HTML 5

Abstract

This specification evolves HTML and its related APIs to ease the authoring of Web-based applications. Additions include the context menus, a direct-mode graphics canvas, inline popup windows, and server-sent events. Heavy emphasis is placed on keeping the language backwards compatible with existing legacy user agents and on keeping user agents backwards compatible with existing legacy documents.

Status of this document

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

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

Implementors should be aware that this specification is not stable. Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the call for implementations should join the WHATTF 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 Background
  • 1.2 Scope
  • 1.3 Relationships to other specifications
    • 1.3.1 Relationship to HTML 4.01 and DOM2 HTML
    • 1.3.2 Relationship to XHTML 1.x
    • 1.3.3 Relationship to XHTML2
    • 1.3.4 Relationship to Web Forms 2.0 and XForms
    • 1.3.5 Relationship to XUL, Flash, Silverlight, and other proprietary UI languages
  • 1.4 HTML vs XHTML
  • 1.5 Structure of this specification
    • 1.5.1 How to read this specification
• 2. Common infrastructure
  • 2.1 Conformance requirements
    • 2.1.1 Dependencies
    • 2.1.2 Features defined in other specifications
    • 2.1.3 Common conformance requirements for APIs exposed to JavaScript
  • 2.2 Terminology
  • 2.3 URLs
    • 2.3.1 Terminology
    • 2.3.2 Parsing URLs
    • 2.3.3 Resolving URLs
    • 2.3.4 Dynamic changes to base URLs
    • 2.3.5 Interfaces for URL manipulation
  • 2.4 Common microsyntaxes
    • 2.4.1 Common parser idioms
    • 2.4.2 Boolean attributes
    • 2.4.3 Numbers
      • 2.4.3.1. Unsigned integers
      • 2.4.3.2. Signed integers
      • 2.4.3.3. Real numbers
      • 2.4.3.4. Ratios
      • 2.4.3.5. Percentages and dimensions
      • 2.4.3.6. Lists of integers
    • 2.4.4 Dates and times
      • 2.4.4.1. Specific moments in time
      • 2.4.4.2. Vaguer moments in time
    • 2.4.5 Time offsets
    • 2.4.6 Tokens
    • 2.4.7 Keywords and enumerated attributes
    • 2.4.8 References
  • 2.5 Common DOM interfaces
    • 2.5.1 Reflecting content attributes in DOM attributes
    • 2.5.2 Collections
      • 2.5.2.1. HTMLCollection
      • 2.5.2.2. HTMLFormControlsCollection
      • 2.5.2.3. HTMLOptionsCollection
    • 2.5.3 DOMTokenList
    • 2.5.4 DOMStringMap
    • 2.5.5 DOM feature strings
  • 2.6 Fetching resources
  • 2.7 Determining the type of a resource
    • 2.7.1 Content-Type metadata
    • 2.7.2 Content-Type sniffing: Web pages
    • 2.7.3 Content-Type sniffing: text or binary
    • 2.7.4 Content-Type sniffing: unknown type
    • 2.7.5 Content-Type sniffing: image
    • 2.7.6 Content-Type sniffing: feed or HTML
• 3. Semantics and structure of HTML documents
  • 3.1 Introduction
  • 3.2 Documents
    • 3.2.1 Documents in the DOM
    • 3.2.2 Security
    • 3.2.3 Resource metadata management
    • 3.2.4 DOM tree accessors
  • 3.3 Elements
    • 3.3.1 Semantics
    • 3.3.2 Elements in the DOM
    • 3.3.3 Global attributes
      • 3.3.3.1. The id attribute
      • 3.3.3.2. The title attribute
      • 3.3.3.3. The lang (HTML only) and xml:lang (XML only) attributes
      • 3.3.3.4. The xml:base attribute (XML only)
      • 3.3.3.5. The dir attribute
      • 3.3.3.6. The class attribute
      • 3.3.3.7. The style attribute
      • 3.3.3.8. Embedding custom non-visible data
  • 3.4 Content models
    • 3.4.1 Kinds of content
      • 3.4.1.1. Metadata content
      • 3.4.1.2. Flow content
      • 3.4.1.3. Sectioning content
      • 3.4.1.4. Heading content
      • 3.4.1.5. Phrasing content
      • 3.4.1.6. Embedded content
      • 3.4.1.7. Interactive content
    • 3.4.2 Transparent content models
  • 3.5 Paragraphs
  • 3.6 APIs in HTML documents
  • 3.7 Dynamic markup insertion
    • 3.7.1 Controlling the input stream
    • 3.7.2 Dynamic markup insertion in HTML
    • 3.7.3 Dynamic markup insertion in XML
• 4. The elements of HTML
  • 4.1 The root element
    • 4.1.1 The html element
  • 4.2 Document metadata
    • 4.2.1 The head element
    • 4.2.2 The title element
    • 4.2.3 The base element
    • 4.2.4 The link element
    • 4.2.5 The meta element
      • 4.2.5.1. Standard metadata names
      • 4.2.5.2. Other metadata names
      • 4.2.5.3. Pragma directives
      • 4.2.5.4. Specifying the document's character encoding
    • 4.2.6 The style element
    • 4.2.7 Styling
  • 4.3 Sections
    • 4.3.1 The body element
    • 4.3.2 The section element
    • 4.3.3 The nav element
    • 4.3.4 The article element
    • 4.3.5 The aside element
    • 4.3.6 The h1, h2, h3, h4, h5, and h6 elements
    • 4.3.7 The header element
    • 4.3.8 The footer element
    • 4.3.9 The address element
    • 4.3.10 Headings and sections
      • 4.3.10.1. Creating an outline
      • 4.3.10.2. Distinguishing site-wide headings from page headings
  • 4.4 Grouping content
    • 4.4.1 The p element
    • 4.4.2 The hr element
    • 4.4.3 The br element
    • 4.4.4 The pre element
    • 4.4.5 The dialog element
    • 4.4.6 The blockquote element
    • 4.4.7 The ol element
    • 4.4.8 The ul element
    • 4.4.9 The li element
    • 4.4.10 The dl element
    • 4.4.11 The dt element
    • 4.4.12 The dd element
  • 4.5 Text-level semantics
    • 4.5.1 The a element
    • 4.5.2 The q element
    • 4.5.3 The cite element
    • 4.5.4 The em element
    • 4.5.5 The strong element
    • 4.5.6 The small element
    • 4.5.7 The mark element
    • 4.5.8 The dfn element
    • 4.5.9 The abbr element
    • 4.5.10 The time element
    • 4.5.11 The progress element
    • 4.5.12 The meter element
    • 4.5.13 The code element
    • 4.5.14 The var element
    • 4.5.15 The samp element
    • 4.5.16 The kbd element
    • 4.5.17 The sub and sup elements
    • 4.5.18 The span element
    • 4.5.19 The i element
    • 4.5.20 The b element
    • 4.5.21 The bdo element
    • 4.5.22 The ruby element
    • 4.5.23 The rt element
    • 4.5.24 The rp element
    • 4.5.25 Usage summary
    • 4.5.26 Footnotes
  • 4.6 Edits
    • 4.6.1 The ins element
    • 4.6.2 The del element
    • 4.6.3 Attributes common to ins and del elements
    • 4.6.4 Edits and paragraphs
    • 4.6.5 Edits and lists
  • 4.7 Embedded content
    • 4.7.1 The figure element
    • 4.7.2 The img element
    • 4.7.3 The iframe element
    • 4.7.4 The embed element
    • 4.7.5 The object element
    • 4.7.6 The param element
    • 4.7.7 The video element
      • 4.7.7.1. Video and audio codecs for video elements
    • 4.7.8 The audio element
      • 4.7.8.1. Audio codecs for audio elements
    • 4.7.9 The source element
    • 4.7.10 Media elements
      • 4.7.10.1. Error codes
      • 4.7.10.2. Location of the media resource
      • 4.7.10.3. Network states
      • 4.7.10.4. Loading the media resource
      • 4.7.10.5. Offsets into the media resource
      • 4.7.10.6. The ready states
      • 4.7.10.7. Playing the media resource
      • 4.7.10.8. Seeking
      • 4.7.10.9. Cue ranges
      • 4.7.10.10. User interface
      • 4.7.10.11. Time ranges
      • 4.7.10.12. Byte ranges
      • 4.7.10.13. Event summary
      • 4.7.10.14. Security and privacy considerations
    • 4.7.11 The canvas element
      • 4.7.11.1. The 2D context
        • 4.7.11.1.1. The canvas state
        • 4.7.11.1.2. Transformations
        • 4.7.11.1.3. Compositing
        • 4.7.11.1.4. Colors and styles
        • 4.7.11.1.5. Line styles
        • 4.7.11.1.6. Shadows
        • 4.7.11.1.7. Simple shapes (rectangles)
        • 4.7.11.1.8. Complex shapes (paths)
        • 4.7.11.1.9. Text
        • 4.7.11.1.10. Images
        • 4.7.11.1.11. Pixel manipulation
        • 4.7.11.1.12. Drawing model
      • 4.7.11.2. Color spaces and color correction
      • 4.7.11.3. Security with canvas elements
    • 4.7.12 The map element
    • 4.7.13 The area element
    • 4.7.14 Image maps
    • 4.7.15 MathML
    • 4.7.16 SVG
    • 4.7.17 Dimension attributes
  • 4.8 Tabular data
    • 4.8.1 Introduction
    • 4.8.2 The table element
    • 4.8.3 The caption element
    • 4.8.4 The colgroup element
    • 4.8.5 The col element
    • 4.8.6 The tbody element
    • 4.8.7 The thead element
    • 4.8.8 The tfoot element
    • 4.8.9 The tr element
    • 4.8.10 The td element
    • 4.8.11 The th element
    • 4.8.12 Attributes common to td and th elements
    • 4.8.13 Processing model
      • 4.8.13.1. Forming a table
      • 4.8.13.2. Forming relationships between data cells and header cells
  • 4.9 Forms
    • 4.9.1 The form element
    • 4.9.2 The fieldset element
    • 4.9.3 The input element
    • 4.9.4 The button element
    • 4.9.5 The label element
    • 4.9.6 The select element
    • 4.9.7 The datalist element
    • 4.9.8 The optgroup element
    • 4.9.9 The option element
    • 4.9.10 The textarea element
    • 4.9.11 The output element
    • 4.9.12 Processing model
      • 4.9.12.1. Form submission
  • 4.10 Scripting
    • 4.10.1 The script element
      • 4.10.1.1. Scripting languages
    • 4.10.2 The noscript element
    • 4.10.3 The event-source element
  • 4.11 Interactive elements
    • 4.11.1 The details element
    • 4.11.2 The datagrid element
      • 4.11.2.1. The datagrid data model
      • 4.11.2.2. How rows are identified
      • 4.11.2.3. The data provider interface
      • 4.11.2.4. The default data provider
        • 4.11.2.4.1. Common default data provider method definitions for cells
      • 4.11.2.5. Populating the datagrid element
      • 4.11.2.6. Updating the datagrid
      • 4.11.2.7. Requirements for interactive user agents
      • 4.11.2.8. The selection
      • 4.11.2.9. Columns and captions
    • 4.11.3 The command element
    • 4.11.4 The menu element
      • 4.11.4.1. Introduction
      • 4.11.4.2. Building menus and tool bars
      • 4.11.4.3. Context menus
      • 4.11.4.4. Toolbars
    • 4.11.5 Commands
      • 4.11.5.1. Using the a element to define a command
      • 4.11.5.2. Using the button element to define a command
      • 4.11.5.3. Using the input element to define a command
