.2.3. Tokenisation
      • 8.2.3.1. Tokenising entities
    • 8.2.4. Tree construction
      • 8.2.4.1. The initial phase
      • 8.2.4.2. The root element phase
      • 8.2.4.3. The main phase
        • 8.2.4.3.1. The stack of open elements
        • 8.2.4.3.2. The list of active formatting elements
        • 8.2.4.3.3. Creating and inserting HTML elements
        • 8.2.4.3.4. Closing elements that have implied end tags
        • 8.2.4.3.5. The element pointers
        • 8.2.4.3.6. The insertion mode
        • 8.2.4.3.7. How to handle tokens in the main phase
      • 8.2.4.4. The trailing end phase
    • 8.2.5. The End
  • 8.3. Namespaces
  • 8.4. Serialising HTML fragments
  • 8.5. Parsing HTML fragments
  • 8.6. Entities
• 9. WYSIWYG editors
  • 9.1. Presentational markup
    • 9.1.1. WYSIWYG signature
    • 9.1.2. The font element
• 10. Rendering
  • 10.1. Rendering and the DOM
  • 10.2. Rendering and menus/toolbars
    • 10.2.1. The 'icon' property
• 11. Things that you can't do with this specification because they are better handled using other technologies that are further described herein
  • 11.1. Localisation
  • 11.2. Declarative 2D vector graphics and animation
  • 11.3. Declarative 3D scenes
  • 11.4. Timers
  • 11.5. Events
• References
• Acknowledgements

1. Introduction

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.

1.1. 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 addressing presentation concerns (although default rendering rules for Web browsers are included at the end of this specification).

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.

For sophisticated cross-platform applications, there already exist several proprietary solutions (such as Mozilla's XUL and Macromedia's Flash). These solutions are evolving faster than any standards process could follow, and the requirements are evolving even faster. These systems are also significantly more complicated to specify, and are orders of magnitude more difficult to achieve interoperability with, than the solutions described in this document. Platform-specific solutions for such sophisticated applications (for example the MacOS X Core APIs) are even further ahead.

1.1.1. Relationship to HTML 4.01, XHTML 1.1, DOM2 HTML

This section is non-normative.

This specification represents a new version of HTML4 and XHTML1, along with a new version of the associated DOM2 HTML API. Migration from HTML4 or XHTML1 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.

This specification will eventually supplant Web Forms 2.0 as well. [WF2]

1.1.2. Relationship to XHTML2

This section is non-normative.

XHTML2 [XHTML2] defines a new HTML vocabulary with better 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.

However, it lacks elements to express the semantics of many of the non-document types of content often seen on the Web. For instance, forum sites, auction sites, search engines, online shops, and the like, do not fit the document metaphor well, and are not covered by XHTML2.

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

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

1.1.3. Relationship to XUL, Flash, Silverlight, and other proprietary UI languages

This section is non-normative.

This specification is independent of the various proprietary UI languages that various vendors provide. As an open, vender-neutral language, HTML provides for a solution to the same problems without the risk of vendor lock-in.

1.2. Structure of this specification

This section is non-normative.

This specification is divided into the following important sections:

The DOM

The DOM, or Document Object Model, provides a base for the rest of the specification.

The Semantics

Documents are built from elements. These elements form a tree using the DOM. Each element also has a predefined meaning, which is explained in this section. User agent requirements for how to handle each element are also given, along with rules for authors on how to use the element.

Browsing Contexts

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.

APIs

The Editing APIs: HTML documents can provide a number of mechanisms for users to 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.

Repetition Templates: A mechanism to support repeating sections in forms.

The Language Syntax

All of these features would be for naught if they couldn't be represented in a serialised 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 shims for WYSIWYG editors, rendering rules for Web browsers, and listing areas that are out of scope for this specification.

1.2.1. 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.

1.3. 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", "SHALL", "SHALL NOT", "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 an XSLT transformation sheet (assuming the UA 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 labelled as text/html as described in this specification, so that users can interact with them.

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) 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. 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 do not have to check that blockquote elements only contain quoted material).

Conformance checkers must check that the input document conforms when scripting is disabled, and should also check that the input document conforms when scripting is enabled. (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 tools 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 errorneous 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, and this specification makes certain concessions to WYSIWYG editors.

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 behaviour. The former category of requirements are requirements on documents and authoring tools. 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]

Such XML documents may contain a DOCTYPE if desired, but this is not required to conform to this specification.

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 entities for characters in XHTML documents is unsafe (except for <, >, &, " and '). For interoperability, authors are advised to avoid optional features of XML.

HTML documents, if they are served over the wire (e.g. by HTTP) must be labelled 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.

1.3.1. Common conformance requirements for APIs exposed to JavaScript

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 other 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 other specified, if a DOM attribute that is a signed numeric type is assigned a negative value, a NOT_SUPPORTED_ERR exception must be raised.

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

Unless other specified, if a method is expecting, as one of its arguments, as defined by its IDL definition, an object implementing a particular interface X, and the argument passed is an object whose [[Class]] property is neither that interface X, nor the name of an interface Y where this specification requires that all objects implementing interface Y also implement interface X, nor the name of an interface that inherits from the expected interface X, then a TYPE_MISMATCH_ERR exception must be raised.

Anything else? Passing the wrong type of object, maybe? Implied conversions to int/float?

1.3.2. 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 serialisation with namespaces. [XML] [XMLNAMES]

XML Base

User agents must follow the rules given by XML Base to resolve relative URIs in HTML and XHTML fragments. That is the mechanism used in this specification for resolving relative URIs in DOM trees. [XMLBASE]

It is possible for xml:base attributes to be present even in HTML fragments, as such attributes can be added dynamically using script.

DOM

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]

ECMAScript

Implementations that use ECMAScript to implement the APIs defined in this specification must implement them in a manner consistent with the ECMAScript Bindings for DOM Specifications specification, as this specification uses that specification's terminology. [EBFD]

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, ECMAScript 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.

1.3.3. Features defined in other specifications

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

Should textContent be defined differently for dir="" and <bdo>? Should we come up with an alternative to textContent that handles those and other things, like alt=""?

The interface DOMTimeStamp is defined in DOM3 Core. [DOM3CORE]

The term activation behavior is used as defined in the DOM3 Events specification. [DOM3EVENTS] At the time of writing, DOM3 Events hadn't yet been updated to define that phrase.

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?rev=1.35&content-type=text/html;%20charset=utf-8

Certain features are defined in terms of CSS <color> values. When the CSS value currentColor is specified in this context, 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. [CSS3COLOR]

If a canvas gradient's addColorStop() method is called with the currentColor keyword as the color, then the computed value of the 'color' property on the canvas element is the one that is used.

1.4. 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 ECMAScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.

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).

The term HTML documents is sometimes used in contrast with XML documents to mean specifically 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 readability, the term URI is used to refer to both ASCII URIs and Unicode IRIs, as those terms are defined by RFC 3986 and RFC 3987 respectively. On the rare occasions where IRIs are not allowed but ASCII URIs are, this is called out explicitly. [RFC3986] [RFC3987]

The term root element, when not qualified to explicitly refer to the document's root element, means the furthest ancestor element node of whatever node is being discussed, or the node itself is there is none. 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.

An element is said to have been inserted into a document when its root element changes and is now the document's root element.

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.

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

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.

Various DOM interfaces are defined in this specification using pseudo-IDL. This looks like OMG IDL but isn't. For instance, method overloading is used, and types from the W3C DOM specifications are used without qualification. Language-specific bindings for these abstract interface definitions must be derived in the way consistent with W3C DOM specifications. Some interface-specific binding information for ECMAScript is included in this specification.

The current situation with IDL blocks is pitiful. IDL is totally inadequate to properly represent what objects have to look like in JS; IDL can't say if a member is enumerable, what the indexing behaviour is, what the stringification behaviour is, what behaviour setting a member whose type is a particular interface should be (e.g. setting of document.location or element.className), what constructor an object implementing an interface should claim to have, how overloads work, etc. I think we should make the IDL blocks non-normative, and/or replace them with something else that is better for JS while still being clear on how it applies to other languages. However, we do need to have something that says what types the methods take as arguments, since we have to raise exceptions if they are wrong.

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]

The term text node refers to any Text node, including CDATASection nodes (any Node with node type 3 or 4).

Some of the algorithms in this specification, for historical reasons, require the user agent to pause until some condition has been met. While a user agent is paused, it must ensure that no scripts execute (e.g. no event handlers, no timers, etc). User agents should remain responsive to user input while paused, however.

1.4.1. 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. Generally speaking, authors are discouraged from trying to use XML on the Web, because XML has much stricter syntax rules than the "HTML5" variant described above, and is relatively newer and therefore less mature.

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.

2. The Document Object Model

The Document Object Model (DOM) is a representation — a model — of a document and its content. [DOM3CORE] 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.

This specification defines the language represented in the DOM by features together called DOM5 HTML. DOM5 HTML consists of DOM Core Document nodes and DOM Core Element nodes, along with text nodes and other content.

