Abstract

This specification defines the 5th major revision of the core language of the World Wide Web: the Hypertext Markup Language (HTML). In this version, new features are introduced to help Web application authors, new elements are introduced based on research into prevailing authoring practices, and special attention has been given to defining clear conformance criteria for user agents in an effort to improve interoperability.

Status of This document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the most recently formally published revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

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The working groups maintains a list of all bug reports that the editor has not yet tried to address and a list of issues for which the chairs have not yet declared a decision. The editor also maintains a list of all e-mails that he has not yet tried to address. These bugs, issues, and e-mails apply to multiple HTML-related specifications, not just this one.

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 Candidate Recommendation stage should join the aforementioned mailing lists and take part in the discussions.

The publication of this document by the W3C as a W3C Working Draft does not imply that all of the participants in the W3C HTML working group endorse the contents of the specification. Indeed, for any section of the specification, one can usually find many members of the working group or of the W3C as a whole who object strongly to the current text, the existence of the section at all, or the idea that the working group should even spend time discussing the concept of that section.

The latest stable version of the editor's draft of this specification is always available on the W3C CVS server and in the WHATWG Subversion repository. The latest editor's working copy (which may contain unfinished text in the process of being prepared) contains the latest draft text of this specification (amongst others). For more details, please see the WHATWG FAQ.

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The W3C HTML Working Group is the W3C working group responsible for this specification's progress along the W3C Recommendation track. This specification is the 24 June 2010 Working Draft snapshot.

Work on this specification is also done at the WHATWG. The W3C HTML working group actively pursues convergence with the WHATWG, as required by the W3C HTML working group charter.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