      • 4.11.5.4. Using the option element to define a command
      • 4.11.5.5. Using the command element to define a command
  • 4.12 Data Templates
    • 4.12.1 Introduction
    • 4.12.2 The datatemplate element
    • 4.12.3 The rule element
    • 4.12.4 The nest element
    • 4.12.5 Global attributes for data templates
    • 4.12.6 Processing model
      • 4.12.6.1. The originalContent DOM attribute
      • 4.12.6.2. The template attribute
      • 4.12.6.3. The ref attribute
      • 4.12.6.4. The NodeDataTemplate interface
      • 4.12.6.5. Mutations
      • 4.12.6.6. Updating the generated content
  • 4.13 Miscellaneous elements
    • 4.13.1 The legend element
    • 4.13.2 The div element
• 5. Web browsers
  • 5.1 Browsing contexts
    • 5.1.1 Nested browsing contexts
    • 5.1.2 Auxiliary browsing contexts
    • 5.1.3 Secondary browsing contexts
    • 5.1.4 Security
    • 5.1.5 Threads
    • 5.1.6 Browsing context names
  • 5.2 The default view
    • 5.2.1 Security
    • 5.2.2 Constructors
    • 5.2.3 APIs for creating and navigating browsing contexts by name
    • 5.2.4 Accessing other browsing contexts
  • 5.3 Origin
    • 5.3.1 Relaxing the same-origin restriction
  • 5.4 Scripting
    • 5.4.1 Script execution contexts
    • 5.4.2 Security exceptions
    • 5.4.3 The javascript: protocol
    • 5.4.4 Events
      • 5.4.4.1. Event handler attributes
      • 5.4.4.2. Event firing
      • 5.4.4.3. Events and the Window object
      • 5.4.4.4. Runtime script errors
  • 5.5 User prompts
    • 5.5.1 Simple dialogs
    • 5.5.2 Printing
    • 5.5.3 Dialogs implemented using separate documents
    • 5.5.4 Notifications
  • 5.6 Browser state
    • 5.6.1 Custom protocol and content handlers
      • 5.6.1.1. Security and privacy
      • 5.6.1.2. Sample user interface
  • 5.7 Offline Web applications
    • 5.7.1 Introduction
    • 5.7.2 Application caches
    • 5.7.3 The cache manifest syntax
      • 5.7.3.1. Writing cache manifests
      • 5.7.3.2. Parsing cache manifests
    • 5.7.4 Updating an application cache
    • 5.7.5 Processing model
      • 5.7.5.1. Changes to the networking model
    • 5.7.6 Application cache API
    • 5.7.7 Browser state
  • 5.8 Session history and navigation
    • 5.8.1 The session history of browsing contexts
    • 5.8.2 The History interface
    • 5.8.3 Activating state object entries
    • 5.8.4 The Location interface
      • 5.8.4.1. Security
    • 5.8.5 Implementation notes for session history
  • 5.9 Browsing the Web
    • 5.9.1 Navigating across documents
    • 5.9.2 Page load processing model for HTML files
    • 5.9.3 Page load processing model for XML files
    • 5.9.4 Page load processing model for text files
    • 5.9.5 Page load processing model for images
    • 5.9.6 Page load processing model for content that uses plugins
    • 5.9.7 Page load processing model for inline content that doesn't have a DOM
    • 5.9.8 Navigating to a fragment identifier
    • 5.9.9 History traversal
  • 5.10 Structured client-side storage
    • 5.10.1 Storing name/value pairs
      • 5.10.1.1. Introduction
      • 5.10.1.2. The Storage interface
      • 5.10.1.3. The sessionStorage attribute
      • 5.10.1.4. The localStorage attribute
      • 5.10.1.5. The storage event
        • 5.10.1.5.1. Event definition
      • 5.10.1.6. Threads
    • 5.10.2 Database storage
      • 5.10.2.1. Introduction
      • 5.10.2.2. Databases
      • 5.10.2.3. Executing SQL statements
      • 5.10.2.4. Database query results
      • 5.10.2.5. Errors
      • 5.10.2.6. Processing model
    • 5.10.3 Disk space
    • 5.10.4 Privacy
      • 5.10.4.1. User tracking
      • 5.10.4.2. Cookie resurrection
    • 5.10.5 Security
      • 5.10.5.1. DNS spoofing attacks
      • 5.10.5.2. Cross-directory attacks
      • 5.10.5.3. Implementation risks
      • 5.10.5.4. SQL and user agents
      • 5.10.5.5. SQL injection
  • 5.11 Links
    • 5.11.1 Hyperlink elements
    • 5.11.2 Following hyperlinks
      • 5.11.2.1. Hyperlink auditing
    • 5.11.3 Link types
      • 5.11.3.1. Link type "alternate"
      • 5.11.3.2. Link type "archives"
      • 5.11.3.3. Link type "author"
      • 5.11.3.4. Link type "bookmark"
      • 5.11.3.5. Link type "external"
      • 5.11.3.6. Link type "feed"
      • 5.11.3.7. Link type "help"
      • 5.11.3.8. Link type "icon"
      • 5.11.3.9. Link type "license"
      • 5.11.3.10. Link type "nofollow"
      • 5.11.3.11. Link type "noreferrer"
      • 5.11.3.12. Link type "pingback"
      • 5.11.3.13. Link type "prefetch"
      • 5.11.3.14. Link type "search"
      • 5.11.3.15. Link type "stylesheet"
      • 5.11.3.16. Link type "sidebar"
      • 5.11.3.17. Link type "tag"
      • 5.11.3.18. Hierarchical link types
        • 5.11.3.18.1. Link type "index"
        • 5.11.3.18.2. Link type "up"
      • 5.11.3.19. Sequential link types
        • 5.11.3.19.1. Link type "first"
        • 5.11.3.19.2. Link type "last"
        • 5.11.3.19.3. Link type "next"
        • 5.11.3.19.4. Link type "prev"
      • 5.11.3.20. Other link types
• 6. User Interaction
  • 6.1 Introduction
  • 6.2 The irrelevant attribute
  • 6.3 Activation
  • 6.4 Scrolling elements into view
  • 6.5 Focus
    • 6.5.1 Focus management
    • 6.5.2 Sequential focus navigation
  • 6.6 The text selection APIs
    • 6.6.1 APIs for the browsing context selection
    • 6.6.2 APIs for the text field selections
  • 6.7 The contenteditable attribute
    • 6.7.1 User editing actions
    • 6.7.2 Making entire documents editable
  • 6.8 Drag and drop
    • 6.8.1 Introduction
    • 6.8.2 The DragEvent and DataTransfer interfaces
    • 6.8.3 Events fired during a drag-and-drop action
    • 6.8.4 Drag-and-drop processing model
      • 6.8.4.1. When the drag-and-drop operation starts or ends in another document
      • 6.8.4.2. When the drag-and-drop operation starts or ends in another application
    • 6.8.5 The draggable attribute
    • 6.8.6 Copy and paste
      • 6.8.6.1. Copy to clipboard
      • 6.8.6.2. Cut to clipboard
      • 6.8.6.3. Paste from clipboard
      • 6.8.6.4. Paste from selection
    • 6.8.7 Security risks in the drag-and-drop model
  • 6.9 Undo history
    • 6.9.1 The UndoManager interface
    • 6.9.2 Undo: moving back in the undo transaction history
    • 6.9.3 Redo: moving forward in the undo transaction history
    • 6.9.4 The UndoManagerEvent interface and the undo and redo events
    • 6.9.5 Implementation notes
  • 6.10 Command APIs
• 7. Communication
  • 7.1 Event definitions
  • 7.2 Server-sent DOM events
    • 7.2.1 The RemoteEventTarget interface
    • 7.2.2 Connecting to an event stream
    • 7.2.3 Parsing an event stream
    • 7.2.4 Interpreting an event stream
    • 7.2.5 Notes
  • 7.3 Web sockets
    • 7.3.1 Introduction
    • 7.3.2 The WebSocket interface
    • 7.3.3 WebSocket Events
    • 7.3.4 The Web Socket protocol
      • 7.3.4.1. Client-side requirements
        • 7.3.4.1.1. Handshake
        • 7.3.4.1.2. Data framing
      • 7.3.4.2. Server-side requirements
        • 7.3.4.2.1. Minimal handshake
        • 7.3.4.2.2. Handshake details
        • 7.3.4.2.3. Data framing
      • 7.3.4.3. Closing the connection
  • 7.4 Cross-document messaging
    • 7.4.1 Processing model
• 8. Repetition templates
• 9. The HTML syntax
  • 9.1 Writing HTML documents
    • 9.1.1 The DOCTYPE
    • 9.1.2 Elements
      • 9.1.2.1. Start tags
      • 9.1.2.2. End tags
      • 9.1.2.3. Attributes
      • 9.1.2.4. Optional tags
      • 9.1.2.5. Restrictions on content models
      • 9.1.2.6. Restrictions on the contents of CDATA and RCDATA elements
    • 9.1.3 Text
      • 9.1.3.1. Newlines
    • 9.1.4 Character references
    • 9.1.5 CDATA blocks
    • 9.1.6 Comments
  • 9.2 Parsing HTML documents
    • 9.2.1 Overview of the parsing model
    • 9.2.2 The input stream
      • 9.2.2.1. Determining the character encoding
      • 9.2.2.2. Character encoding requirements
      • 9.2.2.3. Preprocessing the input stream
      • 9.2.2.4. Changing the encoding while parsing
    • 9.2.3 Parse state
      • 9.2.3.1. The insertion mode
      • 9.2.3.2. The stack of open elements
      • 9.2.3.3. The list of active formatting elements
      • 9.2.3.4. The element pointers
      • 9.2.3.5. The scripting state
    • 9.2.4 Tokenisation
      • 9.2.4.1. Tokenising character references
    • 9.2.5 Tree construction
      • 9.2.5.1. Creating and inserting elements
      • 9.2.5.2. Closing elements that have implied end tags
      • 9.2.5.3. Foster parenting
      • 9.2.5.4. The "initial" insertion mode
      • 9.2.5.5. The "before html" insertion mode
      • 9.2.5.6. The "before head" insertion mode
      • 9.2.5.7. The "in head" insertion mode
      • 9.2.5.8. The "in head noscript" insertion mode
      • 9.2.5.9. The "after head" insertion mode
      • 9.2.5.10. The "in body" insertion mode
      • 9.2.5.11. The "in table" insertion mode
      • 9.2.5.12. The "in caption" insertion mode
      • 9.2.5.13. The "in column group" insertion mode
      • 9.2.5.14. The "in table body" insertion mode
      • 9.2.5.15. The "in row" insertion mode
      • 9.2.5.16. The "in cell" insertion mode
      • 9.2.5.17. The "in select" insertion mode
      • 9.2.5.18. The "in select in table" insertion mode
      • 9.2.5.19. The "in foreign content" insertion mode
      • 9.2.5.20. The "after body" insertion mode
      • 9.2.5.21. The "in frameset" insertion mode
      • 9.2.5.22. The "after frameset" insertion mode
      • 9.2.5.23. The "after after body" insertion mode
      • 9.2.5.24. The "after after frameset" insertion mode
    • 9.2.6 The end
  • 9.3 Namespaces
  • 9.4 Serializing HTML fragments
  • 9.5 Parsing HTML fragments
  • 9.6 Named character references
• 10. Rendering and user-agent behavior
  • 10.1 Rendering and the DOM
  • 10.2 Rendering and menus/toolbars
    • 10.2.1 The 'icon' property
  • 10.3 Obsolete elements, attributes, and APIs
    • 10.3.1 The body element
    • 10.3.2 The applet element
• 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 Localization
  • 11.2 Declarative 2D vector graphics and animation
  • 11.3 Declarative 3D scenes
  • 11.4 Timers
• Index
• References
• Acknowledgements