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.

In addition, documents and elements in the DOM host APIs that extend the DOM Core APIs, providing new features to application developers using DOM5 HTML.

2.1. Documents

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

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 behaviour 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.

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 must implement 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.

interface HTMLDocument {
  // Resource metadata management
  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;

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

  // Dynamic markup insertion
           attribute DOMString innerHTML;
  HTMLDocument open();
  HTMLDocument open(in DOMString type);
  HTMLDocument open(in DOMString type, in DOMString replace);
  Window open(in DOMString url, in DOMString name, in DOMString features);
  Window open(in DOMString url, in DOMString name, in DOMString features, in boolean replace);
  void close();
  void write(in DOMString text);
  void writeln(in DOMString text);

  // Interaction
  readonly attribute Element activeElement;
  readonly attribute boolean hasFocus;

  // Commands
  readonly attribute HTMLCollection commands;

  // Editing
           attribute boolean designMode;
  boolean execCommand(in DOMString commandId);
  boolean execCommand(in DOMString commandId, in boolean doShowUI);
  boolean execCommand(in DOMString commandId, in boolean doShowUI, in DOMString value);
  Selection getSelection();


};

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.

2.1.1. Security

User agents must raise a security exception whenever any of the members of an HTMLDocument object are accessed by scripts whose origin is not the same as the Document's origin.

2.1.2. Resource metadata management

The URL attribute must return the document's address.

The domain attribute must be initialised to the document's domain, if it has one, and null otherwise. On getting, the attribute must return its current value. On setting, if the new value is an allowed value (as defined below), the attribute's value must be changed to the new value. If the new value is not an allowed value, then a security exception must be raised instead.

A new value is an allowed value for the document.domain attribute if it is equal to the attribute's current value, or if the new value, prefixed by a U+002E FULL STOP ("."), exactly matches the end of the current value. If the current value is null, new values other than null will never be allowed.

If the Document object's address is hierarchical and uses a server-based naming authority, then its domain is the <host>/<ihost> part of that address. Otherwise, it has no domain.

The domain attribute is used to enable pages on different hosts of a domain to access each others' DOMs, though this is not yet defined by this specification.

we should handle IP addresses here

The referrer attribute must return either the URI of the page which navigated the browsing context to the current document (if any), or the empty string if there is no such originating page, or if the UA has been configured not to report referrers, 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.

The cookie attribute must, on getting, 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. [RFC2109]

On setting, the cookie attribute must cause the user agent to 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. [RFC2109]

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.

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 timezone, 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 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 filesystem for local files. If the last modification date and time are not known, the attribute must return the string 01/01/1970 00:00:00.

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". The document can also be set to limited quirks mode (also known as "almost standards" mode). By default, the document is set to no quirks mode (also known as "standards mode").

2.2. Elements

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 XHTML elements in XML documents, even when those documents are in another context (e.g. inside an XSLT transform).

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;

  // metadata attributes
           attribute DOMString id;
           attribute DOMString title;
           attribute DOMString lang;
           attribute DOMString dir;
           attribute DOMString className;
  readonly attribute DOMTokenList classList;

  // interaction
           attribute boolean irrelevant;
           attribute long tabIndex;
  void click();
  void focus();
  void blur();
  void scrollIntoView();
  void scrollIntoView(in boolean top);

  // commands
           attribute HTMLMenuElement contextMenu;

  // editing
           attribute boolean draggable;
           attribute DOMString contentEditable;

  // data templates
           attribute DOMString template;
  readonly attribute HTMLDataTemplateElement templateElement;
           attribute DOMString ref;
  readonly attribute Node refNode;
           attribute DOMString registrationMark;
  readonly attribute DocumentFragment originalContent;

  // event handler DOM attributes
           attribute EventListener onabort;
           attribute EventListener onbeforeunload;
           attribute EventListener onblur;
           attribute EventListener onchange;
           attribute EventListener onclick;
           attribute EventListener oncontextmenu;
           attribute EventListener ondblclick;
           attribute EventListener ondrag;
           attribute EventListener ondragend;
           attribute EventListener ondragenter;
           attribute EventListener ondragleave;
           attribute EventListener ondragover;
           attribute EventListener ondragstart;
           attribute EventListener ondrop;
           attribute EventListener onerror;
           attribute EventListener onfocus;
           attribute EventListener onkeydown;
           attribute EventListener onkeypress;
           attribute EventListener onkeyup;
           attribute EventListener onload;
           attribute EventListener onmessage;
           attribute EventListener onmousedown;
           attribute EventListener onmousemove;
           attribute EventListener onmouseout;
           attribute EventListener onmouseover;
           attribute EventListener onmouseup;
           attribute EventListener onmousewheel;
           attribute EventListener onresize;
           attribute EventListener onscroll;
           attribute EventListener onselect;
           attribute EventListener onsubmit;
           attribute EventListener onunload;

};

As with the HTMLDocument interface, 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.

2.2.1. 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.

If a reflecting DOM attribute is a DOMString attribute whose content attribute is defined to contain a URI, then on getting, the DOM attribute must return the value of the content attribute, resolved to an absolute URI, 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 URIs, then on getting, the DOM attribute must split the content attribute on spaces and return the concatenation of each token URI, resolved to an absolute URI, with a single U+0020 SPACE character between each URI; 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 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 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 case-insensitively matches one of the keywords given for that attribute, then the content attribute must be set to that 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 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 the content attribute must be parsed according to the rules for parsing signed integers first. If that fails, 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 a 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 the content attribute must be parsed according to the rules for parsing unsigned integers first. If that fails, 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 a 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 unsigned integers, and if that fails, 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 a 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 the content attribute is defined to contain a time offset, then the content attribute must be parsed according to the rules for parsing time ofsets first. If that fails, or if the attribute is absent, the default value must be returned instead, or the not-a-number value (NaN) if there is no default value. On setting, the given value must be converted to a string using the time offset serialisation rules, and that string must be used as the new content attribute value.

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 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.

2.3. Common DOM interfaces

2.3.1. 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.

2.3.1.1. HTMLCollection

The HTMLCollection interface represents a generic collection of elements.

interface HTMLCollection {
  readonly attribute unsigned long length;
  Element item(in unsigned long index);
  Element namedItem(in DOMString name);
};

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

• It is an a, applet, area, form, img, or object element with a name attribute equal to key, or,
• It is an HTML element of any kind with an id attribute equal to key. (Non-HTML elements, even if they have IDs, are not searched for the purposes of namedItem().)

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

In ECMAScript implementations, objects that implement the HTMLCollection interface must also have a [[Get]] method that, when invoked with a property name that is a number, acts like the item() method would when invoked with that argument, and when invoked with a property name that is a string, acts like the namedItem() method would when invoked with that argument.

2.3.1.2. HTMLFormControlsCollection

The HTMLFormControlsCollection interface represents a collection of form controls.

interface HTMLFormControlsCollection {
  readonly attribute unsigned long length;
  HTMLElement item(in unsigned long index);
  Object namedItem(in DOMString name);
};

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 namedItem(key) 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 key, 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 key, then return null and stop the algorithm.
3. Otherwise, create a NodeList object representing a live view of the HTMLFormControlsCollection 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 key. The nodes in the NodeList object must be sorted in tree order.
4. Return that NodeList object.

In the ECMAScript DOM binding, objects implementing the HTMLFormControlsCollection interface must support being dereferenced using the square bracket notation, such that dereferencing with an integer index is equivalent to invoking the item() method with that index, and such that dereferencing with a string index is equivalent to invoking the namedItem() method with that index.

2.3.1.3. HTMLOptionsCollection

The HTMLOptionsCollection interface represents a list of option elements.

interface HTMLOptionsCollection {
           attribute unsigned long length;
  HTMLOptionElement item(in unsigned long index);
  Object namedItem(in DOMString name);
};

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

On setting, the behaviour 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 namedItem(key) 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 key, 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 key, 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 key. The nodes in the NodeList object must be sorted in tree order.
4. Return that NodeList object.

In the ECMAScript DOM binding, objects implementing the HTMLOptionsCollection interface must support being dereferenced using the square bracket notation, such that dereferencing with an integer index is equivalent to invoking the item() method with that index, and such that dereferencing with a string index is equivalent to invoking the namedItem() method with that index.

We may want to add add() and remove() methods here too because IE implements HTMLSelectElement and HTMLOptionsCollection on the same object, and so people use them almost interchangeably in the wild.

2.3.2. DOMTokenList

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

Which string underlies a particular DOMTokenList object is defined when the object is created. It might be a content attribute (e.g. the string that underlies the classList object is the class attribute), or it might be an anonymous string (e.g. when a DOMTokenList object is passed to an author-implemented callback in the datagrid APIs).

interface DOMTokenList {
  readonly attribute unsigned long length;
  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);
};

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

The item(index) method must split the underlying string on spaces, sort the resulting list of tokens by Unicode codepoint, 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.