  1. 1 Introduction
    1. 1.1 Background
    2. 1.2 Audience
    3. 1.3 Scope
    4. 1.4 History
    5. 1.5 Design notes
      1. 1.5.1 Serializability of script execution
      2. 1.5.2 Compliance with other specifications
    6. 1.6 HTML vs XHTML
    7. 1.7 Structure of this specification
      1. 1.7.1 How to read this specification
      2. 1.7.2 Typographic conventions
    8. 1.8 A quick introduction to HTML
    9. 1.9 Conformance requirements for authors
      1. 1.9.1 Presentational markup
      2. 1.9.2 Syntax errors
      3. 1.9.3 Restrictions on content models and on attribute values
    10. 1.10 Recommended reading
  2. 2 Common infrastructure
    1. 2.1 Terminology
      1. 2.1.1 Resources
      2. 2.1.2 XML
      3. 2.1.3 DOM trees
      4. 2.1.4 Scripting
      5. 2.1.5 Plugins
      6. 2.1.6 Character encodings
    2. 2.2 Conformance requirements
      1. 2.2.1 Dependencies
      2. 2.2.2 Extensibility
    3. 2.3 Case-sensitivity and string comparison
    4. 2.4 Common microsyntaxes
      1. 2.4.1 Common parser idioms
      2. 2.4.2 Boolean attributes
      3. 2.4.3 Keywords and enumerated attributes
      4. 2.4.4 Numbers
        1. 2.4.4.1 Non-negative integers
        2. 2.4.4.2 Signed integers
        3. 2.4.4.3 Real numbers
        4. 2.4.4.4 Percentages and lengths
        5. 2.4.4.5 Lists of integers
        6. 2.4.4.6 Lists of dimensions
      5. 2.4.5 Dates and times
        1. 2.4.5.1 Months
        2. 2.4.5.2 Dates
        3. 2.4.5.3 Times
        4. 2.4.5.4 Local dates and times
        5. 2.4.5.5 Global dates and times
        6. 2.4.5.6 Weeks
        7. 2.4.5.7 Vaguer moments in time
      6. 2.4.6 Colors
      7. 2.4.7 Space-separated tokens
      8. 2.4.8 Comma-separated tokens
      9. 2.4.9 References
      10. 2.4.10 Media queries
    5. 2.5 URLs
      1. 2.5.1 Terminology
      2. 2.5.2 Dynamic changes to base URLs
      3. 2.5.3 Interfaces for URL manipulation
    6. 2.6 Fetching resources
      1. 2.6.1 Protocol concepts
      2. 2.6.2 Encrypted HTTP and related security concerns
      3. 2.6.3 Determining the type of a resource
    7. 2.7 Common DOM interfaces
      1. 2.7.1 Reflecting content attributes in IDL attributes
      2. 2.7.2 Collections
        1. 2.7.2.1 HTMLCollection
        2. 2.7.2.2 HTMLAllCollection
        3. 2.7.2.3 HTMLFormControlsCollection
        4. 2.7.2.4 HTMLOptionsCollection
      3. 2.7.3 DOMTokenList
      4. 2.7.4 DOMSettableTokenList
      5. 2.7.5 Safe passing of structured data
      6. 2.7.6 DOMStringMap
      7. 2.7.7 DOM feature strings
      8. 2.7.8 Exceptions
      9. 2.7.9 Garbage collection
    8. 2.8 Namespaces
  3. 3 Semantics, structure, and APIs of HTML documents
    1. 3.1 Documents
      1. 3.1.1 Documents in the DOM
      2. 3.1.2 Security
      3. 3.1.3 Resource metadata management
      4. 3.1.4 DOM tree accessors
      5. 3.1.5 Creating documents
    2. 3.2 Elements
      1. 3.2.1 Semantics
      2. 3.2.2 Elements in the DOM
      3. 3.2.3 Global attributes
        1. 3.2.3.1 The id attribute
        2. 3.2.3.2 The title attribute
        3. 3.2.3.3 The lang and xml:lang attributes
        4. 3.2.3.4 The xml:base attribute (XML only)
        5. 3.2.3.5 The dir attribute
        6. 3.2.3.6 The class attribute
        7. 3.2.3.7 The style attribute
        8. 3.2.3.8 Embedding custom non-visible data
      4. 3.2.4 Element definitions
        1. 3.2.4.1 Attributes
      5. 3.2.5 Content models
        1. 3.2.5.1 Kinds of content
          1. 3.2.5.1.1 Metadata content
          2. 3.2.5.1.2 Flow content
          3. 3.2.5.1.3 Sectioning content
          4. 3.2.5.1.4 Heading content
          5. 3.2.5.1.5 Phrasing content
          6. 3.2.5.1.6 Embedded content
          7. 3.2.5.1.7 Interactive content
        2. 3.2.5.2 Transparent content models
        3. 3.2.5.3 Paragraphs
      6. 3.2.6 Annotations for assistive technology products (ARIA)
    3. 3.3 APIs in HTML documents
    4. 3.4 Interactions with XPath and XSLT
    5. 3.5 Dynamic markup insertion
      1. 3.5.1 Opening the input stream
      2. 3.5.2 Closing the input stream
      3. 3.5.3 document.write()
      4. 3.5.4 document.writeln()
      5. 3.5.5 innerHTML
      6. 3.5.6 outerHTML
      7. 3.5.7 insertAdjacentHTML()
  4. 4 The elements of HTML
    1. 4.1 The root element
      1. 4.1.1 The html element
    2. 4.2 Document metadata
      1. 4.2.1 The head element
      2. 4.2.2 The title element
      3. 4.2.3 The base element
      4. 4.2.4 The link element
      5. 4.2.5 The meta element
        1. 4.2.5.1 Standard metadata names
        2. 4.2.5.2 Other metadata names
        3. 4.2.5.3 Pragma directives
        4. 4.2.5.4 Other pragma directives
        5. 4.2.5.5 Specifying the document's character encoding
      6. 4.2.6 The style element
      7. 4.2.7 Styling
    3. 4.3 Scripting
      1. 4.3.1 The script element
        1. 4.3.1.1 Scripting languages
        2. 4.3.1.2 Restrictions for contents of script elements
        3. 4.3.1.3 Inline documentation for external scripts
      2. 4.3.2 The noscript element
    4. 4.4 Sections
      1. 4.4.1 The body element
      2. 4.4.2 The section element
      3. 4.4.3 The nav element
      4. 4.4.4 The article element
      5. 4.4.5 The aside element
      6. 4.4.6 The h1, h2, h3, h4, h5, and h6 elements
      7. 4.4.7 The hgroup element
      8. 4.4.8 The header element
      9. 4.4.9 The footer element
      10. 4.4.10 The address element
      11. 4.4.11 Headings and sections
        1. 4.4.11.1 Creating an outline
    5. 4.5 Grouping content
      1. 4.5.1 The p element
      2. 4.5.2 The hr element
      3. 4.5.3 The pre element
      4. 4.5.4 The blockquote element
      5. 4.5.5 The ol element
      6. 4.5.6 The ul element
      7. 4.5.7 The li element
      8. 4.5.8 The dl element
      9. 4.5.9 The dt element
      10. 4.5.10 The dd element
      11. 4.5.11 The figure element
      12. 4.5.12 The figcaption element
      13. 4.5.13 The div element
    6. 4.6 Text-level semantics
      1. 4.6.1 The a element
      2. 4.6.2 The em element
      3. 4.6.3 The strong element
      4. 4.6.4 The small element
      5. 4.6.5 The cite element
      6. 4.6.6 The q element
      7. 4.6.7 The dfn element
      8. 4.6.8 The abbr element
      9. 4.6.9 The time element
      10. 4.6.10 The code element
      11. 4.6.11 The var element
      12. 4.6.12 The samp element
      13. 4.6.13 The kbd element
      14. 4.6.14 The sub and sup elements
      15. 4.6.15 The i element
      16. 4.6.16 The b element
      17. 4.6.17 The mark element
      18. 4.6.18 The ruby element
      19. 4.6.19 The rt element
      20. 4.6.20 The rp element
      21. 4.6.21 The bdo element
      22. 4.6.22 The span element
      23. 4.6.23 The br element
      24. 4.6.24 The wbr element
      25. 4.6.25 Usage summary
    7. 4.7 Edits
      1. 4.7.1 The ins element
      2. 4.7.2 The del element
      3. 4.7.3 Attributes common to ins and del elements
      4. 4.7.4 Edits and paragraphs
      5. 4.7.5 Edits and lists
    8. 4.8 Embedded content
      1. 4.8.1 The img element
        1. 4.8.1.1 Requirements for providing text to act as an alternative for images
          1. 4.8.1.1.1 A link or button containing nothing but the image
          2. 4.8.1.1.2 A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations
          3. 4.8.1.1.3 A short phrase or label with an alternative graphical representation: icons, logos
          4. 4.8.1.1.4 Text that has been rendered to a graphic for typographical effect
          5. 4.8.1.1.5 A graphical representation of some of the surrounding text
          6. 4.8.1.1.6 A purely decorative image that doesn't add any information
          7. 4.8.1.1.7 A group of images that form a single larger picture with no links
          8. 4.8.1.1.8 A group of images that form a single larger picture with links
          9. 4.8.1.1.9 A key part of the content
          10. 4.8.1.1.10 An image not intended for the user
          11. 4.8.1.1.11 An image in an e-mail or private document intended for a specific person who is known to be able to view images
          12. 4.8.1.1.12 General guidelines
          13. 4.8.1.1.13 Guidance for markup generators
          14. 4.8.1.1.14 Guidance for conformance checkers
      2. 4.8.2 The iframe element
      3. 4.8.3 The embed element
      4. 4.8.4 The object element
      5. 4.8.5 The param element
      6. 4.8.6 The video element
      7. 4.8.7 The audio element
      8. 4.8.8 The source element
      9. 4.8.9 Media elements
        1. 4.8.9.1 Error codes
        2. 4.8.9.2 Location of the media resource
        3. 4.8.9.3 MIME types
        4. 4.8.9.4 Network states
        5. 4.8.9.5 Loading the media resource
        6. 4.8.9.6 Offsets into the media resource
        7. 4.8.9.7 The ready states
        8. 4.8.9.8 Playing the media resource
        9. 4.8.9.9 Seeking
        10. 4.8.9.10 User interface
        11. 4.8.9.11 Time ranges
        12. 4.8.9.12 Event summary
        13. 4.8.9.13 Security and privacy considerations
      10. 4.8.10 The canvas element
        1. 4.8.10.1 Color spaces and color correction
        2. 4.8.10.2 Security with canvas elements
      11. 4.8.11 The map element
      12. 4.8.12 The area element
      13. 4.8.13 Image maps
        1. 4.8.13.1 Authoring
        2. 4.8.13.2 Processing model
      14. 4.8.14 MathML
      15. 4.8.15 SVG
      16. 4.8.16 Dimension attributes
    9. 4.9 Tabular data
      1. 4.9.1 The table element
      2. 4.9.2 The caption element
      3. 4.9.3 The colgroup element
      4. 4.9.4 The col element
      5. 4.9.5 The tbody element
      6. 4.9.6 The thead element
      7. 4.9.7 The tfoot element
      8. 4.9.8 The tr element
      9. 4.9.9 The td element
      10. 4.9.10 The th element
      11. 4.9.11 Attributes common to td and th elements
      12. 4.9.12 Processing model
        1. 4.9.12.1 Forming a table