1. Introduction

1.1 Background

This section is non-normative.

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

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

1.2 Scope

This section is non-normative.

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

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

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

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

For sophisticated cross-platform applications, there already exist several proprietary solutions (such as Mozilla's XUL, Adobe's Flash, or Microsoft's Silverlight). 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.

1.3 Relationships to other specifications

1.3.1 Relationship to HTML 4.01 and DOM2 HTML

This section is non-normative.

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

1.3.2 Relationship to XHTML 1.x

This section is non-normative.

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

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

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

1.3.3 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.

1.3.4 Relationship to Web Forms 2.0 and XForms

This section is non-normative.

This specification will eventually supplant Web Forms 2.0. The current Web Forms 2.0 draft can be considered part of this specification for the time being; its features will eventually be merged into this specification. [WF2]

As it stands today, this specification is unrelated and orthognoal to XForms. When the forms features defined in HTML4 and Web Forms 2.0 are merged into this specification, then the relationship to XForms described in the Web Forms 2.0 draft will apply to this specification. [XForms]

1.3.5 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, vendor-neutral language, HTML provides for a solution to the same problems without the risk of vendor lock-in.

1.4 HTML vs XHTML

This section is non-normative.

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

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

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

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

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

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

1.5 Structure of this specification

This section is non-normative.

This specification is divided into the following major sections:

Common Infrastructure

The conformance classes, algorithms, definitions, and the common underpinnings of the rest of the specification.

The DOM

Documents are built from elements. These elements form a tree using the DOM. This section defines the features of this DOM, as well as introducing the features common to all elements, and the concepts used in defining elements.

Elements

Each element has a predefined meaning, which is explained in this section. User agent requirements for how to handle each element are also given, along with rules for authors on how to use the element.

Web Browsers

HTML documents do not exist in a vacuum — this section defines many of the features that affect environments that deal with multiple pages, links between pages, and running scripts.

User Interaction

HTML documents can provide a number of mechanisms for users to interact with and modify content, which are described in this section.

The Communication APIs

Applications written in HTML often require mechanisms to communicate with remote servers, as well as communicating with other applications from different domains running on the same client.

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 serialized form and sent to other people, and so this section defines the syntax of HTML, along with rules for how to parse HTML.

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

1.5.1 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.

2. Common infrastructure

2.1 Conformance requirements

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

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

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

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

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

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

Web browsers and other interactive user agents

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

A conforming XHTML processor would, upon finding an XHTML script element in an XML document, execute the script contained in that element. However, if the element is found within 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 labeled 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 entirely) are exempt from supporting the events and DOM interfaces mentioned in this specification. For the parts of this specification that are defined in terms of an events model or in terms of the DOM, such user agents must still act as if events and the DOM were supported.

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

Conformance checkers

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

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

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

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

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

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

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

Data mining tools

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

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

Authoring tools and markup generators

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

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

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

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

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

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

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

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

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

Some conformance requirements are phrased as requirements on elements, attributes, methods or objects. Such requirements fall into two categories: those describing content model restrictions, and those describing implementation behavior. 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 entity references for characters in XHTML documents is unsafe (except for <, >, &, " and ').

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

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

2.1.1 Dependencies

This specification relies on several other underlying specifications.

XML

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

DOM

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

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

ECMAScript

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

Media Queries

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

This specification does not require support of any particular network transport protocols, style sheet language, scripting language, or any of the DOM and WebAPI specifications beyond those described above. However, the language described by this specification is biased towards CSS as the styling language, 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.

2.1.2 Features defined in other specifications

this section will be removed at some point

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

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

2.1.3 Common conformance requirements for APIs exposed to JavaScript

This section will eventually be removed in favour of WebIDL.

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

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

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

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

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

2.2 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).