In ECMAScript implementations, objects that implement the DOMTokenList interface must also have a [[Get]] method that, when invoked with a property name that is a number, acts like the item() method would when invoked with that argument.

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

1. If the token argument contains any spaces, 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 spaces, 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 last character of the DOMTokenList object's underlying 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 spaces, 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 spaces, 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 last character of the DOMTokenList object's underlying 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.

In the ECMAScript DOM binding, objects implementing the DOMTokenList interface must stringify to the object's underlying string representation.

2.3.3. 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 guarenteed that an implementation that supports "HTML" "5.0" also supports "HTML" "2.0".

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.

The title element of a document is the first title element that is a child of the head element, 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.

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:

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. Stop the algorithm here.

2. If 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.

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.

The images attribute must return an HTMLCollection rooted at the Document node, whose filter matches only img elements.

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 getElementsByName(name) method a string name, and must return a live NodeList containing all the a, applet, button, form, 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.

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 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.

The getElementsByClassName() 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 labelled as being in specific classes. UAs must not assume that all attributes of the name class for elements in any namespace work in this way, however, and must not assume that such attributes, when used as global attributes, label other elements as being in specific classes.

<div id="example">
 <p id="p1" class="aaa bbb"/>
 <p id="p2" class="aaa ccc"/>
 <p id="p3" class="bbb ccc"/>
</div>

The dir attribute on the HTMLDocument interface is defined along with the dir content attribute.

2.5. Dynamic markup insertion

The document.write() family of methods and the innerHTML family of DOM attributes enable script authors to dynamically insert markup into the document.

bz argues that innerHTML should be called something else on XML documents and XML elements. Is the sanity worth the migration pain?

Because these APIs interact with the parser, their behaviour varies depending on whether they are used with HTML documents (and the HTML parser) or XHTML in XML documents (and the XML parser). The following table cross-references the various versions of these APIs.

Regardless of the parsing mode, the document.writeln(...) method must call the document.write() method with the same argument(s), and then call the document.write() method with, as its argument, a string consisting of a single line feed character (U+000A).

2.5.1. Controlling the input stream

The open() method comes in several variants with different numbers of arguments.

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 has 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. onbeforeunload, onunload

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. Remove all child nodes of the document.

7. 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 tokeniser will wait for an explicit call to document.close() before emitting an end-of-file token).

8. Mark the document as being an HTML document (it might already be so-marked).

9. If type does not have the value "text/html", then act as if the tokeniser had emitted a pre element start tag, then set the HTML parser's tokenisation stage's content model flag to PLAINTEXT.

10. 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.)

11. Finally, set the insertion point to point at just before the end of the input stream (which at this point will be empty).

12. Return the Document on which the method was invoked.

We shouldn't hard-code text/plain there. We should do it some other way, e.g. hand off to the section on content-sniffing and handling of incoming data streams, the part that defines how this all works when stuff comes over the network.

When called with three or more arguments, the open() method on the HTMLDocument object must call the open() method on the Window interface of the object returned by the defaultView attribute of the DocumentView interface of the HTMLDocument object, with the same arguments as the original call to the open() method, and return whatever that method returned. If the defaultView attribute of the DocumentView interface of the HTMLDocument object is null, 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 insertion point of the parser's input stream.

2.5.2. Dynamic markup insertion in HTML

In HTML, the document.write(...) method must act as follows:

1. If the insertion point is undefined, the open() method must be called (with no arguments) on the document object. The insertion point will point at just before the end of the (empty) input stream.

2. 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.

3. If there is a script that will execute as soon as the parser resumes, then the method must now return without further processing of the input stream.

4. Otherwise, the tokeniser must process the characters that were inserted, one at a time, processing resulting tokens as they are emitted, and stopping when the tokeniser reaches the insertion point or when the processing of the tokeniser is aborted by the tree construction stage (this can happen if a script start tag token is emitted by the tokeniser).

   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.

5. Finally, the method must return.

In HTML, the innerHTML DOM attribute of all HTMLElement and HTMLDocument nodes returns a serialisation of the node's children using the HTML syntax. On setting, it replaces the node's children with new nodes that result from parsing the given value. The formal definitions follow.

On getting, the innerHTML DOM attribute must return the result of running the HTML fragment serialisation algorithm on the node.

On setting, if the node is a document, the innerHTML DOM attribute must run the following algorithm:

1. 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?

2. Remove the children nodes of the Document whose innerHTML attribute is being set.

3. Create a new HTML parser, in its initial state, and associate it with the Document node.

4. Place into the input stream for the HTML parser just created the string being assigned into the innerHTML attribute.

5. Start the parser and let it run until it has consumed all the characters just inserted into the input stream. (The Document node will have been populated with elements and a load event will have fired on its body element.)

Otherwise, if the node is an element, then setting the innerHTML DOM attribute must cause the following algorithm to run instead:

1. Invoke the HTML fragment parsing algorithm, with the element whose innerHTML attribute is being set as the context and the string being assigned into the innerHTML attribute as the input. Let new children be the result of this algorithm.

2. Remove the children of the element whose innerHTML attribute is being set.

3. Let target document be the ownerDocument of the Element node whose innerHTML attribute is being set.

4. Set the ownerDocument of all the nodes in new children to the target document.

5. Append all the new children nodes to the node whose innerHTML attribute is being set, preserving their order.

script elements inserted using innerHTML do not execute when they are inserted.

2.5.3. Dynamic markup insertion in XML

In an XML context, the document.write() method must raise an INVALID_ACCESS_ERR exception.

On the other hand, however, the innerHTML attribute is indeed usable in an XML context.

In an XML context, the innerHTML DOM attribute on HTMLElements and HTMLDocuments, on getting, must return a string in the form of an internal general parsed entity that is XML namespace-well-formed, the string being an isomorphic serialisation of all of that node's child nodes, in document order. User agents may adjust prefixes and namespace declarations in the serialisation (and indeed might be forced to do so in some cases to obtain namespace-well-formed XML). [XML] [XMLNS]

If any of the following cases are found in the DOM being serialised, the user agent must raise an INVALID_STATE_ERR exception:

• A DocumentType node that has an external subset public identifier or an external subset system identifier that contains both a U+0022 QUOTATION MARK ('"') and a U+0027 APOSTROPHE ("'").
• A node with a prefix or local name containing a U+003A COLON (":").
• A Text node whose data contains characters that are not matched by the XML Char production. [XML]
• A CDATASection node whose data contains the string "]]>".
• A Comment node whose data contains two adjacent U+002D HYPHEN-MINUS (-) characters or ends with such a character.
• A ProcessingInstruction node whose target name is the string "xml" (case insensitively).
• A ProcessingInstruction node whose target name contains a U+003A COLON (":").
• A ProcessingInstruction node whose data contains the string "?>".

These are the only ways to make a DOM unserialisable. 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.

On setting, in an XML context, the innerHTML DOM attribute on HTMLElements and HTMLDocuments must run the following algorithm:

1. The user agent must create a new XML parser.

2. If the innerHTML attribute is being set on an element, the user agent must 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.

3. The user agent must feed the parser just created the string being assigned into the innerHTML attribute.

4. If the innerHTML attribute is being set on an element, the user agent must feed the parser the string corresponding to the end tag of that element.

5. If the parser found a well-formedness error, the attribute's setter must raise a SYNTAX_ERR exception and abort these steps.

6. The user agent must remove the children nodes of the node whose innerHTML attribute is being set.

7. If the attribute is being set on a Document node, let new children be the children of the document, preserving their order. Otherwise, the attribute is being set on an Element node; let new children be the children of the the document's root element, preserving their order.

8. 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.

9. Set the ownerDocument of all the nodes in new children to the target document.

10. Append all the new children nodes to the node whose innerHTML attribute is being set, preserving their order.

script elements inserted using innerHTML do not execute when they are inserted.

2.6. 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 summarised 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, Node.nodeName, and Node.localName

These attributes return tag names in all uppercase and attribute names in all lowercase, 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.setAttributeNode()

When an Attr node is set on an HTML element, it must have its name lowercased before the element is affected.

This doesn't apply to Document.setAttributeNodeNS().

Element.setAttribute()

When an attribute is set on an HTML element, the name argument must be lowercased before the element is affected.

This doesn't apply to Document.setAttributeNS().

Document.getElementsByTagName() and Element.getElementsByTagName()

These methods (but not their namespaced counterparts) must compare the given argument case-insensitively when looking at HTML elements, and case-sensitively 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.

Document.renameNode()

If the new namespace is the HTML namespace, then the new qualified name must be lowercased before the rename takes place.

3. Semantics and structure of HTML elements

3.1. Introduction

This section is non-normative.

An introduction to marking up a document.

3.2. 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.

3.2.1. 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+000B LINE TABULATION, U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).

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 Zs characters means that the user agent must collect a sequence of characters that are in the Unicode character class Zs. In both cases, the collected characters are not used. [UNICODE]

3.2.2. 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 the attribute's canonical name, exactly, with no leading or trailing whitespace, and in lowercase.