        2. 4.9.12.2 Forming relationships between data cells and header cells
      13. 4.9.13 Examples
    10. 4.10 Forms
      1. 4.10.1 Introduction
        1. 4.10.1.1 Writing a form's user interface
        2. 4.10.1.2 Implementing the server-side processing for a form
        3. 4.10.1.3 Configuring a form to communicate with a server
        4. 4.10.1.4 Client-side form validation
      2. 4.10.2 Categories
      3. 4.10.3 The form element
      4. 4.10.4 The fieldset element
      5. 4.10.5 The legend element
      6. 4.10.6 The label element
      7. 4.10.7 The input element
        1. 4.10.7.1 States of the type attribute
          1. 4.10.7.1.1 Hidden state
          2. 4.10.7.1.2 Text state and Search state
          3. 4.10.7.1.3 Telephone state
          4. 4.10.7.1.4 URL state
          5. 4.10.7.1.5 E-mail state
          6. 4.10.7.1.6 Password state
          7. 4.10.7.1.7 Date and Time state
          8. 4.10.7.1.8 Date state
          9. 4.10.7.1.9 Month state
          10. 4.10.7.1.10 Week state
          11. 4.10.7.1.11 Time state
          12. 4.10.7.1.12 Local Date and Time state
          13. 4.10.7.1.13 Number state
          14. 4.10.7.1.14 Range state
          15. 4.10.7.1.15 Color state
          16. 4.10.7.1.16 Checkbox state
          17. 4.10.7.1.17 Radio Button state
          18. 4.10.7.1.18 File Upload state
          19. 4.10.7.1.19 Submit Button state
          20. 4.10.7.1.20 Image Button state
          21. 4.10.7.1.21 Reset Button state
          22. 4.10.7.1.22 Button state
        2. 4.10.7.2 Common input element attributes
          1. 4.10.7.2.1 The autocomplete attribute
          2. 4.10.7.2.2 The list attribute
          3. 4.10.7.2.3 The readonly attribute
          4. 4.10.7.2.4 The size attribute
          5. 4.10.7.2.5 The required attribute
          6. 4.10.7.2.6 The multiple attribute
          7. 4.10.7.2.7 The maxlength attribute
          8. 4.10.7.2.8 The pattern attribute
          9. 4.10.7.2.9 The min and max attributes
          10. 4.10.7.2.10 The step attribute
          11. 4.10.7.2.11 The placeholder attribute
        3. 4.10.7.3 Common input element APIs
        4. 4.10.7.4 Common event behaviors
      8. 4.10.8 The button element
      9. 4.10.9 The select element
      10. 4.10.10 The datalist element
      11. 4.10.11 The optgroup element
      12. 4.10.12 The option element
      13. 4.10.13 The textarea element
      14. 4.10.14 The keygen element
      15. 4.10.15 The output element
      16. 4.10.16 The progress element
      17. 4.10.17 The meter element
      18. 4.10.18 Association of controls and forms
      19. 4.10.19 Attributes common to form controls
        1. 4.10.19.1 Naming form controls
        2. 4.10.19.2 Enabling and disabling form controls
        3. 4.10.19.3 A form control's value
        4. 4.10.19.4 Autofocusing a form control
        5. 4.10.19.5 Limiting user input length
        6. 4.10.19.6 Form submission
      20. 4.10.20 Constraints
        1. 4.10.20.1 Definitions
        2. 4.10.20.2 Constraint validation
        3. 4.10.20.3 The constraint validation API
        4. 4.10.20.4 Security
      21. 4.10.21 Form submission
        1. 4.10.21.1 Introduction
        2. 4.10.21.2 Implicit submission
        3. 4.10.21.3 Form submission algorithm
        4. 4.10.21.4 URL-encoded form data
        5. 4.10.21.5 Multipart form data
        6. 4.10.21.6 Plain text form data
      22. 4.10.22 Resetting a form
      23. 4.10.23 Event dispatch
    11. 4.11 Interactive elements
      1. 4.11.1 The details element
      2. 4.11.2 The summary element
      3. 4.11.3 The command element
      4. 4.11.4 The menu element
        1. 4.11.4.1 Introduction
        2. 4.11.4.2 Building menus and toolbars
        3. 4.11.4.3 Context menus
        4. 4.11.4.4 Toolbars
      5. 4.11.5 Commands
        1. 4.11.5.1 Using the a element to define a command
        2. 4.11.5.2 Using the button element to define a command
        3. 4.11.5.3 Using the input element to define a command
        4. 4.11.5.4 Using the option element to define a command
        5. 4.11.5.5 Using the command element to define a command
        6. 4.11.5.6 Using the accesskey attribute on a label element to define a command
        7. 4.11.5.7 Using the accesskey attribute on a legend element to define a command
        8. 4.11.5.8 Using the accesskey attribute to define a command on other elements
    12. 4.12 Links
      1. 4.12.1 Hyperlink elements
      2. 4.12.2 Following hyperlinks
      3. 4.12.3 Link types
        1. 4.12.3.1 Link type "alternate"
        2. 4.12.3.2 Link type "archives"
        3. 4.12.3.3 Link type "author"
        4. 4.12.3.4 Link type "bookmark"
        5. 4.12.3.5 Link type "external"
        6. 4.12.3.6 Link type "help"
        7. 4.12.3.7 Link type "icon"
        8. 4.12.3.8 Link type "license"
        9. 4.12.3.9 Link type "nofollow"
        10. 4.12.3.10 Link type "noreferrer"
        11. 4.12.3.11 Link type "pingback"
        12. 4.12.3.12 Link type "prefetch"
        13. 4.12.3.13 Link type "search"
        14. 4.12.3.14 Link type "stylesheet"
        15. 4.12.3.15 Link type "sidebar"
        16. 4.12.3.16 Link type "tag"
        17. 4.12.3.17 Hierarchical link types
          1. 4.12.3.17.1 Link type "index"
          2. 4.12.3.17.2 Link type "up"
        18. 4.12.3.18 Sequential link types
          1. 4.12.3.18.1 Link type "first"
          2. 4.12.3.18.2 Link type "last"
          3. 4.12.3.18.3 Link type "next"
          4. 4.12.3.18.4 Link type "prev"
        19. 4.12.3.19 Other link types
    13. 4.13 Common idioms without dedicated elements
      1. 4.13.1 Tag clouds
      2. 4.13.2 Conversations
      3. 4.13.3 Footnotes
    14. 4.14 Matching HTML elements using selectors
      1. 4.14.1 Case-sensitivity
      2. 4.14.2 Pseudo-classes
  5. 5 Loading Web pages
    1. 5.1 Browsing contexts
      1. 5.1.1 Nested browsing contexts
        1. 5.1.1.1 Navigating nested browsing contexts in the DOM
      2. 5.1.2 Auxiliary browsing contexts
        1. 5.1.2.1 Navigating auxiliary browsing contexts in the DOM
      3. 5.1.3 Secondary browsing contexts
      4. 5.1.4 Security
      5. 5.1.5 Groupings of browsing contexts
      6. 5.1.6 Browsing context names
    2. 5.2 The Window object
      1. 5.2.1 Security
      2. 5.2.2 APIs for creating and navigating browsing contexts by name
      3. 5.2.3 Accessing other browsing contexts
      4. 5.2.4 Named access on the Window object
      5. 5.2.5 Garbage collection and browsing contexts
      6. 5.2.6 Browser interface elements
      7. 5.2.7 The WindowProxy object
    3. 5.3 Origin
      1. 5.3.1 Relaxing the same-origin restriction
    4. 5.4 Session history and navigation
      1. 5.4.1 The session history of browsing contexts
      2. 5.4.2 The History interface
      3. 5.4.3 The Location interface
        1. 5.4.3.1 Security
      4. 5.4.4 Implementation notes for session history
    5. 5.5 Browsing the Web
      1. 5.5.1 Navigating across documents
      2. 5.5.2 Page load processing model for HTML files
      3. 5.5.3 Page load processing model for XML files
      4. 5.5.4 Page load processing model for text files
      5. 5.5.5 Page load processing model for images
      6. 5.5.6 Page load processing model for content that uses plugins
      7. 5.5.7 Page load processing model for inline content that doesn't have a DOM
      8. 5.5.8 Navigating to a fragment identifier
      9. 5.5.9 History traversal
        1. 5.5.9.1 Event definitions
      10. 5.5.10 Unloading documents
        1. 5.5.10.1 Event definition
      11. 5.5.11 Aborting a document load
    6. 5.6 Offline Web applications
      1. 5.6.1 Introduction
        1. 5.6.1.1 Event summary
      2. 5.6.2 Application caches
      3. 5.6.3 The cache manifest syntax
        1. 5.6.3.1 A sample manifest
        2. 5.6.3.2 Writing cache manifests
        3. 5.6.3.3 Parsing cache manifests
      4. 5.6.4 Downloading or updating an application cache
      5. 5.6.5 The application cache selection algorithm
      6. 5.6.6 Changes to the networking model
      7. 5.6.7 Expiring application caches
      8. 5.6.8 Application cache API
      9. 5.6.9 Browser state
  6. 6 Web application APIs
    1. 6.1 Scripting
      1. 6.1.1 Introduction
      2. 6.1.2 Enabling and disabling scripting
      3. 6.1.3 Processing model
        1. 6.1.3.1 Definitions
        2. 6.1.3.2 Calling scripts
        3. 6.1.3.3 Creating scripts
        4. 6.1.3.4 Killing scripts
      4. 6.1.4 Event loops
        1. 6.1.4.1 Definitions
        2. 6.1.4.2 Processing model
        3. 6.1.4.3 Generic task sources
      5. 6.1.5 The javascript: protocol
      6. 6.1.6 Events
        1. 6.1.6.1 Event handlers
        2. 6.1.6.2 Event handlers on elements, Document objects, and Window objects
        3. 6.1.6.3 Event firing
        4. 6.1.6.4 Events and the Window object
        5. 6.1.6.5 Runtime script errors
    2. 6.2 Timers
    3. 6.3 User prompts
      1. 6.3.1 Simple dialogs
      2. 6.3.2 Printing
      3. 6.3.3 Dialogs implemented using separate documents
    4. 6.4 System state and capabilities
      1. 6.4.1 Client identification
      2. 6.4.2 Custom scheme and content handlers
        1. 6.4.2.1 Security and privacy
        2. 6.4.2.2 Sample user interface
      3. 6.4.3 Manually releasing the storage mutex
  7. 7 User interaction
    1. 7.1 The hidden attribute
    2. 7.2 Activation
    3. 7.3 Scrolling elements into view
    4. 7.4 Focus
      1. 7.4.1 Sequential focus navigation
      2. 7.4.2 Focus management
      3. 7.4.3 Document-level focus APIs
      4. 7.4.4 Element-level focus APIs
    5. 7.5 The accesskey attribute
    6. 7.6 The text selection APIs
      1. 7.6.1 APIs for the browsing context selection
      2. 7.6.2 APIs for the text field selections
    7. 7.7 The contenteditable attribute
      1. 7.7.1 User editing actions
      2. 7.7.2 Making entire documents editable