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

xml

http://www.w3.org/XML/1998/namespace

html

http://www.w3.org/1999/xhtml

svg

http://www.w3.org/2000/svg

Attribute names are said to be XML-compatible if they match the Name production defined in XML, they contain no U+003A COLON (:) characters, and they do not start with three characters "xml". [XML]

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

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

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

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

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.

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.

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; specifically, any Node with node type TEXT_NODE (3) or CDATA_SECTION_NODE (4). [DOM3CORE]

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

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

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

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

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, albeit without letting the user interact with Web pages where that would involve invoking any script.

2.3 URLs

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

2.3.1 Terminology

A URL is a string used to identify a resource. A URL is always associated with a Document, either explicitly when the URL is created or defined; or through a DOM node, in which case the associated Document is the node's Document; or through a script, in which case the associated Document is the script's script document context.

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

• The URL is a valid URI reference [RFC3986].

• The URL is a valid IRI reference and it has no query component. [RFC3987]

• The URL is a valid IRI reference and its query component contains no unescaped non-ASCII characters. [RFC3987]

• The URL is a valid IRI reference and the character encoding of the URL's Document is UTF-8 or UTF-16. [RFC3987]

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

2.3.2 Parsing URLs

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

1. Strip leading and trailing space characters from url.

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

   • Add all characters with codepoints less than or equal to U+0020 or greater than or equal to U+007F to the <unreserved> production.
   • Add the characters U+0022, U+003C, U+003E, U+005B .. U+005E, U+0060, and U+007B .. U+007D to the <unreserved> production.
   • Add a single U+0025 PERCENT SIGN character as a second alternative way of matching the <pct-encoded> production, except when the <pct-encoded> is used in the <reg-name> production.
   • Add the U+0023 NUMBER SIGN character to the characters allowed in the <fragment> production.

3. If url doesn't match the <URI-reference> production, even after the above changes are made to the ABNF definitions, then parsing the URL fails with an error. [RFC3986]

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

   <scheme>

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

   <host>

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

   <port>

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

   <hostport>

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

   <path>

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

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

   <query>

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

   <fragment>

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

2.3.3 Resolving URLs

Relative URLs are resolved relative to a base URL. The base URL of a URL is the absolute URL obtained as follows:

If the URL to be resolved was passed to an API

The base URL is the document base URL of the script's script document context.

If the URL to be resolved is from the value of a content attribute

The base URL is the base URI of the element that the attribute is on, as defined by the XML Base specification, with the base URI of the document entity being defined as the document base URL of the Document that owns the element.

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

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

If the URL to be resolved was found in an offline application cache manifest

The base URL is the URL of the application cache manifest.

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

1. If there is no base element that is both a child of the head element and has an href attribute, then the document base URL is the document's address.

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

3. Resolve the url URL, using the document's address as the base URL (thus, the base href attribute isn't affect by xml:base attributes).

4. The document base URL is the result of the previous step if it was successful; otherwise it is the document's address.

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

1. Let url be the URL being resolved.

2. Let document be the Document associated with url.

3. Let encoding be the character encoding of document.

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

5. Let base be the base URL for url. (This is an absolute URL.)

6. Parse url into its component parts.

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

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

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

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

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

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

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

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

   1. If the character in question cannot be expressed in the encoding encoding, then replace it with a single 0x3F octet (an ASCII question mark) and skip the remaining substeps for this character.
   2. Encode the character into a sequence of octets as defined by the encoding encoding.
   3. Replace the character with the percent-encoded form of those octets. [RFC3986]

10. Apply the algorithm described in RFC 3986 section 5.2 Relative Resolution, using url as the potentially relative URI reference (R), and base as the base URI (Base). [RFC3986]

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

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

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

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

14. Return result.

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

2.3.4 Dynamic changes to base URLs

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

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

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

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

If the element is a hyperlink element

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

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

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

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

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

Otherwise

The element is not directly affected.

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

2.3.5 Interfaces for URL manipulation

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

           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;

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

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

The seven URL decomposition attributes have similar requirements.

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

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

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

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

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

2.4 Common microsyntaxes

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

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

2.4.1 Common parser idioms

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

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]

2.4.2 Boolean attributes

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

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

2.4.3 Numbers

2.4.3.1. 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.

2.4.3.2. 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.

2.4.3.3. 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.

2.4.3.4. 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 guaranteed to be a valid floating point number).
6. Return number.

2.4.3.5. 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)

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

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

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

7. Let negated be false.

8. Let value be 0.

9. Let started be false. This variable is set to true when the parser sees a number or a "-" character.

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

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

12. Let bogus be false.

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

    A U+002D HYPHEN-MINUS character

    Follow these substeps:

    1. If got number is true, let finished be true.
    2. If finished is true, skip to the next step in the overall set of steps.
    3. If started is true, let negated be false.
    4. Otherwise, if started is false and if bogus is false, let negated be true.
    5. Let started be true.

    A character in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. Multiply value by ten.
    3. Add the value of the digit, interpreted in base ten, to value.
    4. Let started be true.
    5. Let got number be true.

    A U+0020 SPACE character

    A U+002C COMMA character

    A U+003B SEMICOLON character

    Follow these substeps:

    1. If got number is false, return the numbers list and abort. This happens if an entry in the list has no digits, as in "1,2,x,4".
    2. If negated is true, then negate value.
    3. Append value to the numbers list.
    4. Jump to step 4 in the overall set of steps.

    A U+002E FULL STOP character

    Follow these substeps:

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

    Any other character

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. Let negated be false.
    3. Let bogus be true.
    4. If started is true, then return the numbers list, and abort. (The value in value is not appended to the list first; it is dropped.)

14. Advance position to the next character in input, or to beyond the end of the string if there are no more characters.

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

16. If negated is true, then negate value.

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

18. Return the numbers list and abort.

2.4.4 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]

2.4.4.1. 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.

2.4.4.2. 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 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 might 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).

2.4.5 Time offsets

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

2.4.6 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.

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

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

1. Let input be the string being parsed.

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

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

4. Skip whitespace

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

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

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

   3. Skip whitespace

6. Return tokens.

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

1. Let input be the string being modified.

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

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

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

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

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

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

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

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

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

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

   1. Skip whitespace (in input).

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

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

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

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

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

2.4.7 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 be ignored.

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

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

2.4.8 References

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

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

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

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

3. Return the first element of type type that has an id or name attribute whose value case-insensitively matches s.

2.5 Common DOM interfaces

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

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

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

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

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

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

If a reflecting DOM attribute is an unsigned integer type (unsigned long) then, on getting, the content attribute must be parsed according to the rules for parsing unsigned integers, and if that is successful, the resulting value must be returned. If, on the other hand, it 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 the shortest possible string representing the number as a valid non-negative integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is an unsigned integer type (unsigned long) that is limited to only positive non-zero numbers, then the behavior is similar to the previous case, but zero is not allowed. On getting, the content attribute must first be parsed according to the rules for parsing unsigned integers, and if that is successful, the resulting value must be returned. If, on the other hand, it 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 the shortest possible string representing the number as a valid non-negative integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is a floating point number type (float) and the content attribute is defined to contain a time offset, then, on getting, the content attribute must be parsed according to the rules for parsing time offsets, and if that is successful, the resulting value, in seconds, must be returned. If that fails, or if the attribute is absent, the default value must be returned, or the not-a-number value (NaN) if there is no default value. On setting, the given value, interpreted as a time offset in seconds, must be converted to a string using the time offset serialization rules, and that string must be used as the new content attribute value.

If a reflecting DOM attribute is a floating point number type (float) and it doesn't fall into one of the earlier categories, then, on getting, the content attribute must be parsed according to the rules for parsing floating point number values, and if that is successful, the resulting value must be returned. If, on the other hand, it fails, or if the attribute is absent, the default value must be returned instead, or 0.0 if there is no default value. On setting, the given value must be converted to the shortest possible string representing the number as a valid floating point number in base ten and then 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 content attribute must itself be immediately mutated. When the attribute is absent, then the string represented by the DOMTokenList object is the empty string; when the object mutates this empty string, the user agent must first add the corresponding content attribute, and then mutate that attribute instead. DOMTokenList attributes are always read-only. The same DOMTokenList object must be returned every time for each attribute.

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

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

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

2.5.2 Collections

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

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

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

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

The rows list is not in tree order.

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

2.5.2.1. HTMLCollection

The HTMLCollection interface represents a generic collection of elements.

interface HTMLCollection {
  readonly attribute unsigned long length;
  [IndexGetter] Element item(in unsigned long index);
  [NameGetter] 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.

2.5.2.2. HTMLFormControlsCollection

The HTMLFormControlsCollection interface represents a collection of form controls.

interface HTMLFormControlsCollection {
  readonly attribute unsigned long length;
  [IndexGetter] HTMLElement item(in unsigned long index);
  [NameGetter] 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.

2.5.2.3. HTMLOptionsCollection

The HTMLOptionsCollection interface represents a list of option elements.

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

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

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

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

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

The 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.

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.

2.5.3 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).

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

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.