3.2.3. Numbers

3.2.3.1. Unsigned integers

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

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 indeed 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 not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

7. 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).

8. Return value.

3.2.3.2. Signed integers

A string is a valid integer if it consists of one of 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.

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.

3.2.3.3. Real numbers

A string is a valid floating point number if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally with a single U+002E FULL STOP (".") character somewhere (either before these numbers, in between two numbers, or after the numbers), all optionally prefixed with a U+002D HYPHEN-MINUS ("-") character.

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 a value. 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 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) or U+002E FULL STOP ("."), then return an error.

9. If the next character is U+002E FULL STOP ("."), but either that is the last character or the character after that one is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

10. 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 past the end of input, then if sign is "positive", return value, otherwise return 0-value.
    5. Otherwise return to the top of step 10 in the overall algorithm (that's the step within which these substeps find themselves).

11. Otherwise, if the next character is not a U+002E FULL STOP ("."), then if sign is "positive", return value, otherwise return 0-value.

12. The next character is a U+002E FULL STOP ("."). Advance position to the character after that.

13. Let divisor be 1.

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

    1. Multiply divisor by ten.
    2. Add the value of the current character (0..9) divided by divisor, to value.
    3. Advance position to the next character.
    4. If position is past the end of input, then if sign is "positive", return value, otherwise return 0-value.
    5. Otherwise return to the top of step 14 in the overall algorithm (that's the step within which these substeps find themselves).

15. Otherwise, if sign is "positive", return value, otherwise return 0-value.

3.2.3.4. 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.

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 any characters in the string that are in the Unicode character class Zs (this might match zero characters). [UNICODE]
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 nothing and abort these steps.
11. Set number2 to the number returned by the sub-algorithm in step 9.
12. 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.
13. 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.
14. 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 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 guarenteed to be a valid floating point number).
6. Return number.

3.2.3.5. Percentages and dimensions

valid positive non-zero integers rules for parsing dimension values (only used by height/width on img, embed, object — lengths in css pixels or percentages)

3.2.3.6. 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 U+002C COMMA character or a U+0020 SPACE 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+002C COMMA character or a U+0020 SPACE character, return to step 4.

7. Let negated be false.

8. Let value be 0.

9. Let multiple be 1.

10. Let started be false.

11. Let finished be false.

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 finished is true, skip to the next step in the overall set of steps.
    2. If started is true or if bogus is true, let negated be false.
    3. Otherwise, if started is false and if bogus is false, let negated be true.
    4. 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. Let n be the value of the digit, interpreted in base ten, multiplied by multiple.
    3. Add n to value.
    4. If value is greater than zero, multiply multiple by ten.
    5. Let started be true.

    A U+002C COMMA character

    A U+0020 SPACE character

    Follow these substeps:

    1. If started is false, return the numbers list and abort.
    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 U+002E FULL STOP character

    Follow these substeps:

    1. Let finished be true.

    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 started is true, then append value to the numbers list, return that list, and abort.

18. Return the numbers list and abort.

3.2.4. 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]

3.2.4.1. Specific moments in time

A string is a valid datetime if it has four digits (representing the year), a literal hyphen, two digits (representing the month), a literal hyphen, two digits (representing the day), optionally some spaces, either a literal T or a space, optionally some more spaces, two digits (for the hour), a colon, two digits (the minutes), optionally the seconds (which, if included, must consist of another colon, two digits (the integer part of the seconds), and optionally a decimal point followed by one or more digits (for the fractional part of the seconds)), optionally some spaces, and finally either a literal Z (indicating the time zone is UTC), or, a plus sign or a minus sign followed by two digits, a colon, and two digits (for the sign, the hours and minutes of the timezone offset respectively); with the month-day combination being a valid date in the given year according to the Gregorian calendar, the hour values (h) being in the range 0 ≤ h ≤ 23, the minute values (m) in the range 0 ≤ m ≤ 59, and the second value (s) being in the range 0 ≤ h < 60. [GREGORIAN]

The digits must be characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), the hyphens must be a U+002D HYPHEN-MINUS characters, the T must be a U+0054 LATIN CAPITAL LETTER T, the colons must be U+003A COLON characters, the decimal point must be a U+002E FULL STOP, the Z must be a U+005A LATIN CAPITAL LETTER Z, the plus sign must be a U+002B PLUS SIGN, and the minus U+002D (same as the hyphen).

Conformance checkers can use the algorithm below to determine if a datetime is a valid datetime or not.

To parse a string as a datetime value, a user agent must apply the following algorithm to the string. This will either return a time in UTC, with associated timezone information for round tripping or display purposes, or nothing, indicating the value is not a valid datetime. If at any point the algorithm says that it "fails", this means that it 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 exactly four characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the year.

4. 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.

5. 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.

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

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

8. 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.

9. 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.

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

11. Collect a sequence of characters that are either U+0054 LATIN CAPITAL LETTER T characters or space characters. If the collected sequence is zero characters long, or if it contains more than one U+0054 LATIN CAPITAL LETTER T character, then fail.

12. 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.

13. If hour is not a number in the range 0 ≤ hour ≤ 23, then fail.

14. 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.

15. 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.

16. If minute is not a number in the range 0 ≤ minute ≤ 59, then fail.

17. Let second be a string with the value "0".

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

19. If the character at position is a U+003A COLON, then:

    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.

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

21. If second is not a number in the range 0 ≤ hour < 60, then fail. (The values 60 and 61 are not allowed: leap seconds cannot be represented by datetime values.)

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

23. Skip whitespace.

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

    1. Let timezone_hours be 0.

    2. Let timezone_minutes be 0.

    3. Advance position to the next character in input.

25. 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 timezone_hours.

    4. If timezone_hours is not a number in the range 0 ≤ timezone_hours ≤ 23, then fail.
    5. If sign is "negative", then negate timezone_hours.

    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 timezone_minutes.

    8. If timezone_minutes is not a number in the range 0 ≤ timezone_minutes ≤ 59, then fail.
    9. If sign is "negative", then negate timezone_minutes.

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

27. Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezone_hours hours and timezone_minutes minutes. That moment in time is a moment in the UTC timezone.

28. Let timezone be timezone_hours hours and timezone_minutes minutes from UTC.

29. Return time and timezone.

3.2.4.2. Vaguer moments in time

This section defines date or time strings. There are two kinds, date or time strings in content, and date or time strings in attributes. The only difference is in the handling of whitespace characters.

To parse a date or time string, user agents must use the following algorithm. A date or time string is a valid date or time string if the following algorithm, when run on the string, doesn't say the string is invalid.

The algorithm may return nothing (in which case the string will be invalid), or it may return a date, a time, a date and a time, or a date and a time and and a timezone. Even if the algorithm returns one or more values, the string can still be invalid.

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 results be the collection of results that are to be returned (one or more of a date, a time, and a timezone), initially empty. If the algorithm aborts at any point, then whatever is currently in results must be returned as the result of the algorithm.

4. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

6. Let the sequence of characters collected in the last step be s.

7. If position is past the end of input, the string is invalid; abort these steps.

8. If the character at position is not a U+003A COLON character, then:

   1. If the character at position is not a U+002D HYPHEN-MINUS ("-") character either, then the string is invalid, abort these steps.

   2. If the sequence s is not exactly four digits long, then the string is invalid. (This does not stop the algorithm, however.)

   3. Interpret the sequence of characters collected in step 5 as a base ten integer, and let that number be year.

   4. Advance position past the U+002D HYPHEN-MINUS ("-") character.

   5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

   6. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

   7. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be month.

   8. If month is not a number in the range 1 ≤ month ≤ 12, then the string is invalid, abort these steps.

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

   10. If position is past the end of input, or if the character at position is not a U+002D HYPHEN-MINUS ("-") character, then the string is invalid, abort these steps. Otherwise, advance position to the next character.

   11. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

   12. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

   13. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be day.

   14. If day is not a number in the range 1 ≤ day ≤ maxday, then the string is invalid, abort these steps.

   15. Add the date represented by year, month, and day to the results.

   16. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

   17. If the character at position is a U+0054 LATIN CAPITAL LETTER T, then move position forwards one character.

   18. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

   19. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

   20. Let s be the sequence of characters collected in the last step.

9. If s is not exactly two digits long, then the string is invalid.

10. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be hour.

11. If hour is not a number in the range 0 ≤ hour ≤ 23, then the string is invalid, abort these steps.

12. If position is past the end of input, or if the character at position is not a U+003A COLON character, then the string is invalid, abort these steps. Otherwise, advance position to the next character.

13. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

14. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

15. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be minute.

16. If minute is not a number in the range 0 ≤ minute ≤ 59, then the string is invalid, abort these steps.

17. Let second be 0. It may be changed to another value in the next step.

18. If position is not past the end of input and the character at position is a U+003A COLON character, then:

    1. Collect a sequence of characters that are either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) or are U+002E FULL STOP. If the collected sequence is empty, or contains more than one U+002E FULL STOP character, then the string is invalid; abort these steps.