    8. 7.8 Spelling and grammar checking
    9. 7.9 Drag and drop
      1. 7.9.1 Introduction
      2. 7.9.2 The DragEvent and DataTransfer interfaces
      3. 7.9.3 Events fired during a drag-and-drop action
      4. 7.9.4 Drag-and-drop processing model
        1. 7.9.4.1 When the drag-and-drop operation starts or ends in another document
        2. 7.9.4.2 When the drag-and-drop operation starts or ends in another application
      5. 7.9.5 The draggable attribute
      6. 7.9.6 Security risks in the drag-and-drop model
    10. 7.10 Undo history
      1. 7.10.1 Definitions
      2. 7.10.2 The UndoManager interface
      3. 7.10.3 Undo: moving back in the undo transaction history
      4. 7.10.4 Redo: moving forward in the undo transaction history
      5. 7.10.5 The UndoManagerEvent interface and the undo and redo events
      6. 7.10.6 Implementation notes
    11. 7.11 Editing APIs
  8. 8 The HTML syntax
    1. 8.1 Writing HTML documents
      1. 8.1.1 The DOCTYPE
      2. 8.1.2 Elements
        1. 8.1.2.1 Start tags
        2. 8.1.2.2 End tags
        3. 8.1.2.3 Attributes
        4. 8.1.2.4 Optional tags
        5. 8.1.2.5 Restrictions on content models
        6. 8.1.2.6 Restrictions on the contents of raw text and RCDATA elements
      3. 8.1.3 Text
        1. 8.1.3.1 Newlines
      4. 8.1.4 Character references
      5. 8.1.5 CDATA sections
      6. 8.1.6 Comments
    2. 8.2 Parsing HTML documents
      1. 8.2.1 Overview of the parsing model
      2. 8.2.2 The input stream
        1. 8.2.2.1 Determining the character encoding
        2. 8.2.2.2 Character encodings
        3. 8.2.2.3 Preprocessing the input stream
        4. 8.2.2.4 Changing the encoding while parsing
      3. 8.2.3 Parse state
        1. 8.2.3.1 The insertion mode
        2. 8.2.3.2 The stack of open elements
        3. 8.2.3.3 The list of active formatting elements
        4. 8.2.3.4 The element pointers
        5. 8.2.3.5 Other parsing state flags
      4. 8.2.4 Tokenization
        1. 8.2.4.1 Data state
        2. 8.2.4.2 Character reference in data state
        3. 8.2.4.3 RCDATA state
        4. 8.2.4.4 Character reference in RCDATA state
        5. 8.2.4.5 RAWTEXT state
        6. 8.2.4.6 Script data state
        7. 8.2.4.7 PLAINTEXT state
        8. 8.2.4.8 Tag open state
        9. 8.2.4.9 End tag open state
        10. 8.2.4.10 Tag name state
        11. 8.2.4.11 RCDATA less-than sign state
        12. 8.2.4.12 RCDATA end tag open state
        13. 8.2.4.13 RCDATA end tag name state
        14. 8.2.4.14 RAWTEXT less-than sign state
        15. 8.2.4.15 RAWTEXT end tag open state
        16. 8.2.4.16 RAWTEXT end tag name state
        17. 8.2.4.17 Script data less-than sign state
        18. 8.2.4.18 Script data end tag open state
        19. 8.2.4.19 Script data end tag name state
        20. 8.2.4.20 Script data escape start state
        21. 8.2.4.21 Script data escape start dash state
        22. 8.2.4.22 Script data escaped state
        23. 8.2.4.23 Script data escaped dash state
        24. 8.2.4.24 Script data escaped dash dash state
        25. 8.2.4.25 Script data escaped less-than sign state
        26. 8.2.4.26 Script data escaped end tag open state
        27. 8.2.4.27 Script data escaped end tag name state
        28. 8.2.4.28 Script data double escape start state
        29. 8.2.4.29 Script data double escaped state
        30. 8.2.4.30 Script data double escaped dash state
        31. 8.2.4.31 Script data double escaped dash dash state
        32. 8.2.4.32 Script data double escaped less-than sign state
        33. 8.2.4.33 Script data double escape end state
        34. 8.2.4.34 Before attribute name state
        35. 8.2.4.35 Attribute name state
        36. 8.2.4.36 After attribute name state
        37. 8.2.4.37 Before attribute value state
        38. 8.2.4.38 Attribute value (double-quoted) state
        39. 8.2.4.39 Attribute value (single-quoted) state
        40. 8.2.4.40 Attribute value (unquoted) state
        41. 8.2.4.41 Character reference in attribute value state
        42. 8.2.4.42 After attribute value (quoted) state
        43. 8.2.4.43 Self-closing start tag state
        44. 8.2.4.44 Bogus comment state
        45. 8.2.4.45 Markup declaration open state
        46. 8.2.4.46 Comment start state
        47. 8.2.4.47 Comment start dash state
        48. 8.2.4.48 Comment state
        49. 8.2.4.49 Comment end dash state
        50. 8.2.4.50 Comment end state
        51. 8.2.4.51 Comment end bang state
        52. 8.2.4.52 Comment end space state
        53. 8.2.4.53 DOCTYPE state
        54. 8.2.4.54 Before DOCTYPE name state
        55. 8.2.4.55 DOCTYPE name state
        56. 8.2.4.56 After DOCTYPE name state
        57. 8.2.4.57 After DOCTYPE public keyword state
        58. 8.2.4.58 Before DOCTYPE public identifier state
        59. 8.2.4.59 DOCTYPE public identifier (double-quoted) state
        60. 8.2.4.60 DOCTYPE public identifier (single-quoted) state
        61. 8.2.4.61 After DOCTYPE public identifier state
        62. 8.2.4.62 Between DOCTYPE public and system identifiers state
        63. 8.2.4.63 After DOCTYPE system keyword state
        64. 8.2.4.64 Before DOCTYPE system identifier state
        65. 8.2.4.65 DOCTYPE system identifier (double-quoted) state
        66. 8.2.4.66 DOCTYPE system identifier (single-quoted) state
        67. 8.2.4.67 After DOCTYPE system identifier state
        68. 8.2.4.68 Bogus DOCTYPE state
        69. 8.2.4.69 CDATA section state
        70. 8.2.4.70 Tokenizing character references
      5. 8.2.5 Tree construction
        1. 8.2.5.1 Creating and inserting elements
        2. 8.2.5.2 Closing elements that have implied end tags
        3. 8.2.5.3 Foster parenting
        4. 8.2.5.4 The "initial" insertion mode
        5. 8.2.5.5 The "before html" insertion mode
        6. 8.2.5.6 The "before head" insertion mode
        7. 8.2.5.7 The "in head" insertion mode
        8. 8.2.5.8 The "in head noscript" insertion mode
        9. 8.2.5.9 The "after head" insertion mode
        10. 8.2.5.10 The "in body" insertion mode
        11. 8.2.5.11 The "text" insertion mode
        12. 8.2.5.12 The "in table" insertion mode
        13. 8.2.5.13 The "in table text" insertion mode
        14. 8.2.5.14 The "in caption" insertion mode
        15. 8.2.5.15 The "in column group" insertion mode
        16. 8.2.5.16 The "in table body" insertion mode
        17. 8.2.5.17 The "in row" insertion mode
        18. 8.2.5.18 The "in cell" insertion mode
        19. 8.2.5.19 The "in select" insertion mode
        20. 8.2.5.20 The "in select in table" insertion mode
        21. 8.2.5.21 The "in foreign content" insertion mode
        22. 8.2.5.22 The "after body" insertion mode
        23. 8.2.5.23 The "in frameset" insertion mode
        24. 8.2.5.24 The "after frameset" insertion mode
        25. 8.2.5.25 The "after after body" insertion mode
        26. 8.2.5.26 The "after after frameset" insertion mode
      6. 8.2.6 The end
      7. 8.2.7 Coercing an HTML DOM into an infoset
      8. 8.2.8 An introduction to error handling and strange cases in the parser
        1. 8.2.8.1 Misnested tags: <b><i></b></i>
        2. 8.2.8.2 Misnested tags: <b><p></b></p>
        3. 8.2.8.3 Unexpected markup in tables
        4. 8.2.8.4 Scripts that modify the page as it is being parsed
    3. 8.3 Serializing HTML fragments
    4. 8.4 Parsing HTML fragments
    5. 8.5 Named character references
  9. 9 The XHTML syntax
    1. 9.1 Writing XHTML documents
    2. 9.2 Parsing XHTML documents
    3. 9.3 Serializing XHTML fragments
    4. 9.4 Parsing XHTML fragments
  10. 10 Rendering
    1. 10.1 Introduction
    2. 10.2 The CSS user agent style sheet and presentational hints
      1. 10.2.1 Introduction
      2. 10.2.2 Display types
      3. 10.2.3 Margins and padding
      4. 10.2.4 Alignment
      5. 10.2.5 Fonts and colors
      6. 10.2.6 Punctuation and decorations
      7. 10.2.7 Resetting rules for inherited properties
      8. 10.2.8 The hr element
      9. 10.2.9 The fieldset element
    3. 10.3 Replaced elements
      1. 10.3.1 Embedded content
      2. 10.3.2 Images
      3. 10.3.3 Attributes for embedded content and images
      4. 10.3.4 Image maps
      5. 10.3.5 Toolbars
    4. 10.4 Bindings
      1. 10.4.1 Introduction
      2. 10.4.2 The button element
      3. 10.4.3 The details element
      4. 10.4.4 The input element as a text entry widget
      5. 10.4.5 The input element as domain-specific widgets
      6. 10.4.6 The input element as a range control
      7. 10.4.7 The input element as a color well
      8. 10.4.8 The input element as a check box and radio button widgets
      9. 10.4.9 The input element as a file upload control
      10. 10.4.10 The input element as a button
      11. 10.4.11 The marquee element
      12. 10.4.12 The meter element
      13. 10.4.13 The progress element
      14. 10.4.14 The select element
      15. 10.4.15 The textarea element
      16. 10.4.16 The keygen element
      17. 10.4.17 The time element
    5. 10.5 Frames and framesets
    6. 10.6 Interactive media
      1. 10.6.1 Links, forms, and navigation
      2. 10.6.2 The title attribute
      3. 10.6.3 Editing hosts
    7. 10.7 Print media
  11. 11 Obsolete features
    1. 11.1 Obsolete but conforming features
      1. 11.1.1 Warnings for obsolete but conforming features
    2. 11.2 Non-conforming features
    3. 11.3 Requirements for implementations
      1. 11.3.1 The applet element
      2. 11.3.2 The marquee element
      3. 11.3.3 Frames
      4. 11.3.4 Other elements, attributes and APIs
  12. 12 IANA considerations
    1. 12.1 text/html
    2. 12.2 text/html-sandboxed
    3. 12.3 application/xhtml+xml
    4. 12.4 text/cache-manifest
  13. Index
    1. Elements
    2. Element content categories
    3. Attributes
    4. Interfaces
    5. Events
  14. References
  15. Acknowledgements