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

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

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

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

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

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

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

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

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

2.5.4 DOMStringMap

The DOMStringMap interface represents a set of name-value pairs. When a DOMStringMap object is instanced, it is associated with three algorithms, one for getting values from names, one for setting names to certain values, and one for deleting names.

The names of the methods on this interface are temporary and will be fixed when the Web IDL / "Language Bindings for DOM Specifications" spec is ready to handle this case.

interface DOMStringMap {
  [NameGetter] DOMString XXX1(in DOMString name); 
  [NameSetter] void XXX2(in DOMString name, in DOMString value); 
  [XXX] boolean XXX3(in DOMString name); 
};

The XXX1(name) method must call the algorithm for getting values from names, passing name as the name, and must return the corresponding value, or null if name has no corresponding value.

The XXX2(name, value) method must call the algorithm for setting names to certain values, passing name as the name and value as the value.

The XXX3(name) method must call the algorithm for deleting names, passing name as the name, and must return true.

2.5.5 DOM feature strings

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

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

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

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

2.6 Fetching resources

replace all instances of the word 'fetch' or 'download' with a reference to this section, and put something here that talks about caching, that redirects to the offline storage stuff when appropriate, that defines that before fetching a URL you have to resolve the URL, so that every case of fetching doesn't have to independently say to resolve the URL, etc; "once fetched, a resource might have to have its type determined", pointing to the next section but also explicitly saying that it's up to the part of the spec doing the fetching to determine how the type is established

2.7 Determining the type of a resource

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

2.7.1 Content-Type metadata

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

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

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

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

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

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

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

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

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

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

5. Process the next character as follows:

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

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

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

   If it is an unmatched U+0022 QUOTATION MARK ('"')

   If it is an unmatched U+0027 APOSTROPHE ("'")

   If there is no next character

   Return nothing.

   Otherwise

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

The above algorithm is a willful violation of the HTTP specification. [RFC2616]

2.7.2 Content-Type sniffing: Web pages

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

1. Let official type be the type given by the Content-Type metadata for the resource (in lowercase, ignoring any parameters). If there is no such type, jump to the unknown type step below.

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

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

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

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

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

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

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

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

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

2.7.3 Content-Type sniffing: text or binary

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

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

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

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

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

4. Otherwise, if any of the first n bytes of the resource are in one of the following byte ranges:

   • 0x00 - 0x08
   • 0x0B
   • 0x0E - 0x1A
   • 0x1C - 0x1F

   ...then the sniffed type of the resource is "application/octet-stream".

   maybe we should invoke the "Content-Type sniffing: image" section now, falling back on "application/octet-stream".

5. Otherwise, the sniffed type of the resource is "text/plain".

2.7.4 Content-Type sniffing: unknown type

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

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

3. For each row in the table below:

   If the row has no "WS" bytes:

   1. Let pattern length be the length of the pattern (number of bytes described by the cell in the second column of the row).
   2. If pattern length is smaller than stream length then skip this row.
   3. Apply the "and" operator to the first pattern length bytes of the resource and the given mask (the bytes in the cell of first column of that row), and let the result be the data.
   4. If the bytes of the data matches the given pattern bytes exactly, then the sniffed type of the resource is the type given in the cell of the third column in that row; abort these steps.

   If the row has a "WS" byte:

   1. Let index_pattern be an index into the mask and pattern byte strings of the row.

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

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

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

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

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

      Otherwise, increment index_pattern to the next byte in the mask and pattern and index_stream to the next byte in the byte stream.

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

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

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

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

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

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

4. As a last-ditch effort, jump to the text or binary section.

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

2.7.5 Content-Type sniffing: image

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

User agents must ignore any rows for image types that they do not support.

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

2.7.6 Content-Type sniffing: feed or HTML

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

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

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

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

4. Initialise pos to 0.

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

6. Loop start: Examine s[pos].

   If it is 0x09 (ASCII tab), 0x20 (ASCII space), 0x0A (ASCII LF), or 0x0D (ASCII CR)

   Increase pos by 1 and repeat this step.

   If it is 0x3C (ASCII "<")

   Increase pos by 1 and go to the next step.

   If it is anything else

   The sniffed type of the resource is "text/html". Abort these steps.

7. If the bytes with positions pos to pos+2 in s are exactly equal to 0x21, 0x2D, 0x2D respectively (ASCII for "!--"), then:

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

8. If s[pos] is 0x21 (ASCII "!"):

   1. Increase pos by 1.
   2. If s[pos] equal 0x3E, then increase pos by 1 and jump back to the step labeled loop start in the overall algorithm in this section.
   3. Otherwise, return to step 1 in these substeps.

9. If s[pos] is 0x3F (ASCII "?"):

   1. Increase pos by 1.
   2. If s[pos] and s[pos+1] equal 0x3F and 0x3E respectively, then increase pos by 1 and jump back to the step labeled loop start in the overall algorithm in this section.
   3. Otherwise, return to step 1 in these substeps.

10. Otherwise, if the bytes in s starting at pos match any of the sequences of bytes in the first column of the following table, then the user agent must follow the steps given in the corresponding cell in the second column of the same row.

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

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

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

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

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

3. Semantics and structure of HTML documents

3.1 Introduction

This section is non-normative.

An introduction to marking up a document.

3.2 Documents

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

3.2.1 Documents in the DOM

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

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

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
  [PutForwards=href] readonly attribute Location location;
  readonly attribute DOMString URL;
           attribute DOMString domain;
  readonly attribute DOMString referrer;
           attribute DOMString cookie;
  readonly attribute DOMString lastModified;
  readonly attribute DOMString compatMode;
           attribute DOMString charset;
  readonly attribute DOMString characterSet;
  readonly attribute DOMString defaultCharset;
  readonly attribute DOMString readyState;

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

  // dynamic markup insertion
           attribute DOMString innerHTML;
  HTMLDocument open();
  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);

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

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

3.2.2 Security

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

3.2.3 Resource metadata management

The URL attribute must return the document's address.

The referrer attribute must return either the address of the active document of the source browsing context at the time the navigation was started (that is, the page which navigated the browsing context to the current document), or the empty string if there is no such originating page, or if the UA has been configured not to report referrers in this case, or if the navigation was initiated for a hyperlink with a noreferrer keyword.

In the case of HTTP, the referrer DOM attribute will match the Referer (sic) header that was sent when fetching the current page.

Typically user agents are configured to not report referrers in the case where the referrer uses an encrypted protocol and the current page does not (e.g. when navigating from an https: page to an http: page).

The cookie attribute represents the cookies of the resource.

On getting, if the sandboxed origin browsing context flag is set on the browsing context of the document, the user agent must raise a security exception. Otherwise, it must return the same string as the value of the Cookie HTTP header it would include if fetching the resource indicated by the document's address over HTTP, as per RFC 2109 section 4.3.4 or later specifications. [RFC2109] [RFC2965]

On setting, if the sandboxed origin browsing context flag is set on the browsing context of the document, the user agent must raise a security exception. Otherwise, the user agent must act as it would when processing cookies if it had just attempted to fetch the document's address over HTTP, and had received a response with a Set-Cookie header whose value was the specified value, as per RFC 2109 sections 4.3.1, 4.3.2, and 4.3.3 or later specifications. [RFC2109] [RFC2965]

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 file system 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.

A Document is always set to one of three modes: no quirks mode, the default; quirks mode, used typically for legacy documents; and limited quirks mode, also known as "almost standards" mode. The mode is only ever changed from the default by the HTML parser, based on the presence, absence, or value of the DOCTYPE string.

The compatMode DOM attribute must return the literal string "CSS1Compat" unless the document has been set to quirks mode by the HTML parser, in which case it must instead return the literal string "BackCompat".

Documents have an associated character encoding. When a Document object is created, the document's character encoding must be initialized to UTF-16. Various algorithms during page loading affect this value, as does the charset setter. [IANACHARSET]

The charset DOM attribute must, on getting, return the preferred MIME name of the document's character encoding. On setting, if the new value is an IANA-registered alias for a character encoding, the document's character encoding must be set to that character encoding. (Otherwise, nothing happens.)

The characterSet DOM attribute must, on getting, return the preferred MIME name of the document's character encoding.

The defaultCharset DOM attribute must, on getting, return the preferred MIME name of a character encoding, possibly the user's default encoding, or an encoding associated with the user's current geographical location, or any arbitrary encoding name.

Each document has a current document readiness. When a Document object is created, it must have its current document readiness set to the string "loading". Various algorithms during page loading affect this value. When the value is set, the user agent must fire a simple event called readystatechanged at the Document object.

The readyState DOM attribute must, on getting, return the current document readiness.

3.2.4 DOM tree accessors

The html element of a document is the document's root element, if there is one and it's an html element, or null otherwise.

The head element of a document is the first head element that is a child of the html element, if there is one, or null otherwise.

The title element of a document is the first title element in the document (in tree order), if there is one, or null otherwise.

The title attribute must, on getting, run the following algorithm:

1. If the root element is an svg element in the "http://www.w3.org/2000/svg" namespace, and the user agent supports SVG, then the getter must return the value that would have been returned by the DOM attribute of the same name on the SVGDocument interface.