    2. If the first character in the sequence collected in the last step is not in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then the string is invalid.

    3. Interpret the sequence of characters collected two steps ago as a base ten number (possibly with a fractional part), and let that number be second.

    4. If second is not a number in the range 0 ≤ minute < 60, then the string is invalid, abort these steps.

19. Add the time represented by hour, minute, and second to the results.

20. If results has both a date and a time, then:

    1. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

    2. If position is past the end of input, then skip to the next step in the overall set of steps.

    3. Otherwise, if the character at position is a U+005A LATIN CAPITAL LETTER Z, then:

       1. Add the timezone corresponding to UTC (zero offset) to the results.

       2. Advance position to the next character in input.

       3. Skip to the next step in the overall set of steps.

    4. 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 the string is invalid.

       4. Interpret the sequence collected in the last step as a base ten number, and let that number be timezone_hours.

       5. If timezone_hours is not a number in the range 0 ≤ timezone_hours ≤ 23, then the string is invalid; abort these steps.
       6. If sign is "negative", then negate timezone_hours.

       7. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then the string is invalid; abort these steps. Otherwise, move position forwards one character.

       8. 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 the string is invalid.

       9. Interpret the sequence collected in the last step as a base ten number, and let that number be timezone_minutes.

       10. If timezone_minutes is not a number in the range 0 ≤ timezone_minutes ≤ 59, then the string is invalid; abort these steps.

       11. Add the timezone corresponding to an offset of timezone_hours hours and timezone_minutes minutes to the results.

       12. Skip to the next step in the overall set of steps.

    5. Otherwise, the string is invalid; abort these steps.

21. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

22. If position is not past the end of input, then the string is invalid.

23. Abort these steps (the string is parsed).

3.2.5. Time offsets

valid time offset, rules for parsing time offsets, time offset serialisation rules; in the format "5d4h3m2s1ms" or "3m 9.2s" or "00:00:00.00" or similar.

3.2.6. 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.

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.

3.2.7. 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 one of the given keywords that are not said to be non-conforming, with no leading or trailing whitespace. The keyword may use any mix of uppercase and lowercase letters.

When the attribute is specified, if its value case-insensitively matches 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 simply 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.

3.2.8. References

A valid hashed ID 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 id attribute of an element in the document with type type.

The rules for parsing a hashed ID 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 or name attribute whose value case-insensitively matches s.

3.3. Documents and document fragments

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 only use elements, attributes, and attribute values for their appropriate semantic purposes.

<!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>

<!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/"><cite>Ernest</cite></a>,
   in an essay from 1992
  </p>
 </body>
</html>

<body>
 <h1>ABC Company</h1>
 <h2>Leading the way in widget design since 1432</h2>
 ...

<body>
 <header>
  <h1>ABC Company</h1>
  <h2>Leading the way in widget design since 1432</h2>
 </header>
 ...

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. Structure

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. Authors must only put elements inside an element if that element allows them to be there according to its content model.

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 only use elements in the HTML namespace in the contexts where they are allowed, as defined for each element. For XML compound documents, these contexts could be inside elements from other namespaces, if those elements are defined as providing the relevant contexts.

3.3.3. Kinds of content

Each element in HTML falls into zero or more categories that group elements with similar characteristics together. The following categories are used in this specification:

• Metadata content
• Prose content
• Sectioning content
• Heading content
• Phrasing content
• Embedded content
• Form control content
• Interactive content

Some elements have unique requirements and do not fit into any particular category.

3.3.3.1. Metadata content

Metadata content is content that sets up the presentation or behaviour 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.

3.3.3.2. Prose content

Most elements that are used in the body of documents and applications are categorised as prose content.

As a general rule, elements whose content model allows any prose 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.

3.3.3.3. Sectioning content

Sectioning content is content that defines the scope of headers, footers, and contact information.

Each sectioning content element potentially has a heading. See the section on headings and sections for further details.

3.3.3.4. 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).

3.3.3.5. 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.

All phrasing content is also prose content. Any content model that expects prose content also expects phrasing content.

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 categorised as phrasing content can only contain elements that are themselves categorised as phrasing content, not any prose content.

Text nodes that are not inter-element whitespace are phrasing content.

3.3.3.6. Embedded content

Embedded content is content that imports another resource into the document, or content from another vocabulary that is inserted into the document.

All embedded content is also phrasing content (and prose content). Any content model that expects phrasing content (or prose content) also expects embedded content.

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.

3.3.3.7. Interactive content

Parts of this section should eventually be moved to DOM3 Events.

Interactive content is content that is specifically intended for user interaction.

Certain elements in HTML can be activated, for instance a elements, button elements, or input elements when their type attribute is set to radio. Activation of those elements can happen in various (UA-defined) ways, for instance via the mouse or keyboard.

When activation is performed via some method other than clicking the pointing device, the default action of the event that triggers the activation must, instead of being activating the element directly, be to fire a click event on the same element.

The default action of this click event, or of the real click event if the element was activated by clicking a pointing device, must be to fire a further DOMActivate event at the same element, whose own default action is to go through all the elements the DOMActivate event bubbled through (starting at the target node and going towards the Document node), looking for an element with an activation behavior; the first element, in reverse tree order, to have one, must have its activation behavior executed.

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.

For certain form controls, this process is complicated further by changes that must happen around the click event. [WF2]

Most interactive elements have content models that disallow nesting interactive elements.

3.3.4. Transparent content models

Some elements are described as transparent; they have "transparent" as their content model. Some elements are described as semi-transparent; this means that part of their content model is "transparent" but that is not the only part of the content model that must be satisfied.

When a content model includes a part that is "transparent", those parts must only contain content that would still be conformant if all transparent and semi-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 or semi-transparent element has no parent, then the part of its content model that is "transparent" must instead be treated as accepting any prose content.

3.3.5. 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 prose content are defined relative to what the document looks like without the ins and del elements complicating matters. Let view be a view of the DOM that replaces all ins and del elements in the document with their contents. Then, in view, for each run of phrasing content 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 run, a paragraph exists in the original DOM from immediately before first to immediately after last. (Paragraphs can thus span across ins and del elements.)

A paragraph is also formed 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.

<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>

<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>

3.4. Global attributes

The following attributes are common to and may be specified on all HTML elements (even those not defined in this specification):

Global attributes:

class

contenteditable

contextmenu

dir

draggable

id

irrelevant

lang

ref

registrationmark

tabindex

template

title

In addition, the following event handler content attributes may be specified on any HTML element:

Event handler content attributes:

onabort

onbeforeunload

onblur

onchange

onclick

oncontextmenu

ondblclick

ondrag

ondragend

ondragenter

ondragleave

ondragover

ondragstart

ondrop

onerror

onfocus

onkeydown

onkeypress

onkeyup

onload

onmessage

onmousedown

onmousemove

onmouseout

onmouseover

onmouseup

onmousewheel

onresize

onscroll

onselect

onsubmit

onunload

3.4.1. The id attribute

The id attribute represents its element's unique identifier. The value must be unique in the subtree within which the element finds itself 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 subtree the element finds itself (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.

3.4.2. 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.

Some elements, such as link and dfn, define additional semantics for the title attribute beyond the semantics described above.

The title DOM attribute must reflect the title content attribute.

3.4.3. The lang (HTML only) and xml:lang (XML only) 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 is defined in XML. [XML]

If these attributes are omitted from an element, then it implies that the language of this element is the same as the language of the parent element. Setting the attribute to the empty string indicates that the primary language is unknown.

The lang attribute may only be used on elements of HTML documents. Authors must not use the lang attribute in XML documents.

The xml:lang attribute may only be used on elements of XML documents. Authors must not use the xml:lang attribute in HTML documents.

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, 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).

User agents may use the element's language to determine proper processing or rendering (e.g. in the selection of appropriate fonts or pronounciations, or for dictionary selection).

The lang DOM attribute must reflect the lang content attribute.

3.4.4. 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.

If the attribute has the state ltr, the element's directionality is left-to-right. If the attribute has the state rtl, the element's directionality is right-to-left. Otherwise, the element's directionality is the same as its parent.

The processing of this attribute depends on the presentation layer. For example, CSS 2.1 defines a mapping from this attribute to the CSS 'direction' and 'unicode-bidi' properties, and defines rendering in terms of those properties.

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.

3.4.5. 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.

3.4.6. The irrelevant attribute

All elements may have the irrelevant content attribute set. The irrelevant 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 irrelevant attribute specified.

  <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').irrelevant = true;
      document.getElementById('game').irrelevant = false;
    }
   </script>
  </section>
  <section id="game" irrelevant>
   ...
  </section>

The irrelevant attribute must not be used to hide content that could legitimately be shown in another presentation. For example, it is incorrect to use irrelevant 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 irrelevant 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 irrelevant DOM attribute must reflect the content attribute of the same name.