1 Introduction

Status: Last call for comments

1.1 Background

Status: Last call for comments

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 have enabled it to be used to describe a number of other types of documents.

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

1.2 Audience

Status: Last call for comments

This section is non-normative.

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

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

In particular, familiarity with the basics of DOM Core and DOM Events is necessary for a complete understanding of some of the more technical parts of this specification. An understanding of Web IDL, HTTP, XML, Unicode, character encodings, JavaScript, and CSS will also be helpful in places but is not essential.

1.3 Scope

Status: Last call for comments

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

1.4 History

Status: Last call for comments

This section is non-normative.

For its first five years (1990-1995), HTML went through a number of revisions and experienced a number of extensions, primarily hosted first at CERN, and then at the IETF.

With the creation of the W3C, HTML's development changed venue again. A first abortive attempt at extending HTML in 1995 known as HTML 3.0 then made way to a more pragmatic approach known as HTML 3.2, which was completed in 1997. HTML4 followed, reaching completion in 1998.

At this time, the W3C membership decided to stop evolving HTML and instead begin work on an XML-based equivalent, called XHTML. This effort started with a reformulation of HTML4 in XML, known as XHTML 1.0, which added no new features except the new serialization, and which was completed in 2000. After XHTML 1.0, the W3C's focus turned to making it easier for other working groups to extend XHTML, under the banner of XHTML Modularization. In parallel with this, the W3C also worked on a new language that was not compatible with the earlier HTML and XHTML languages, calling it XHTML2.

Around the time that HTML's evolution was stopped in 1998, parts of the API for HTML developed by browser vendors were specified and published under the name DOM Level 1 (in 1998) and DOM Level 2 Core and DOM Level 2 HTML (starting in 2000 and culminating in 2003). These efforts then petered out, with some DOM Level 3 specifications published in 2004 but the working group being closed before all the Level 3 drafts were completed.

In 2003, the publication of XForms, a technology which was positioned as the next generation of Web forms, sparked a renewed interest in evolving HTML itself, rather than finding replacements for it. This interest was borne from the realization that XML's deployment as a Web technology was limited to entirely new technologies (like RSS and later Atom), rather than as a replacement for existing deployed technologies (like HTML).

A proof of concept to show that it was possible to extend HTML4's forms to provide many of the features that XForms 1.0 introduced, without requiring browsers to implement rendering engines that were incompatible with existing HTML Web pages, was the first result of this renewed interest. At this early stage, while the draft was already publicly available, and input was already being solicited from all sources, the specification was only under Opera Software's copyright.

The idea that HTML's evolution should be reopened was tested at a W3C workshop in 2004, where some of the principles that underlie the HTML5 work (described below), as well as the aforementioned early draft proposal covering just forms-related features, were presented to the W3C jointly by Mozilla and Opera. The proposal was rejected on the grounds that the proposal conflicted with the previously chosen direction for the Web's evolution; the W3C staff and membership voted to continue developing XML-based replacements instead.

Shortly thereafter, Apple, Mozilla, and Opera jointly announced their intent to continue working on the effort under the umbrella of a new venue called the WHATWG. A public mailing list was created, and the draft was moved to the WHATWG site. The copyright was subsequently amended to be jointly owned by all three vendors, and to allow reuse of the specification.

The WHATWG was based on several core principles, in particular that technologies need to be backwards compatible, that specifications and implementations need to match even if this means changing the specification rather than the implementations, and that specifications need to be detailed enough that implementations can achieve complete interoperability without reverse-engineering each other.

The latter requirement in particular required that the scope of the HTML5 specification include what had previously been specified in three separate documents: HTML4, XHTML1, and DOM2 HTML. It also meant including significantly more detail than had previously been considered the norm.

In 2006, the W3C indicated an interest to participate in the development of HTML5 after all, and in 2007 formed a working group chartered to work with the WHATWG on the development of the HTML5 specification. Apple, Mozilla, and Opera allowed the W3C to publish the specification under the W3C copyright, while keeping a version with the less restrictive license on the WHATWG site.

Since then, both groups have been working together.

The HTML specification published by the WHATWG is not identical to this specification. At the time of this publication, the main differences were that the WHATWG version included features not included in this W3C version: some features have been omitted, but may be considered for future revisions of HTML beyond HTML5; and other features were omitted because at the W3C they are published as separate specifications.

A separate document has been published by the W3C HTML working group to document the differences between this specification and the language described in the HTML4 specification. [HTMLDIFF]

1.5 Design notes

Status: Last call for comments

This section is non-normative.

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

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

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

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

1.5.1 Serializability of script execution

Status: Last call for comments

This section is non-normative.

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

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

1.5.2 Compliance with other specifications

Status: Last call for comments

This section is non-normative.

This specification interacts with and relies on a wide variety of other specifications. In certain circumstances, unfortunately, conflicting needs have led to this specification violating the requirements of these other specifications. Whenever this has occurred, the transgressions have each been noted as a "willful violation", and the reason for the violation has been noted.

1.6 HTML vs XHTML

Status: Last call for comments

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 "DOM HTML", or "the DOM" for short. This specification defines version 5 of DOM HTML, known as "DOM5 HTML".

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 the HTML syntax. This is the format suggested for most authors. It is compatible with most legacy Web browsers. If a document is transmitted with an HTML MIME type, such as text/html, then it will be processed as an HTML document by Web browsers. This specification defines version 5 of the HTML syntax, known as "HTML5".

The second concrete syntax is the XHTML syntax, which is an application of XML. When a document is transmitted with an XML MIME type, such as application/xhtml+xml, then it is treated as an XML document by Web browsers, to be parsed by an XML processor. Authors are reminded that the processing for XML and HTML differs; in particular, even minor syntax errors will prevent a document labeled as XML from being rendered fully, whereas they would be ignored in the HTML syntax. This specification defines version 5 of the XHTML syntax, known as "XHTML5".

The DOM, the HTML syntax, and XML cannot all represent the same content. For example, namespaces cannot be represented using the HTML syntax, but they are supported in the DOM and in XML. Similarly, documents that use the noscript feature can be represented using the HTML syntax, but cannot be represented with the DOM or in XML. Comments that contain the string "-->" can be represented in the DOM but not in the HTML syntax or in XML.

1.7 Structure of this specification

Status: Last call for comments

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.
Semantics, structure, and APIs of HTML documents
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.
The elements of HTML
Each element has a predefined meaning, which is explained in this section. Rules for authors on how to use the element, along with user agent requirements for how to handle each element, are also given.
Loading Web pages
HTML documents do not exist in a vacuum — this section defines many of the features that affect environments that deal with multiple pages.
Web application APIs
This section introduces basic features for scripting of applications in HTML.
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 HTML syntax
The XHTML 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 these sections define the syntaxes of HTML, along with rules for how to parse content using those syntaxes.

There are also some appendices, defining rendering rules for Web browsers and listing obsolete features and IANA considerations.

1.7.1 How to read this specification

Status: Last call for comments

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

1.7.2 Typographic conventions

Status: Last call for comments

This is a definition, requirement, or explanation.

This is a note.

This is an example.

This is an open issue.

This is a warning.

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

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

/* this is a CSS fragment */

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

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

Other code fragments are marked up like this.

Variables are marked up like this.

This is an implementation requirement.

1.8 A quick introduction to HTML

Status: Last call for comments

This section is non-normative.