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 title element is null and the head element is null, then the attribute must do nothing. Stop the algorithm here.
3. If the title element is null, then a new title element must be created and appended to the head element.
4. The children of the title element (if any) must all be removed.
5. A single Text node whose data is the new value being assigned must be appended to the title element.

The title attribute on the HTMLDocument interface should shadow the attribute of the same name on the SVGDocument interface when the user agent supports both HTML and SVG.

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 embeds attribute must return an HTMLCollection rooted at the Document node, whose filter matches only embed elements.

The plugins attribute must return the same object as that returned by the embeds attribute.

The links attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with href attributes and area elements with href attributes.

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

The anchors attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with name attributes.

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

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 labeled 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.

3.3 Elements

3.3.1 Semantics

Elements, attributes, and attribute values in HTML are defined (by this specification) to have certain meanings (semantics). For example, the ol element represents an ordered list, and the lang attribute represents the language of the content.

Authors must not use elements, attributes, and attribute values for purposes other than their appropriate intended semantic purpose.

<!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/">Ernest</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 Elements in the DOM

The nodes representing HTML elements in the DOM must implement, and expose to scripts, the interfaces listed for them in the relevant sections of this specification. This includes HTML elements in XML documents, even when those documents are in another context (e.g. inside an XSLT transform).

Elements in the DOM represent things; that is, they have intrinsic meaning, also known as semantics.

For example, an ol element represents an ordered list.

The basic interface, from which all the HTML elements' interfaces inherit, and which must be used by elements that have no additional requirements, is the HTMLElement interface.

interface HTMLElement : Element {
  // DOM tree accessors
  NodeList getElementsByClassName(in DOMString classNames);

  // dynamic markup insertion
           attribute DOMString innerHTML;

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

  // user interaction
           attribute boolean irrelevant;
  void click();
  void scrollIntoView();
  void scrollIntoView(in boolean top);
           attribute long tabIndex;
  void focus();
  void blur();
           attribute boolean draggable;
           attribute DOMString contentEditable;
  readonly attribute DOMString isContentEditable;
           attribute HTMLMenuElement contextMenu;

  // styling
  readonly attribute CSSStyleDeclaration style;

  // 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 onstorage;
           attribute EventListener onsubmit;
           attribute EventListener onunload;

};

The HTMLElement interface holds methods and attributes related to a number of disparate features, and the members of this interface are therefore described in various different sections of this specification.

3.3.3 Global attributes

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

Global attributes:

class

contenteditable

contextmenu

dir

draggable

id

irrelevant

lang

ref

registrationmark

style

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

onstorage

onsubmit

onunload

Also, custom data attributes (e.g. data-foldername or data-msgid) can be specified on any HTML element, to store custom data specific to the page.

In HTML documents, elements in the HTML namespace may have an xmlns attribute specified, if, and only if, it has the exact value "http://www.w3.org/1999/xhtml". This does not apply to XML documents.

In HTML, the xmlns attribute has absolutely no effect. It is basically a talisman. It is allowed merely to make migration to and from XHTML mildly easier. When parsed by an HTML parser, the attribute ends up in no namespace, not the "http://www.w3.org/2000/xmlns/" namespace like namespace declaration attributes in XML do.

In XML, an xmlns attribute is part of the namespace declaration mechanism, and an element cannot actually have an xmlns attribute in no namespace specified.

3.3.3.1. The id attribute

The id attribute represents its element's unique identifier. The value must be unique in the 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.

3.3.3.2. The title attribute

The title attribute represents advisory information for the element, such as would be appropriate for a tooltip. On a link, this could be the title or a description of the target resource; on an image, it could be the image credit or a description of the image; on a paragraph, it could be a footnote or commentary on the text; on a citation, it could be further information about the source; and so forth. The value is text.

If this attribute is omitted from an element, then it implies that the title attribute of the nearest ancestor HTML element with a title attribute set is also relevant to this element. Setting the attribute overrides this, explicitly stating that the advisory information of any ancestors is not relevant to this element. Setting the attribute to the empty string indicates that the element has no advisory information.

If the title attribute's value contains U+000A LINE FEED (LF) characters, the content is split into multiple lines. Each U+000A LINE FEED (LF) character represents a line break.

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

The title DOM attribute must reflect the title content attribute.

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

The xml:lang attribute may 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 pronunciations, or for dictionary selection).

The lang DOM attribute must reflect the lang content attribute.

3.3.3.4. The xml:base attribute (XML only)

The xml:base attribute is defined in XML Base. [XMLBASE]

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

3.3.3.5. The dir attribute

The dir attribute specifies the element's text directionality. The attribute is an enumerated attribute with the keyword ltr mapping to the state ltr, and the keyword rtl mapping to the state rtl. The attribute has no defaults.

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 element, or ltr if there is no parent element.

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.

3.3.3.6. The class attribute

Every HTML element may have a class attribute specified.

The attribute, if specified, must have a value that is an unordered set of unique space-separated tokens representing the various classes that the element belongs to.

The classes that an HTML element has assigned to it consists of all the classes returned when the value of the class attribute is split on spaces.

Assigning classes to an element affects class matching in selectors in CSS, the getElementsByClassName() method in the DOM, and other such features.

Authors may use any value in the class attribute, but are encouraged to use the values that describe the nature of the content, rather than values that describe the desired presentation of the content.

The className and classList DOM attributes must both reflect the class content attribute.

3.3.3.7. The style attribute

All elements may have the style content attribute set. If specified, the attribute must contain only a list of zero or more semicolon-separated (;) CSS declarations. [CSS21]

The attribute, if specified, must be parsed and treated as the body (the part inside the curly brackets) of a declaration block in a rule whose selector matches just the element on which the attribute is set. For the purposes of the CSS cascade, the attribute must be considered to be a 'style' attribute at the author level.

Documents that use style attributes on any of their elements must still be comprehensible and usable if those attributes were removed.

In particular, using the style attribute to hide and show content, or to convey meaning that is otherwise not included in the document, is non-conforming.

The style DOM attribute must return a CSSStyleDeclaration whose value represents the declarations specified in the attribute, if present. Mutating the CSSStyleDeclaration object must create a style attribute on the element (if there isn't one already) and then change its value to be a value representing the serialized form of the CSSStyleDeclaration object. [CSSOM]

<p>My sweat suit is <span style="color: green; background:
transparent">green</span> and my eyes are <span style="color: blue;
background: transparent">blue</span>.</p>

3.3.3.8. Embedding custom non-visible data

A custom data attribute is an attribute whose name starts with the string "data-", has at least one character after the hyphen, is XML-compatible, and has no namespace.

Custom data attributes are intended to store custom data private to the page or application, for which there are no more appropriate attributes or elements.

Every HTML element may have any number of custom data attributes specified, with any value.

The dataset DOM attribute provides convenient accessors for all the data-* attributes on an element. On getting, the dataset DOM attribute must return a DOMStringMap object, associated with the following three algorithms, which expose these attributes on their element:

The algorithm for getting values from names

1. Let name be the concatenation of the string data- and the name passed to the algorithm.
2. If the element does not have an attribute with the name name, then the name has no corresponding value, abort.
3. Otherwise, return the value of the attribute with the name name.

The algorithm for setting names to certain values

1. Let name be the concatenation of the string data- and the name passed to the algorithm.
2. Let value be the value passed to the algorithm.
3. Set the value of the attribute with the name name, to the value value, replacing any previous value if the attribute already existed. If setAttribute() would have raised an exception when setting an attribute with the name name, then this must raise the same exception.

The algorithm for deleting names

1. Let name be the concatenation of the string data- and the name passed to the algorithm.
2. Remove the attribute with the name name, if such an attribute exists. Do nothing otherwise.

<div class="spaceship" data-id="92432"
     data-weapons="laser 2" data-shields="50%"
     data-x="30" data-y="10" data-z="90">
 <button class="fire"
         onclick="spaceships[this.parentNode.dataset.id].fire()">
  Fire
 </button>
</div>

Authors should carefully design such extensions so that when the attributes are ignored and any associated CSS dropped, the page is still usable.

User agents must not derive any implementation behavior from these attributes or values. Specifications intended for user agents must not define these attributes to have any meaningful values.

3.4 Content models

All the elements in this specification have a defined content model, which describes what nodes are allowed inside the elements, and thus what the structure of an HTML document or fragment must look like.

As noted in the conformance and terminology sections, for the purposes of determining if an element matches its content model or not, CDATASection nodes in the DOM are treated as equivalent to Text nodes, and entity reference nodes are treated as if they were expanded in place.

The space characters are always allowed between elements. User agents represent these characters between elements in the source markup as text nodes in the DOM. Empty text nodes and text nodes consisting of just sequences of those characters are considered inter-element whitespace.

Inter-element whitespace, comment nodes, and processing instruction nodes must be ignored when establishing whether an element matches its content model or not, and must be ignored when following algorithms that define document and element semantics.