3.5. Interaction

3.5.1. Activation

The click() method must fire a click event at the element, whose default action is the firing of a further DOMActivate event at the same element, whose own default action is to go through all the elements the DOMActivate event bubbled through (starting at the target node and going towards the Document node), looking for an element with an activation behavior; the first element, in reverse tree order, to have one, must have its activation behavior executed.

3.5.2. Focus

When an element is focused, key events received by the document must be targeted at that element. There is always an element focused; in the absence of other elements being focused, the document's root element is it.

Which element within a document currently has focus is independent of whether or not the document itself has the system focus.

Some focusable elements might take part in sequential focus navigation.

3.5.2.1. Focus management

The focus() and blur() methods must focus and unfocus the element respectively, if the element is focusable.

Some elements, most notably area, can correspond to more than one distinct focusable area. When such an element is focused using the focus() method, the first such region in tree order is the one that must be focused.

Well that clearly needs more.

The activeElement attribute must return the element in the document that has focus. If no element specifically has focus, this must return the body element.

The hasFocus attribute must return true if the document, one of its nested browsing contexts, or any element in the document or its browsing contexts currently has the system focus.

3.5.2.2. Sequential focus navigation

This section on the tabindex attribute needs to be checked for backwards-compatibility.

The tabindex attribute specifies the relative order of elements 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.

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. If parsing the value returns an error, the attribute is ignored for the purposes of focus management (as if it wasn't specified).

A positive integer or zero specifies the index of the element in the current scope's tab order. Elements with the same index are sorted in tree order for the purposes of tabbing.

A negative integer specifies that the element should be removed from the tab order. If the element does normally take focus, it may still be focused using other means (e.g. it could be focused by a click).

If the attribute is absent (or invalid), then the user agent must treat the element as if it had the value 0 or the value -1, based on platform conventions.

For example, a user agent might default textarea elements to 0, and button elements to -1, making text fields part of the tabbing cycle but buttons not.

When an element that does not normally take focus (i.e. whose default value would be -1) has the tabindex attribute specified with a positive value, then it should be added to the tab order and should be made focusable. When focused, the element matches the CSS :focus pseudo-class and key events are dispatched on that element in response to keyboard input.

The tabIndex DOM attribute reflects the value of the tabIndex content attribute. If the attribute is not present (or has an invalid value) then the DOM attribute must return the UA's default value for that element, which will be either 0 (for elements in the tab order) or -1 (for elements not in the tab order).

3.5.3. Scrolling elements into view

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 must instead simply align the top of the element with the top of the viewport.

Non-visual user agents may ignore the argument, or may treat it in some media-specific manner most useful to the user.

3.6. The root element

3.6.1. 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.

Element-specific attributes:

manifest

DOM interface:

No difference from 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 URI (or IRI).

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). Furthermore, as it is processed before any base elements are seen, its value is not subject to being made relative to any base URI.

Though it has absolutely no effect and no meaning, the html element, in HTML documents, 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 the null 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 the null namespace specified.

3.7. Document metadata

3.7.1. 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.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The head element collects the document's metadata.

3.7.2. 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.

Element-specific attributes:

None.

DOM interface:

No difference from 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 header, since the first header 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.

  <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...

  <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.

3.7.3. 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.

Element-specific attributes:

href

target

DOM interface:

interface HTMLBaseElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
};

The base element allows authors to specify the document's base URI for the purposes of resolving relative URIs, and the name of the default browsing context for the purposes of following hyperlinks.

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 URI (or IRI).

A base element, if it has an href attribute, must come before any other elements in the tree that have attributes with URIs (except the html element and its manifest attribute).

User agents must use the value of the href attribute of the first base element that is both a child of the head element and has an href attribute, if there is such an element, as the document entity's base URI for the purposes of section 5.1.1 of RFC 3986 ("Establishing a Base URI": "Base URI Embedded in Content"). This base URI from RFC 3986 is referred to by the algorithm given in XML Base, which is a normative part of this specification. [RFC3986]

If the base URI given by this attribute is a relative URI, it must be resolved relative to the higher-level base URIs (i.e. the base URI from the encapsulating entity or the URI used to retrieve the entity) to obtain an absolute base URI. All xml:base attributes must be ignored when resolving relative URIs in this href attribute.

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. User agents use this name when following hyperlinks.

A base element, if it has a target attribute, must come before any elements in the tree that represent hyperlinks.

The href and target DOM attributes must reflect the content attributes of the same name.

3.7.4. The link element

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.

Element-specific attributes:

href

rel

media

hreflang

type

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;
};

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 is given by the href attribute, which must be present and must contain a URI (or IRI). If the href attribute is absent, then the element does not define a link.

The type of link indicated (the relationship) is 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 value used is 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). User agents should process the links on a per-link basis, not a per-element basis.

The exact behaviour 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. (However, user agents may opt to only fetch such resources when they are needed, instead of pro-actively downloading all the external resources that are not applied.)

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:

• The relationship between this document and the resource (given by the rel attribute)
• The title of the resource (given by the title attribute).
• The URI of the resource (given by the href attribute).
• The language of the resource (given by the hreflang attribute).
• The optimum media for the resource (given by the media attribute).

User agents may also include other information, such as the type of the resource (as given by the type attribute).

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 only apply the external resource to views while their state match the listed media.

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, user agents may use the type given in this attribute to decide whether or not to consider using the resource at all. If the UA does not support the given MIME type for the given link relationship, then the UA may opt not to download and apply the resource.

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.

If the attribute is omitted, then the UA must fetch the resource to determine its type and thus determine if it supports (and can apply) that external resource.

<link rel="stylesheet" href="A" type="text/css">
<link rel="stylesheet" href="B" type="text/plain">
<link rel="stylesheet" href="C">

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.

Some versions of HTTP defined a Link: header, to be processed like a series of link elements. When processing links, those must be taken into consideration as well. 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. Relative URIs in these headers must be resolved according to the rules given in HTTP, not relative to base URIs set by the document (e.g. using a base element or xml:base attributes). [RFC2616] [RFC2068]

The DOM attributes href, rel, media, hreflang, and type 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.

3.7.5. The meta element

Categories

Metadata content.

Contexts in which this element may be used:

If the charset attribute is present: as the first element in a head element.

If the http-equiv attribute is present: in a head element.

If the http-equiv attribute is present: 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.

Element-specific attributes:

name

http-equiv

content

charset (HTML only)

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 serialised 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 may only be specified in HTML documents, it must not be used in XML documents. If the charset attribute is specified, the element must be the first element in the head element of the file.

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.

3.7.5.1. Standard metadata names

This specification defines a few names for the name attribute of the meta element.

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. WYSIWYG editors have additional constraints on the value used with this metadata name.

dns

The value must be an ordered set of unique space-separated tokens, each word of which is a host name. The list allows authors to provide a list of host names that the user is expected to subsequently need. User agents may, according to user preferences and prevailing network conditions, pre-emptively resolve the given DNS names (extracting the names from the value using the rules for splitting a string on spaces), thus precaching the DNS information for those hosts and potentially reducing the time between page loads for subsequent user interactions. Higher priority should be given to host names given earlier in the list.

3.7.5.2. 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 URIs must not be proposed or accepted. Links must be represented using the link element, not the meta element.

3.7.5.3. 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 the rows with keywords give the states to which those keywords map.

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:

Refresh state

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. Let url be equal to the substring of input from the character at position to the end of the string.

19. Strip any trailing space characters from the end of url.

20. Strip any U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), and U+000D CARRIAGE RETURN (CR) characters from url.

21. Resolve the url value to an absolute URI using the base URI of the meta element.

22. Set a timer so that in time seconds, if the user has not canceled the redirect, the user agent navigates to url, with replacement enabled.

For meta elements in the Refresh state, the content attribute must have a value consisting either of:

• just a valid non-negative integer, or
• a valid non-negative integer, followed by a U+003B SEMICOLON (;), followed by one or more space characters, followed by either a U+0055 LATIN CAPITAL LETTER U or a U+0075 LATIN SMALL LETTER U, a U+0052 LATIN CAPITAL LETTER R or a U+0072 LATIN SMALL LETTER R, a U+004C LATIN CAPITAL LETTER L or a U+006C LATIN SMALL LETTER L, a U+003D EQUALS SIGN (=), and then a valid URI (or IRI).

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 URI.

Default style state

1. ...

3.7.5.4. Specifying the document's character encoding

The meta element may also be used to provide UAs with character encoding information for HTML files, by setting the charset attribute to the name of a character encoding. This is called a character encoding declaration.

The following restrictions apply to character encoding declarations:

• The character encoding name given must be the name of the character encoding used to serialise the file.
• The value must be a valid character encoding name, and must be the preferred name for that encoding. [IANACHARSET]
• The attribute value must be serialised without the use of character entity references of any kind.

If the 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 a superset of US-ASCII (specifically, ANSI_X3.4-1968) for bytes in the range 0x09 - 0x0D, 0x20, 0x21, 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A, and 0x61 - 0x7A , 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.

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.

3.7.6. The style element

Categories

Metadata content.

If the scoped attribute is present: prose 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 prose content is expected, but before any sibling elements other than style elements and before any text nodes other than inter-element whitespace.