A basic HTML document looks like this:

<!DOCTYPE html>
<html>
 <head>
  <title>Sample page</title>
 </head>
 <body>
  <h1>Sample page</h1>
  <p>This is a <a href="demo.html">simple</a> sample.</p>
  <!-- this is a comment -->
 </body>
</html>

HTML documents consist of a tree of elements and text. Each element is denoted in the source by a start tag, such as "<body>", and an end tag, such as "</body>". (Certain start tags and end tags can in certain cases be omitted and are implied by other tags.)

Tags have to be nested such that elements are all completely within each other, without overlapping:

<p>This is <em>very <strong>wrong</em>!</strong></p>
<p>This <em>is <strong>correct</strong>.</em></p>

This specification defines a set of elements that can be used in HTML, along with rules about the ways in which the elements can be nested.

Elements can have attributes, which control how the elements work. In the example below, there is a hyperlink, formed using the a element and its href attribute:

<a href="demo.html">simple</a>

Attributes are placed inside the start tag, and consist of a name and a value, separated by an "=" character. The attribute value can remain unquoted if it doesn't contain spaces or any of " ' ` = < or >. Otherwise, it has to be quoted using either single or double quotes. The value, along with the "=" character, can be omitted altogether if the value is the empty string.

<!-- empty attributes -->
<input name=address disabled>
<input name=address disabled="">

<!-- attributes with a value -->
<input name=address maxlength=200>
<input name=address maxlength='200'>
<input name=address maxlength="200">

HTML user agents (e.g. Web browsers) then parse this markup, turning it into a DOM (Document Object Model) tree. A DOM tree is an in-memory representation of a document.

DOM trees contain several kinds of nodes, in particular a DOCTYPE node, elements, text nodes, and comment nodes.

The markup snippet at the top of this section would be turned into the following DOM tree:

The root element of this tree is the html element, which is the element always found at the root of HTML documents. It contains two elements, head and body, as well as a text node between them.

There are many more text nodes in the DOM tree than one would initially expect, because the source contains a number of spaces (represented here by "␣") and line breaks ("⏎") that all end up as text nodes in the DOM.

The head element contains a title element, which itself contains a text node with the text "Sample page". Similarly, the body element contains an h1 element, a p element, and a comment.


This DOM tree can be manipulated from scripts in the page. Scripts (typically in JavaScript) are small programs that can be embedded using the script element or using event handler content attributes. For example, here is a form with a script that sets the value of the form's output element to say "Hello World":

<form name="main">
 Result: <output name="result"></output>
 <script>
  document.forms.main.elements.result.value = 'Hello World';
 </script>
</form>

Each element in the DOM tree is represented by an object, and these objects have APIs so that they can be manipulated. For instance, a link (e.g. the a element in the tree above) can have its "href" attribute changed in several ways:

var a = document.links[0]; // obtain the first link in the document
a.href = 'sample.html'; // change the destination URL of the link
a.protocol = 'https'; // change just the scheme part of the URL
a.setAttribute('href', 'http://example.com/'); // change the content attribute directly

Since DOM trees are used as the way to represent HTML documents when they are processed and presented by implementations (especially interactive implementations like Web browsers), this specification is mostly phrased in terms of DOM trees, instead of the markup described above.


HTML documents represent a media-independent description of interactive content. HTML documents might be rendered to a screen, or through a speech synthesizer, or on a braille display. To influence exactly how such rendering takes place, authors can use a styling language such as CSS.

In the following example, the page has been made yellow-on-blue using CSS.

<!DOCTYPE html>
<html>
 <head>
  <title>Sample styled page</title>
  <style>
   body { background: navy; color: yellow; }
  </style>
 </head>
 <body>
  <h1>Sample styled page</h1>
  <p>This page is just a demo.</p>
 </body>
</html>

For more details on how to use HTML, authors are encouraged to consult tutorials and guides. Some of the examples included in this specification might also be of use, but the novice author is cautioned that this specification, by necessity, defines the language with a level of detail that might be difficult to understand at first.

1.9 Conformance requirements for authors

This section is non-normative.

Unlike previous versions of the HTML specification, this specification defines in some detail the required processing for invalid documents as well as valid documents.

However, even though the processing of invalid content is in most cases well-defined, conformance requirements for documents are still important: in practice, interoperability (the situation in which all implementations process particular content in a reliable and identical or equivalent way) is not the only goal of document conformance requirements. This section details some of the more common reasons for still distinguishing between a conforming document and one with errors.

1.9.1 Presentational markup

This section is non-normative.

The majority of presentational features from previous versions of HTML are no longer allowed. Presentational markup in general has been found to have a number of problems:

The use of presentational elements leads to poorer accessibility

While it is possible to use presentational markup in a way that provides users of assistive technologies (ATs) with an acceptable experience (e.g. using ARIA), doing so is significantly more difficult than doing so when using semantically-appropriate markup. Furthermore, even using such techniques doesn't help make pages accessible for non-AT non-graphical users, such as users of text-mode browsers.

Using media-independent markup, on the other hand, provides an easy way for documents to be authored in such a way that they work for more users (e.g. text browsers).

Higher cost of maintenance

It is significantly easier to maintain a site written in such a way that the markup is style-independent. For example, changing the color of a site that uses <font color=""> throughout requires changes across the entire site, whereas a similar change to a site based on CSS can be done by changing a single file.

Higher document sizes

Presentational markup tends to be much more redundant, and thus results in larger document sizes.

For those reasons, presentational markup has been removed from HTML in this version. This change should not come as a surprise; HTML4 deprecated presentational markup many years ago and provided a mode (HTML4 Transitional) to help authors move away from presentational markup; later, XHTML 1.1 went further and obsoleted those features altogether.

The only remaining presentational markup features in HTML are the style attribute and the style element. Use of the style attribute is somewhat discouraged in production environments, but it can be useful for rapid prototyping (where its rules can be directly moved into a separate style sheet later) and for providing specific styles in unusual cases where a separate style sheet would be inconvenient. Similarly, the style element can be useful in syndication or for page-specific styles, but in general an external style sheet is likely to be more convenient when the styles apply to multiple pages.

It is also worth noting that four elements that were previously presentational have been redefined in this specification to be media-independent: b, i, hr, and small.

1.9.2 Syntax errors

This section is non-normative.

The syntax of HTML is constrained to avoid a wide variety of problems.

Unintuitive error-handling behavior

Certain invalid syntax constructs, when parsed, result in DOM trees that are highly unintuitive.

For example, the following markup fragment results in a DOM with an hr element that is an earlier sibling of the corresponding table element:

<table><hr>...
Errors with optional error recovery

To allow user agents to be used in controlled environments without having to implement the more bizarre and convoluted error handling rules, user agents are permitted to fail whenever encountering a parse error.

Errors where the error-handling behavior is not compatible with streaming user agents

Some error-handling behavior, such as the behavior for the <table><hr>... example mentioned above, are incompatible with streaming user agents. To avoid interoperability problems with such user agents, any syntax resulting in such behavior is considered invalid.

Errors that can result in infoset coercion

When a user agent based on XML is connected to an HTML parser, it is possible that certain invariants that XML enforces, such as comments never containing two consecutive hyphens, will be violated by an HTML file. Handling this can require that the parser coerce the HTML DOM into an XML-compatible infoset. Most syntax constructs that require such handling are considered invalid.

Errors that result in disproportionally poor performance

Certain syntax constructs can result in disproportionally poor performance. To discourage the use of such constructs, they are typically made non-conforming.

For example, the following markup results in poor performance when hitting the highlighted end tag, since all the open elements are examined first to see if they match the close tag:

<p><em><span><span><span>...<span><span><span></em>
Errors involving fragile syntax constructs

There are syntax constructs that, for historical reasons, are relatively fragile. To help reduce the number of users who accidentally run into such problems, they are made non-conforming.

For example, the parsing of certain named character references in attributes happens even with the closing semicolon being omitted. It is safe to include an ampersand followed by letters that do not form a named character reference, but if the letters are changed to a string that does form a named character reference, they will be interpreted as that character instead.

In this fragment, the attribute's value is "?hello=1&world=2":

<a href="?hello=1&world=2">Demo</a>

In the following fragment, however, the attribute's value is actually "?original=1©=2", not the intended "?original=1&copy=2":

<a href="?original=1&copy=2">Compare</a>

To avoid this problem, all named character references are required to end with a semicolon, and uses of named character references without a semicolon are flagged as errors.