An element A is said to be preceded or followed by a second element B if A and B have the same parent node and there are no other element nodes or text nodes (other than inter-element whitespace) between them.

Authors must not use elements in the HTML namespace anywhere except where they are explicitly allowed, as defined for each element, or as explicitly required by other specifications. For XML compound documents, these contexts could be inside elements from other namespaces, if those elements are defined as providing the relevant contexts.

In addition, elements in the HTML namespace may be orphan nodes (i.e. without a parent node).

var data = {
  name: "Banana",
  cell: document.createElement('td'), 
};

3.4.1 Kinds of content

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

• Metadata content
• Flow 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.

3.4.1.1. Metadata content

Metadata content is content that sets up the presentation or behavior of the rest of the content, or that sets up the relationship of the document with other documents, or that conveys other "out of band" information.

Elements from other namespaces whose semantics are primarily metadata-related (e.g. RDF) are also metadata content.

3.4.1.2. Flow content

Most elements that are used in the body of documents and applications are categorized as flow content.

As a general rule, elements whose content model allows any flow content should have either at least one descendant text node that is not inter-element whitespace, or at least one descendant element node that is embedded content. For the purposes of this requirement, del elements and their descendants must not be counted as contributing to the ancestors of the del element.

This requirement is not a hard requirement, however, as there are many cases where an element can be empty legitimately, for example when it is used as a placeholder which will later be filled in by a script, or when the element is part of a template and would on most pages be filled in but on some pages is not relevant.

3.4.1.3. Sectioning content

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

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

3.4.1.4. Heading content

Heading content defines the header of a section (whether explicitly marked up using sectioning content elements, or implied by the heading content itself).

3.4.1.5. Phrasing content

Phrasing content is the text of the document, as well as elements that mark up that text at the intra-paragraph level. Runs of phrasing content form paragraphs.

All phrasing content is also flow content. Any content model that expects flow 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 categorized as phrasing content can only contain elements that are themselves categorized as phrasing content, not any flow content.

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

3.4.1.6. Embedded content

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

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

3.4.1.7. 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.

3.4.2 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 not contain content that would not 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 flow content.

3.5 Paragraphs

A paragraph is typically a block of text with one or more sentences that discuss a particular topic, as in typography, but can also be used for more general thematic grouping. For instance, an address is also a paragraph, as is a part of a form, a byline, or a stanza in a poem.

Paragraphs in flow content are defined relative to what the document looks like without the 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>

3.6 APIs in HTML documents

For HTML documents, and for HTML elements in HTML documents, certain APIs defined in DOM3 Core become case-insensitive or case-changing, as sometimes defined in DOM3 Core, and as summarized or required below. [DOM3CORE].

This does not apply to XML documents or to elements that are not in the HTML namespace despite being in HTML documents.

Element.tagName, 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.

3.7 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 behavior 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).

3.7.1 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, reset timers, empty event queue, kill any pending transactions, XMLHttpRequests, etc

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. Change the document's character encoding to UTF-16.

8. 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).

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

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

11. 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.)

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

13. 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.

3.7.2 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 pending external script, 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 serialization 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 serialization 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 element, 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.

3.7.3 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 must return a string in the form of an internal general parsed entity, and on HTMLDocuments must return a string in the form of a document entity. The string returned must be XML namespace-well-formed and must be an isomorphic serialization of all of that node's child nodes, in document order. User agents may adjust prefixes and namespace declarations in the serialization (and indeed might be forced to do so in some cases to obtain namespace-well-formed XML). For the innerHTML attribute on HTMLElement objects, if any of the elements in the serialization are in no namespace, the default namespace in scope for those elements must be explicitly declared as the empty string. (This doesn't apply to the innerHTML attribute on HTMLDocument objects.) [XML] [XMLNS]

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

• A Document node with no child element nodes.
• 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 (":").
• An Attr node, Text node, CDATASection node, Comment node, or ProcessingInstruction 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 unserializable. The DOM enforces all the other XML constraints; for example, trying to set an attribute with a name that contains an equals sign (=) will raised an INVALID_CHARACTER_ERR exception.

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 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.

4. The elements of HTML

4.1 The root element

4.1.1 The html element

Categories

None.

Contexts in which this element may be used:

As the root element of a document.

Wherever a subdocument fragment is allowed in a compound document.

Content model:

A head element followed by a body element.

Element-specific attributes:

manifest

DOM interface:

Uses HTMLElement.

The html element represents the root of an HTML document.

The manifest attribute gives the address of the document's application cache manifest, if there is one. If the attribute is present, the attribute's value must be a valid URL.

The manifest attribute only has an effect during the early stages of document load. Changing the attribute dynamically thus has no effect (and thus, no DOM API is provided for this attribute).

Later base elements don't affect the resolving of relative URLs in manifest attributes, as the attributes are processed before those elements are seen.

4.2 Document metadata

4.2.1 The head element

Categories

None.

Contexts in which this element may be used:

As the first element in an html element.

Content model:

One or more elements of metadata content, of which exactly one is a title element.

Element-specific attributes:

None.

DOM interface:

Uses HTMLElement.

The head element collects the document's metadata.

4.2.2 The title element

Categories

Metadata content.

Contexts in which this element may be used:

In a head element containing no other title elements.

Content model:

Text.

Element-specific attributes:

None.

DOM interface:

Uses HTMLElement.

The title element represents the document's title or name. Authors should use titles that identify their documents even when they are used out of context, for example in a user's history or bookmarks, or in search results. The document's title is often different from its first 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.

4.2.3 The base element

Categories

Metadata content.

Contexts in which this element may be used:

In a head element containing no other base elements.

Content model:

Empty.

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 base URL for the purposes of resolving relative URLs, 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 valid URL.

A base element, if it has an href attribute, must come before any other elements in the tree that have attributes defined as taking URLs, except the html element (its manifest attribute isn't affected by base elements).

If there are multiple base elements with href attributes, all but the first are ignored.

The target attribute, if specified, must contain a valid browsing context name or keyword. 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.

If there are multiple base elements with target attributes, all but the first are ignored.

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

4.2.4 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

sizes

Also, the title attribute has special semantics on this element.

DOM interface:

interface HTMLLinkElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString href;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
           attribute DOMString sizes;
};

The LinkStyle interface must also be implemented by this element, the styling processing model defines how. [CSSOM]

The link element allows authors to link their document to other resources.

The destination of the link is given by the href attribute, which must be present and must contain a valid URL. If the href attribute is absent, then the element does not define a link.

The 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); exactly which and how many links are created depends on the keywords given in the rel attribute. User agents must process the links on a per-link basis, not a per-element basis.

The exact behavior for links to external resources depends on the exact relationship, as defined for the relevant link type. Some of the attributes control whether or not the external resource is to be applied (as defined below). For external resources that are represented in the DOM (for example, style sheets), the DOM representation must be made available even if the resource is not applied. (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.)

HTTP semantics must be followed when fetching external resources. (For example, redirects must be followed and 404 responses must cause the external resource to not be applied.)

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 address 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).

Hyperlinks created with the link element and its rel attribute apply to the whole page. This contrasts with the rel attribute of a and area elements, which indicates the type of a link whose context is given by the link's location within the document.

The media attribute says which media the resource applies to. The value must be a valid media query. [MQ]

If the link is a hyperlink then the media attribute is purely advisory, and describes for which media the document in question was designed.

However, if the link is an external resource link, then the media attribute is prescriptive. The user agent must apply the external resource to views while their state match the listed media and the other relevant conditions apply, and must not apply them otherwise.

The default, if the media attribute is omitted, is all, meaning that by default links apply to all media.

The hreflang attribute on the link element has the same semantics as the hreflang attribute on hyperlink elements.

The type attribute gives the MIME type of the linked resource. It is purely advisory. The value must be a valid MIME type, optionally with parameters. [RFC2046]

For external resource links, the type attribute is used as a hint to user agents so that they can avoid downloading resources they do not support. If the attribute is present, then the user agent must assume that the resource is of the given type. If the attribute is omitted, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type. If the UA does not support the given MIME type for the given link relationship, then the UA should not download the resource; if the UA does support the given MIME type for the given link relationship, then the UA should download the resource. If the attribute is omitted, and the external resource link type does not have a default type defined, but the user agent would fetch the resource if the type was known and supported, then the user agent should fetch the resource under the assumption that it will be supported.

User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use the type attribute to determine its actual type. Only the actual type (as defined in the next paragraph) is used to determine whether to apply the resource, not the aforementioned assumed type.

If the resource is expected to be an image, user agents may apply the image sniffing rules, with the official type being the type determined from the resource's Content-Type metadata, and use the resulting sniffed type of the resource as if it was the actual type. Otherwise, if the resource is not expected to be an image, or if the user agent opts not to apply those rules, then the user agent must use the resource's Content-Type metadata to determine the type of the resource. If there is no type metadata, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type.

Once the user agent has established the type of the resource, the user agent must apply the resource if it is of a supported type and the other relevant conditions apply, and must ignore the resource otherwise.

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

The sizes attribute is used with the icon link type. The attribute must not be specified on link elements that do not have a rel attribute that specifies the icon keyword.