Content model:

Depends on the value of the type attribute.

Element-specific 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.

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 only apply the styles to views while their state match the listed media. [DOM3VIEWS]

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 the attribute is present, then the user agent must only apply the specified style information 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.

If the scoped attribute is not specified, the style element must be the child of a head element or of a noscript element that is a child of a head element.

If the scoped attribute is specified, then the style element must be the child of a prose content element, before any text nodes other than inter-element whitespace, and before any elements other than other style elements.

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 children nodes of the style element to the style system.

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.

3.7.7. 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 downloaded, 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 URI given by the element's href content attribute. 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.

3.8. 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.

3.8.1. The body element

Categories

Sectioning content.

Contexts in which this element may be used:

As the second element in an html element.

Content model:

Prose content.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

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.

3.8.2. The section element

Categories

Prose content.

Sectioning content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Prose content.

Element-specific attributes:

None.

DOM interface:

No difference from 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 header, 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.

3.8.3. The nav element

Categories

Prose content.

Sectioning content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Prose content.

Element-specific attributes:

None.

DOM interface:

No difference from 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.

3.8.4. The article element

Categories

Prose content.

Sectioning content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Prose content.

Element-specific attributes:

None.

DOM interface:

No difference from 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.

3.8.5. The blockquote element

Categories

Prose content.

Sectioning content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Prose content.

Element-specific 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 URI, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a URI (or IRI). User agents should allow users to follow such citation links.

If a blockquote element is preceded or followed by a paragraph that contains a single cite element and is itself not preceded or followed by another blockquote element and does not itself have a q element descendant, then, the citation given by that cite element gives the source of the quotation contained in the blockquote element.

The cite DOM attribute reflects the element's cite content attribte.

The best way to represent a conversation is not with the cite and blockquote elements, but with the dialog element.

3.8.6. The aside element

Categories

Prose content.

Sectioning content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Prose content.

Element-specific attributes:

None.

DOM interface:

No difference from 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.

3.8.7. The h1, h2, h3, h4, h5, and h6 elements

Categories

Prose content.

Heading content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Phrasing content.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

These elements define headers 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.

3.8.8. The header element

Categories

Prose content.

Heading content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Prose content, including at least one descendant that is heading content, but no sectioning content descendants, no header element descendants, and no footer element descendants.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The header element represents the header of a section. Headers may contain more than just the section's heading — for example it would be reasonable for the header to include version history information.

For the purposes of document summaries, outlines, and the like, header elements are equivalent to the highest ranked h1-h6 element descendant of the header element (the first such element if there are multiple elements with that rank).

Other heading elements in the header element indicate subheadings or subtitles.

<header>
 <h1>The reality dysfunction</h1>
 <h2>Space is not the only void</h2>
</header>

<header>
 <p>Welcome to...</p>
 <h1>Voidwars!</h1>
</header>

<header>
 <h1>Scalable Vector Graphics (SVG) 1.2</h1>
 <h2>W3C Working Draft 27 October 2004</h2>
 <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 section on headings and sections defines how header elements are assigned to individual sections.

The rank of a header element is the same as for an h1 element (the highest rank).

3.8.9. The footer element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Prose content, but with no heading content descendants, no sectioning content descendants, and no footer element descendants.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The footer element represents the 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 given in a footer should be marked up using the address element.

3.8.10. The address element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Prose content, but with no heading content descendants, no sectioning content descendants, no footer element descendants, and no address element descendants.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The address element represents the contact information for the section it applies to.

<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.

<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 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 element and its ancestor sectioning elements. The contact information is the collection of all the information given by those elements.

Contact information for one sectioning element, e.g. an aside element, does not apply to its ancestor elements, e.g. the page's body.

3.8.11. Headings and sections

The h1-h6 elements and the header element are headings.

The first element of heading content in an element of sectioning content gives the header for that section. Subsequent headers of equal or higher rank start new (implied) sections, headers of lower rank start subsections that are part of the previous one.

Sectioning elements other than blockquote are always considered subsections of their nearest ancestor element of sectioning content, regardless of what implied sections other headings may have created. However, blockquote elements are associated with implied sections. Effectively, blockquote elements act like sections on the inside, and act opaquely on the outside.

<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>

Sections may contain headers 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 explictly wrap sections in elements of sectioning content, instead of relying on the implicit sections generated by having multiple heading in one element of sectioning content.

<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>

<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>

3.8.11.1. Creating an outline

This section will be rewritten at some point. The algorithm likely won't change, but its description will be dramatically simplified.

Documents can be viewed as a tree of sections, which defines how each element in the tree is semantically related to the others, in terms of the overall section structure. This tree is related to the document tree, but there is not a one-to-one relationship between elements in the DOM and the document's sections.

The tree of sections should be used when generating document outlines, for example when generating tables of contents.

To derive the tree of sections from the document tree, a hypothetical tree is used, consisting of a view of the document tree containing only the elements of heading content and the elements of sectioning content other than blockquote. Descendants of h1-h6, header, and blockquote elements must be removed from this view.

The hypothetical tree must be rooted at the root element or at an element of sectioning content. In particular, while the sections inside blockquotes do not contribute to the document's tree of sections, blockquotes can have outlines of their own.

UAs must take this hypothetical tree (which will become the outline) and mutate it by walking it depth first in tree order and, for each element of heading content that is not the first element of its parent sectioning content element, inserting a new element of sectioning content, as follows:

If the element is a header element, or if it is an h1-h6 node of rank equal to or higher than the first element in the parent element of sectioning content (assuming that is also an h1-h6 node), or if the first element of the parent element of sectioning content is an element of sectioning content:

Insert the new element of sectioning content as the immediately following sibling of the parent element of sectioning content, and move all the elements from the current element of heading content up to the end of the parent element of sectioning content into the new element of sectioning content.

Otherwise:

Move the current heading element, and all subsequent siblings up to but excluding the next element of sectioning content, header element, or h1-h6 of equal or higher rank, whichever comes first, into the new element of sectioning content, then insert the new element of sectioning content where the current header was.

The outline is then the resulting hypothetical tree. The ranks of the headers become irrelevant at this point: each element of sectioning content in the hypothetical tree contains either no or one heading element child. If there is one, then it gives the section's heading, of there isn't, the section has no heading.

Sections are nested as in the hypothetical tree. If a sectioning element is a child of another, that means it is a subsection of that other section.

When creating an interactive table of contents, entries should jump the user to the relevant section element, if it was a real element in the original document, or to the heading, if the section element was one of those created during 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 header in the body is to be found.

function (n) {
  // This implementation only knows about HTML elements.
  // An implementation that supports other languages might be
  // different.

  // Reject anything that isn't an element.
  if (n.nodeType != Node.ELEMENT_NODE)
    return NodeFilter.FILTER_REJECT;

  // Skip any descendants of headings.
  if ((n.parentNode && n.parentNode.namespaceURI == 'http://www.w3.org/1999/xhtml') &&
      (n.parentNode.localName == 'h1' || n.parentNode.localName == 'h2' ||
       n.parentNode.localName == 'h3' || n.parentNode.localName == 'h4' ||
       n.parentNode.localName == 'h5' || n.parentNode.localName == 'h6' ||
       n.parentNode.localName == 'header'))
    return NodeFilter.FILTER_REJECT;

  // Skip any blockquotes.
  if ((n.namespaceURI == 'http://www.w3.org/1999/xhtml') &&
      (n.localName == 'blockquote'))
    return NodeFilter.FILTER_REJECT;

  // Accept HTML elements in the list given in the prose above.
  if ((n.namespaceURI == 'http://www.w3.org/1999/xhtml') &&
      (n.localName == 'body' || /*n.localName == 'blockquote' ||*/
       n.localName == 'section' || n.localName == 'nav' ||
       n.localName == 'article' || n.localName == 'aside' ||
       n.localName == 'h1' || n.localName == 'h2' ||
       n.localName == 'h3' || n.localName == 'h4' ||
       n.localName == 'h5' || n.localName == 'h6' ||
       n.localName == 'header'))
    return NodeFilter.FILTER_ACCEPT;

  // Skip the rest.
  return NodeFilter.FILTER_SKIP;
}

3.8.11.2. Determining which heading and section applies to a particular node

This section will be rewritten at some point. The algorithm likely won't change, but its description will be dramatically simplified.

Given a particular node, user agents must use the following algorithm, in the given order, to determine which heading and section the node is most closely associated with. The processing of this algorithm must stop as soon as the associated section and heading are established (even if they are established to be nothing).