Thus, the correct way to express the above cases is as follows:

<a href="?hello=1&world=2">Demo</a> <!-- &world is ok, since it's not a named character reference -->
<a href="?original=1&amp;copy=2">Compare</a> <!-- the & has to be escaped, since &copy is a named character reference -->
Errors involving known interoperability problems in legacy user agents

Certain syntax constructs are known to cause especially subtle or serious problems in legacy user agents, and are therefore marked as non-conforming to help authors avoid them.

For example, this is why the U+0060 GRAVE ACCENT character (`) is not allowed in unquoted attributes. In certain legacy user agents, it is sometimes treated as a quote character.

Another example of this is the DOCTYPE, which is required to trigger no-quirks mode, because the behavior of legacy user agents in quirks mode is often largely undocumented.

Errors that risk exposing authors to security attacks

Certain restrictions exist purely to avoid known security problems.

For example, the restriction on using UTF-7 exists purely to avoid authors falling prey to a known cross-site-scripting attack using UTF-7.

Cases where the author's intent is unclear

Markup where the author's intent is very unclear is often made non-conforming. Correcting these errors early makes later maintenance easier.

For example, it is unclear whether the author intended the following to be an h1 heading or an h2 heading:

<h1>Contact details</h2>
Cases that are likely to be typos

When a user makes a simple typo, it is helpful if the error can be caught early, as this can save the author a lot of debugging time. This specification therefore usually considers it an error to use element names, attribute names, and so forth, that do not match the names defined in this specification.

For example, if the author typed <capton> instead of <caption>, this would be flagged as an error and the author could correct the typo immediately.

Errors that could interfere with new syntax in the future

In order to allow the language syntax to be extended in the future, certain otherwise harmless features are disallowed.

For example, "attributes" in end tags are ignored currently, but they are invalid, in case a future change to the language makes use of that syntax feature without conflicting with already-deployed (and valid!) content.

Some authors find it helpful to be in the practice of always quoting all attributes and always including all optional tags, preferring the consistency derived from such custom over the minor benefits of terseness afforded by making use of the flexibility of the HTML syntax. To aid such authors, conformance checkers can provide modes of operation wherein such conventions are enforced.

1.9.3 Restrictions on content models and on attribute values

This section is non-normative.

Beyond the syntax of the language, this specification also places restrictions on how elements and attributes can be specified. These restrictions are present for similar reasons:

Errors involving content with dubious semantics

To avoid misuse of elements with defined meanings, content models are defined that restrict how elements can be nested when such nestings would be of dubious value.

For example, this specification disallows nesting a section element inside a kbd element, since it is highly unlikely for an author to indicate that an entire section should be keyed in.

Errors that involve a conflict in expressed semantics

Similarly, to draw the author's attention to mistakes in the use of elements, clear contradictions in the semantics expressed are also considered conformance errors.

In the fragments below, for example, the semantics are nonsensical: a row cannot simultaneously be a cell, nor can a radio button be a progress bar.

<tr role="cell">
<input type=radio role=progressbar>

Another example is the restrictions on the content models of the ul element, which only allows li element children. Lists by definition consist just of zero or more list items, so if a ul element contains something other than an li element, it's not clear what was meant.

Cases where the default styles are likely to lead to confusion

Certain elements have default styles or behaviors that make certain combinations likely to lead to confusion. Where these have equivalent alternatives without this problem, the confusing combinations are disallowed.

For example, div elements are rendered as block boxes, and span elements as inline boxes. Putting a block box in an inline box is unnecessarily confusing; since either nesting just div elements, or nesting just span elements, or nesting span elements inside div elements all serve the same purpose as nesting a div element in a span element, but only the latter involves a block box in an inline box, the latter combination is disallowed.

Another example would be the way interactive content cannot be nested. For example, a button element cannot contain a textarea element. This is because the default behavior of such nesting interactive elements would be highly confusing to users. Instead of nesting these elements, they can be placed side by side.

Errors that indicate a likely misunderstanding of the specification

Sometimes, something is disallowed because allowing it would likely cause author confusion.

For example, setting the disabled attribute to the value "false" is disallowed, because despite the appearance of meaning that the element is enabled, it in fact means that the element is disabled (what matters for implementations is the presence of the attribute, not its value).

Errors involving limits that have been imposed merely to simplify the language

Some conformance errors simplify the language that authors need to learn.

For example, the area element's shape attribute, despite accepting both circ and circle values in practice as synonyms, disallows the use of the circ value, so as to simplify tutorials and other learning aids. There would be no benefit to allowing both, but it would cause extra confusion when teaching the language.

Errors that involve peculiarities of the parser

Certain elements are parsed in somewhat eccentric ways (typically for historical reasons), and their content model restrictions are intended to avoid exposing the author to these issues.

For example, a form element isn't allowed inside phrasing content, because when parsed as HTML, a form element's start tag will imply a p element's end tag. Thus, the following markup results in two paragraphs, not one:

<p>Welcome. <form><label>Name:</label> <input></form>

It is parsed exactly like the following:

<p>Welcome. </p><form><label>Name:</label> <input></form>
Errors that would likely result in scripts failing in hard-to-debug ways

Some errors are intended to help prevent script problems that would be hard to debug.

This is why, for instance, it is non-conforming to have two id attributes with the same value. Duplicate IDs lead to the wrong element being selected, with sometimes disastrous effects whose cause is hard to determine.

Errors that waste authoring time

Some constructs are disallowed because historically they have been the cause of a lot of wasted authoring time, and by encouraging authors to avoid making them, authors can save time in future efforts.

For example, a script element's src attribute causes the element's contents to be ignored. However, this isn't obvious, especially if the element's contents appear to be executable script — which can lead to authors spending a lot of time trying to debug the inline script without realising that it is not executing. To reduce this problem, this specification makes it non-conforming to have executable script in a script element when the src attribute is present. This means that authors who are validating their documents are less likely to waste time with this kind of mistake.

Errors that involve areas that affect authors migrating to and from XHTML

Some authors like to write files that can be interpreted as both XML and HTML with similar results. Though this practice is discouraged in general due to the myriad of subtle complications involved (especially when involving scripting, styling, or any kind of automated serialization), this specification has a few restrictions intended to at least somewhat mitigate the difficulties. This makes it easier for authors to use this as a transitionary step when migrating between HTML and XHTML.

For example, there are somewhat complicated rules surrounding the lang and xml:lang attributes intended to keep the two synchronized.

Another example would be the restrictions on the values of xmlns attributes in the HTML serialization, which are intended to ensure that elements in conforming documents end up in the same namespaces whether processed as HTML or XML.

Errors that involve areas reserved for future expansion

As with the restrictions on the syntax intended to allow for new syntax in future revisions of the language, some restrictions on the content models of elements and values of attributes are intended to allow for future expansion of the HTML vocabulary.

For example, limiting the values of the target attribute that start with an U+005F LOW LINE character (_) to only specific predefined values allows new predefined values to be introduced at a future time without conflicting with author-defined values.

Errors that indicate a mis-use of other specifications

Certain restrictions are intended to support the restrictions made by other specifications.

For example, requiring that attributes that take media queries use only valid media queries reinforces the importance of following the conformance rules of that specification.

Status: Last call for comments

This section is non-normative.

The following documents might be of interest to readers of this specification.

Character Model for the World Wide Web 1.0: Fundamentals [CHARMOD]

This Architectural Specification provides authors of specifications, software developers, and content developers with a common reference for interoperable text manipulation on the World Wide Web, building on the Universal Character Set, defined jointly by the Unicode Standard and ISO/IEC 10646. Topics addressed include use of the terms 'character', 'encoding' and 'string', a reference processing model, choice and identification of character encodings, character escaping, and string indexing.

Unicode Security Considerations [UTR36]

Because Unicode contains such a large number of characters and incorporates the varied writing systems of the world, incorrect usage can expose programs or systems to possible security attacks. This is especially important as more and more products are internationalized. This document describes some of the security considerations that programmers, system analysts, standards developers, and users should take into account, and provides specific recommendations to reduce the risk of problems.

Web Content Accessibility Guidelines (WCAG) 2.0 [WCAG]

Web Content Accessibility Guidelines (WCAG) 2.0 covers a wide range of recommendations for making Web content more accessible. Following these guidelines will make content accessible to a wider range of people with disabilities, including blindness and low vision, deafness and hearing loss, learning disabilities, cognitive limitations, limited movement, speech disabilities, photosensitivity and combinations of these. Following these guidelines will also often make your Web content more usable to users in general.

Authoring Tool Accessibility Guidelines (ATAG) 2.0 [ATAG]

This specification provides guidelines for designing Web content authoring tools that are more accessible for people with disabilities. An authoring tool that conforms to these guidelines will promote accessibility by providing an accessible user interface to authors with disabilities as well as by enabling, supporting, and promoting the production of accessible Web content by all authors.