Some versions of HTTP defined a Link: header, to be processed like a series of link elements. If supported, for the purposes of ordering links defined by HTTP headers must be assumed to come before any links in the document, in the order that they were given in the HTTP entity header. (URIs in these headers are to be processed and resolved according to the rules given in HTTP; the rules of this specification don't apply.) [RFC2616] [RFC2068]

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

The DOM attribute relList must reflect the rel content attribute.

The DOM attribute disabled only applies to style sheet links. When the link element defines a style sheet link, then the disabled attribute behaves as defined for the alternative style sheets DOM. For all other link elements it always return false and does nothing on setting.

4.2.5 The meta element

Categories

Metadata content.

Contexts in which this element may be used:

If the charset attribute is present, or if the element is in the Encoding declaration state: as the first element in a head element.

If the http-equiv attribute is present, and the element is not in the Encoding declaration state: in a head element.

If the http-equiv attribute is present, and the element is not in the Encoding declaration state: in a noscript element that is a child of a head element.

If the name attribute is present: where metadata content is expected.

Content model:

Empty.

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 serialized to string form (e.g. for transmission over the network or for disk storage) with the charset attribute.

Exactly one of the name, http-equiv, and charset attributes must be specified.

If either name or http-equiv is specified, then the content attribute must also be specified. Otherwise, it must be omitted.

The charset attribute specifies the character encoding used by the document. This is called a character encoding declaration.

The charset attribute may be specified in HTML documents only, 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.

4.2.5.1. Standard metadata names

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

application-name

The value must be a short free-form string that giving the name of the Web application that the page represents. If the page is not a Web application, the application-name metadata name must not be used. User agents may use the application name in UI in preference to the page's title, since the title might include status messages and the like relevant to the status of the page at a particular moment in time instead of just being the name of the application.

description

The value must be a free-form string that describes the page. The value must be appropriate for use in a directory of pages, e.g. in a search engine.

generator

The value must be a free-form string that identifies the software used to generate the document. This value must not be used on hand-authored pages.

4.2.5.2. Other metadata names

Extensions to the predefined set of metadata names may be registered in the WHATTF Wiki MetaExtensions page.

Anyone is free to edit the WHATTF 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 WHATTF Wiki MetaExtensions page to establish if a value not explicitly defined in this specification is allowed or not. When an author uses a new type not defined by either this specification or the Wiki page, conformance checkers should offer to add the value to the Wiki, with the details described above, with the "proposal" status.

This specification does not define how new values will get approved. It is expected that the Wiki will have a community that addresses this.

Metadata names whose values are to be URLs must not be proposed or accepted. Links must be represented using the link element, not the meta element.

4.2.5.3. Pragma directives

When the http-equiv attribute is specified on a meta element, the element is a pragma directive.

The http-equiv attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the rows with keywords give the states to which those keywords map.

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:

Encoding declaration state

The Encoding declaration state's user agent requirements are all handled by the parsing section of the specification. The state is just an alternative form of setting the charset attribute: it is a character encoding declaration.

For meta elements in the Encoding declaration state, the content attribute must have a value that is a case-insensitive match of a string that consists of the literal string "text/html;", optionally followed by any number of space characters, followed by the literal string "charset=", followed by the character encoding name of the character encoding declaration.

If the document contains a meta element in the Encoding declaration state then that element must be the first element in the document's head element, and the document must not contain a meta element with the charset attribute present.

The Encoding declaration state may be used in HTML documents only, elements in that state must not be used in XML documents.

Default style state

1. ...

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 URL. (For the purposes of determining the base URL, the url value comes from the value of a content attribute of the meta element.) If this fails, abort these steps.

22. Perform one or more of the following steps:

    • Set a timer so that in time seconds, adjusted to take into account user or user agent preferences, if the user has not canceled the redirect, the user agent navigates the document's browsing context to url, with replacement enabled, and with the document's browsing context as the source browsing context.

    • Provide the user with an interface that, when selected, navigates a browsing context to url, with the document's browsing context as the source browsing context.

    • Do nothing.

    In addition, the user agent may, as with anything, inform the user of any and all aspects of its operation, including the state of any timers, the destinations of any timed redirects, and so forth.

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

• 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 URL.

In the former case, the integer represents a number of seconds before the page is to be reloaded; in the latter case the integer represents a number of seconds before the page is to be replaced by the page at the given URL.

There must not be more than one meta element with any particular state in the document at a time.

4.2.5.4. Specifying the document's character encoding

A character encoding declaration is a mechanism by which the character encoding used to store or transmit a document is specified.

The following restrictions apply to character encoding declarations:

• The character encoding name given must be the name of the character encoding used to serialize the file.
• The value must be a valid character encoding name, and must be the preferred name for that encoding. [IANACHARSET]
• The character encoding declaration must be serialized without the use of character references or character escapes 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 an ASCII-compatible character encoding, and, in addition, if that encoding isn't US-ASCII itself, then the encoding must be specified using a meta element with a charset attribute or a meta element in the Encoding declaration state.

If the document contains a meta element with a charset attribute or a meta element in the Encoding declaration state, then the character encoding used must be an ASCII-compatible character encoding.

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

Authors should not use JIS_X0212-1990, x-JIS0208, and encodings based on EBCDIC. Authors should not use UTF-32. Authors must not use the CESU-8, UTF-7, BOCU-1 and SCSU encodings. [CESU8] [UTF7] [BOCU1] [SCSU]

Authors are encouraged to use UTF-8. Conformance checkers may advise against authors using legacy encodings.

In XHTML, the XML declaration should be used for inline character encoding information, if necessary.

4.2.6 The style element

Categories

Metadata content.

If the scoped attribute is present: flow content.

Contexts in which this element may be used:

If the scoped attribute is absent: where metadata content is expected.

If the scoped attribute is absent: in a noscript element that is a child of a head element.

If the scoped attribute is present: where flow content is expected, but before any 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 apply the styles to views while their state match the listed media, and must not apply them otherwise. [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 apply the specified style information only to the style element's parent element (if any), and that element's child nodes. Otherwise, the specified styles must, if applied, be applied to the entire document.

The title attribute on style elements defines alternative style sheet sets. If the style element has no title attribute, then it has no title; the title attribute of ancestors does not apply to the style element.

The title attribute on style elements, like the title attribute on link elements, differs from the global title attribute in that a style block without a title does not inherit the title of the parent element: it merely has no title.

All descendant elements must be processed, according to their semantics, before the style element itself is evaluated. For styling languages that consist of pure text, user agents must evaluate style elements by passing the concatenation of the contents of all the text nodes that are direct children of the style element (not any other nodes such as comments or elements), in tree order, to the style system. For XML-based styling languages, user agents must pass all the 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.

4.2.7 Styling

The link and style elements can provide styling information for the user agent to use when rendering the document. The DOM Styling specification specifies what styling information is to be used by the user agent and how it is to be used. [CSSOM]

The style and link elements implement the LinkStyle interface. [CSSOM]

For style elements, if the user agent does not support the specified styling language, then the sheet attribute of the element's LinkStyle interface must return null. Similarly, link elements that do not represent external resource links that contribute to the styling processing model (i.e. that do not have a stylesheet keyword in their rel attribute), and link elements whose specified resource has not yet been 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 result of resolving the URL given by the element's href content attribute, or the empty string if that fails. For style elements, there is no location.

The intended destination media for style information (media DOM attribute)

The media must be the same as the value of the element's media content attribute.

The style sheet title (title DOM attribute)

The title must be the same as the value of the element's title content attribute. If the attribute is absent, then the style sheet does not have a title. The title is used for defining alternative style sheet sets.

The disabled DOM attribute on link and style elements must return false and do nothing on setting, if the sheet attribute of their LinkStyle interface is null. Otherwise, it must return the value of the StyleSheet interface's disabled attribute on getting, and forward the new value to that same attribute on setting.

4.3 Sections

Some elements, for example address elements, are scoped to their nearest ancestor sectioning content. For such elements x, the elements that apply to a sectioning content element e are all the x elements whose nearest sectioning content ancestor is e.

4.3.1 The body element

Categories

Sectioning content.

Contexts in which this element may be used:

As the second element in an html element.

Content model:

Flow content.

Element-specific attributes:

None.

DOM interface:

interface HTMLBodyElement : 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.

4.3.2 The section element

Categories

Flow content.

Sectioning content.

Contexts in which this element may be used:

Where flow content is expected.

Content model:

Flow content.

Element-specific attributes:

None.

DOM interface:

Uses HTMLElement.

The section element represents a generic document or application section. A section, in this context, is a thematic grouping of content, typically with a 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.

4.3.3 The nav element

Categories

Flow content.

Sectioning content.

Contexts in which this element may be used:

Where flow content is expected.

Content model:

Flow content.

Element-specific attributes:

None.

DOM interface:

Uses HTMLElement.

The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links. Not all groups of links on a page need to be in a nav element — only sections that consist of primary navigation blocks are appropriate for the nav element. In particular, it is common for footers to have a list of links to various key parts of a site, but the footer element is more appropriate in such cases.