1. If the node has an ancestor that is a header element, then the associated heading is the most distant such ancestor. The associated section is that header's associated section (i.e. repeat this algorithm for that header).
2. If the node has an ancestor that is an h1-h6 element, then the associated heading is the most distant such ancestor. The associated section is that heading's section (i.e. repeat this algorithm for that heading element).
3. If the node is an h1-h6 element or a header element, then the associated heading is the element itself. The UA must then generate the hypothetical section tree described in the previous section, rooted at the nearest section ancestor (or the root element if there is no such ancestor). If the parent of the heading in that hypothetical tree is an element in the real document tree, then that element is the associated section. Otherwise, there is no associated section element.
4. If the node is an element of sectioning content, then the associated section is itself. The UA must then generate the hypothetical section tree described in the previous section, rooted at the section itself. If the section element, in that hypothetical tree, has a child element that is an h1-h6 element or a header element, then that element is the associated heading. Otherwise, there is no associated heading element.
5. If the node is a footer or address element, then the associated section is the nearest ancestor element of sectioning content, if there is one. The node's associated heading is the same as that element of sectioning content's associated heading (i.e. repeat this algorithm for that element of sectioning content). If there is no ancestor element of sectioning content, the element has no associated section nor an associated heading.
6. Otherwise, the node is just a normal node, and the document has to be examined more closely to determine its section and heading. Create a view rooted at the nearest ancestor element of sectioning content (or the root element if there is none) that has just h1-h6 elements, header elements, the node itself, and elements of sectioning content other than blockquote elements. (Descendants of any of the nodes in this view can be ignored, as can any node later in the tree than the node in question, as the algorithm below merely walks backwards up this view.)
7. Let n be an iterator for this view, initialised at the node in question.
8. Let c be the current best candidate heading, initially null, and initially not used. It is used when top-level heading candidates are to be searched for (see below).
9. Repeat these steps (which effectively goes backwards through the node's previous siblings) until an answer is found:
   1. If n points to a node with no previous sibling, and c is null, then return the node's parent node as the answer. If the node has no parent node, return null as the answer.
   2. Otherwise, if n points to a node with no previous sibling, return c as the answer.
   3. Adjust n so that it points to the previous sibling of the current position.
   4. If n is pointing at an h1 or header element, then return that element as the answer.
   5. If n is pointing at an h2-h6 element, and heading candidates are not being searched for, then return that element as the answer.
   6. Otherwise, if n is pointing at an h2-h6 element, and either c is still null, or c is a heading of lower rank than this one, then set c to be this element, and continue going backwards through the previous siblings.
   7. If n is pointing at an element of sectioning content, then from this point on top-level heading candidates are being searched for. (Specifically, we are looking for the nearest top-level header for the current section.) Continue going backwards through the previous siblings.
10. If the answer from the previous step (the loop) is null, which can only happen if the node has no preceeding headings and is not contained in an element of sectioning content, then there is no associated heading and no associated section.
11. Otherwise, if the answer from the earlier loop step is an element of sectioning content, then the associated section is that element and the associated heading is that element of sectioning content's associated heading (i.e. repeat this algorithm for that section).
12. Otherwise, if the answer from that same earlier step is an h1-h6 element or a header element, then the associated heading is that element and the associated section is that heading element's associated section (i.e. repeat this algorithm for that heading).

Not all nodes have an associated header or section. For example, if a section is implied, as when multiple headers are found in one element of sectioning content, then a node in that section has an anonymous associated section (its section is not represented by a real element), and the algorithm above does not associate that node with any particular element of sectioning content.

<body>
 <h1>X</h1>
 <h2>X</h2>
 <blockquote>
  <h3>X</h3>
 </blockquote>
 <p id="a">X</p>
 <h4>Text Node A</h4>
 <section>
  <h5>X</h5>
 </section>
 <p>Text Node B</p>
</body>

3.8.11.3. Distinguishing site-wide headers from page headers

Given the hypothetical section tree, but ignoring any sections created for nav and aside elements, and any of their descendants, if the 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 header of the body element should be assumed to be a site-wide header, and the header of the article element should be assumed to be the page's header.

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 hypothetical section tree, ignoring any sections created for nav and aside elements and any of their descendants, the root of the tree is 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 header 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 hypothetical section tree, 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.

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.

3.9. Prose

3.9.1. The p element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Phrasing content.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The p element represents a paragraph.

<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.

<section>
 <!-- ... -->
 <p>Last modified: 2001-04-23</p>
 <p>Author: fred@example.com</p>
</section>

<section>
 <!-- ... -->
 <footer>Last modified: 2001-04-23</footer>
 <address>Author: fred@example.com</address>
</section>

<section>
 <!-- ... -->
 <footer>
  <p>Last modified: 2001-04-23</p>
  <address>Author: fred@example.com</address>
 </footer>
</section>

3.9.2. The hr element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Empty.

Element-specific attributes:

None.

DOM interface:

No difference from 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.

3.9.3. The br element

Categories

Phrasing content.

Contexts in which this element may be used:

Where phrasing content is expected.

Content model:

Empty.

Element-specific attributes:

None.

DOM interface:

No difference from 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 only be used for line breaks that are actually part of the content, as in poems or addresses.

<p>P. Sherman<br>
42 Wallaby Way<br>
Sydney</p>

br elements must not be used for separating thematic groups in a paragraph.

<p><a ...>34 comments.</a><br>
<a ...>Add a comment.<a></p>

<p>Name: <input name="name"><br>
Address: <input name="address"></p>

<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.

3.9.4. The dialog element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Zero or more pairs of dt and dd elements.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The dialog element represents a conversation.

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.

<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 someone else. See the cite, q, and blockquote elements for other ways to cite or quote.

3.10. Preformatted text

3.10.1. The pre element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Phrasing content.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The pre element represents a block of preformatted text, in which structure is represented by typographic conventions rather than by elements.

Some examples of cases where the pre element could be used:

• Including an e-mail, with paragraphs indicated by blank lines, lists indicated by lines prefixed with a bullet, and so on.
• Including fragments of computer code, with structure indicated according to the conventions of that language.
• Displaying ASCII art.

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.

<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>

<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>

<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>

3.11. Lists

3.11.1. The ol element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Zero or more li elements.

Element-specific attributes:

start

DOM interface:

interface HTMLOListElement : HTMLElement {
           attribute long start;
};

The ol element represents an ordered list of items (which are represented by li elements).

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.

The items of the list are the li element child nodes of the ol element, in tree order.

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.

The start DOM attribute must reflect the value of the start content attribute.

3.11.2. The ul element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Zero or more li elements.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The ul element represents an unordered list of items (which are represented by li elements).

The items of the list are the li element child nodes of the ul element.

3.11.3. The li element

Categories

None.

Contexts in which this element may be used:

Inside ol elements.

Inside ul elements.

Inside menu elements.

Content model:

When the element is a child of a menu element: phrasing content.

Otherwise: prose content.

Element-specific attributes:

If the element is a child of an ol element: value

If the element is not the child of an ol element: None.

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 first 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.

3.11.4. The dl element

Categories

Prose content.

Contexts in which this element may be used:

Where prose content is expected.

Content model:

Zero or more groups each consisting of one or more dt elements followed by one or mode dd elements.

Element-specific attributes:

None.

DOM interface:

No difference from HTMLElement.

The dl element introduces an unordered 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.

<dl>
 <dt> Authors
 <dd> John
 <dd> Luke
 <dt> Editor
 <dd> Frank
</dl>

<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>

<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>

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, and the document is non-conforming.

If a dl element contains only dt elements, then it consists of one group with names but no values, and the document is non-conforming.

If a dl element contains only dd elements, then it consists of one group with values but no names, and the document is non-conforming.

The dl element is inappropriate for marking up dialogue, since dialogue is ordered (each speaker/line pair comes after the next). For an example of how to mark up dialogue, see the dialog element.

3.11.5. 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.

Element-specific attributes:

None.

DOM interface:

No difference from 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.

3.11.6. 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:

Prose content.

Element-specific attributes:

None.

DOM interface:

No difference from 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).

3.12. Phrase elements

3.12.1. The a element

Categories

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.

Element-specific attributes:

href

target

ping

rel

media

hreflang

type

DOM interface:

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;
};

The Command interface must also be implemented by this element.

If the a element has an href attribute, then it represents a hyperlink.

If the a element has no href attribute, then the element is 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.

<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 DOMActivate 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 to the location of the click, and let y be the distance in CSS pixels from the top edge of the image 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.

One way that a user agent can enable users to follow hyperlinks is by allowing a elements to be clicked, or focussed and activated by the keyboard. This will cause the aforementioned activation behavior to be invoked.

The DOM attributes href, ping, target, rel, media, hreflang, and type, must each reflect the respective content attributes of the same name.

The DOM attribute relList must reflect the rel content attribute.

3.12.2. The q element

Categories

Phrasing content.

Contexts in which this element may be used:

Where phrasing content is expected.

Content model:

Phrasing content.

Element-specific attributes:

cite

DOM interface:

The q element uses the HTMLQuoteElement interface.

The q element represents a part of a paragraph quoted from another source.

Content inside a q element must be quoted from another source, whose URI, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a URI (or IRI). User agents should allow users to follow such citation links.

If a q element is contained (directly or indirectly) in a paragraph that contains a single cite element and has no other q element descendants, then, the citation given by that cite element gives the source of the quotation contained in the q element.