User Agent Accessibility Guidelines (UAAG) 2.0 [UAAG]

This document provides guidelines for designing user agents that lower barriers to Web accessibility for people with disabilities. User agents include browsers and other types of software that retrieve and render Web content. A user agent that conforms to these guidelines will promote accessibility through its own user interface and through other internal facilities, including its ability to communicate with other technologies (especially assistive technologies). Furthermore, all users, not just users with disabilities, should find conforming user agents to be more usable.

2 Common infrastructure

2.1 Terminology

Status: Last call for comments

This specification refers to both HTML and XML attributes and IDL 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 IDL attributes for those defined on IDL interfaces. Similarly, the term "properties" is used for both JavaScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.

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

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

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

When an algorithm B says to return to another algorithm A, it implies that A called B. Upon returning to A, the implementation must continue from where it left off in calling B.

2.1.1 Resources

Status: Last call for comments

The specification uses the term supported when referring to whether a user agent has an implementation capable of decoding the semantics of an external resource. A format or type is said to be supported if the implementation can process an external resource of that format or type without critical aspects of the resource being ignored. Whether a specific resource is supported can depend on what features of the resource's format are in use.

For example, a PNG image would be considered to be in a supported format if its pixel data could be decoded and rendered, even if, unbeknownst to the implementation, the image also contained animation data.

A MPEG4 video file would not be considered to be in a supported format if the compression format used was not supported, even if the implementation could determine the dimensions of the movie from the file's metadata.

What some specifications, in particular the HTTP and URI specifications, refer to as a representation is referred to in this specification as a resource. [HTTP] [RFC3986]

The term MIME type is used to refer to what is sometimes called an Internet media type in protocol literature. The term media type in this specification is used to refer to the type of media intended for presentation, as used by the CSS specifications. [RFC2046] [MQ]

A string is a valid MIME type if it matches the media-type rule defined in section 3.7 "Media Types" of RFC 2616. In particular, a valid MIME type may include MIME type parameters. [HTTP]

A string is a valid MIME type with no parameters if it matches the media-type rule defined in section 3.7 "Media Types" of RFC 2616, but does not contain any U+003B SEMICOLON characters (;). In other words, if it consists only of a type and subtype, with no MIME Type parameters. [HTTP]

The term HTML MIME type is used to refer to the MIME types text/html and text/html-sandboxed.

A resource's critical subresources are those that the resource needs to have available to be correctly processed. Which resources are considered critical or not is defined by the specification that defines the resource's format. For CSS resources, only @import rules introduce critical subresources; other resources, e.g. fonts or backgrounds, are not.

2.1.2 XML

Status: Last call for comments

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 "HTML elements", when used in this specification, refers to any element in that namespace, and thus refers to both HTML and XHTML elements.

Except where 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.

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

The term XML MIME type is used to refer to the MIME types text/xml, application/xml, and any MIME type whose subtype ends with the four characters "+xml". [RFC3023]

2.1.3 DOM trees

Status: Last call for comments

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 the node's root element 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.

When an element's root element is the root element of a Document, it is said to be in a Document. An element is said to have been inserted into a document when its root element changes and is now the document's root element. Analogously, an element is said to have been removed from a document when its root element changes from being the document's root element to being another element.

A node's home subtree is the subtree rooted at that node's root element. When a node is in a Document, its home subtree is that Document's tree.

The Document of a Node (such as an element) is the Document that the Node's ownerDocument IDL attribute returns. When a Node is in a Document then that Document is always the Node's Document, and the Node's ownerDocument IDL attribute thus always returns that Document.

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

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

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

A content attribute is said to change value only if its new value is different than its previous value; setting an attribute to a value it already has does not change it.

2.1.4 Scripting

Status: Last call for comments

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".

An IDL 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 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. The term trusted event is used as defined by the DOM Events specification. [DOMEVENTS]

2.1.5 Plugins

Status: Last call for comments

The term plugin refers to a user-agent defined set of content handlers used by the user agent that can take part in the user agent's rendering of a Document object, but that neither act as child browsing contexts of the Document nor introduce any Node objects to the Document's DOM.

Typically such content handlers are provided by third parties, though a user agent can also designate built-in content handlers as plugins.

A user agent must not consider the types text/plain and application/octet-stream as having a registered plugin.

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

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

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

2.1.6 Character encodings

Status: Last call for comments. ISSUE-101 (us-ascii-ref) blocks progress to Last Call

The preferred MIME name of a character encoding is the name or alias labeled as "preferred MIME name" in the IANA Character Sets registry, if there is one, or the encoding's name, if none of the aliases are so labeled. [IANACHARSET]

An ASCII-compatible character encoding is a single-byte or variable-length encoding in which the bytes 0x09, 0x0A, 0x0C, 0x0D, 0x20 - 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A, and 0x61 - 0x7A, ignoring bytes that are the second and later bytes of multibyte sequences, all correspond to single-byte sequences that map to the same Unicode characters as those bytes in ANSI_X3.4-1968 (US-ASCII). [RFC1345]

This includes such encodings as Shift_JIS, HZ-GB-2312, and variants of ISO-2022, even though it is possible in these encodings for bytes like 0x70 to be part of longer sequences that are unrelated to their interpretation as ASCII. It excludes such encodings as UTF-7, UTF-16, GSM03.38, and EBCDIC variants.

The term Unicode character is used to mean a Unicode scalar value (i.e. any Unicode code point that is not a surrogate code point). [UNICODE]

2.2 Conformance requirements

Status: Last call for comments

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).

Conforming documents are those that comply with all the conformance criteria for documents. For readability, some of these conformance requirements are phrased as conformance requirements on authors; such requirements are implicitly requirements on documents: by definition, all documents are assumed to have had an author. (In some cases, that author may itself be a user agent — such user agents are subject to additional rules, as explained below.)

For example, if a requirement states that "authors must not use the foobar element", it would imply that documents are not allowed to contain elements named foobar.

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

Web browsers and other interactive user agents

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

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

Web browsers that support the HTML syntax must process documents labeled with an HTML MIME type as described in this specification, so that users can interact with them.

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

Unless explicitly stated, specifications that override the semantics of HTML elements do not override the requirements on DOM objects representing those elements. For example, the script element in the example above would still implement the HTMLScriptElement interface.

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. [COMPUTABLE])

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 with 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. However, authoring tools must not automatically misuse elements or encourage their users to do so.

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. This does not mean, though, that authoring tools can use address elements for any block of italics text (for instance); it just means that the authoring tool doesn't have to verify that when the user uses a tool for inserting contact information for a section, that the user really is doing that and not inserting something else instead.

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

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

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

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

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

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

Some conformance requirements are phrased as requirements on elements, attributes, methods or objects. Such requirements fall into two categories: those describing content model restrictions, and those describing implementation behavior. Those in the former category are requirements on documents and authoring tools. Those in the second category are requirements on user agents. Similarly, some conformance requirements are phrased as requirements on authors; such requirements are to be interpreted as conformance requirements on the documents that authors produce. (In other words, this specification does not distinguish between conformance criteria on authors and conformance criteria on documents.)

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.

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.

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

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

2.2.1 Dependencies

Status: Last call for comments

This specification relies on several other underlying specifications.

XML

Implementations that support the XHTML syntax must support some version of XML, as well as its corresponding namespaces specification, because that syntax uses an XML serialization with namespaces. [XML] [XMLNS]

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. [DOMCORE]

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. [DOMCORE] [DOMEVENTS]

In particular, the following features are defined in the DOM Core specification: [DOMCORE]

  • Attr interface
  • CDATASection interface
  • Comment interface
  • DOMImplementation interface
  • Document interface
  • DocumentFragment interface
  • DocumentType interface
  • DOMException interface
  • Element interface
  • Node interface
  • NodeList interface
  • ProcessingInstruction interface
  • Text interface
  • createDocument() method
  • getElementById() method
  • insertBefore() method
  • childNodes attribute
  • localName attribute
  • parentNode attribute
  • tagName attribute
  • textContent attribute

The following features are defined in the DOM Events specification: [DOMEVENTS]

  • Event interface
  • EventTarget interface
  • UIEvent interface
  • click event
  • DOMActivate event
  • target attribute

The following features are defined in the DOM Range specification: [DOMRANGE]

  • Range interface
  • deleteContents() method
  • selectNodeContents() method
  • setEnd() method
  • setStart() method
  • collapsed attribute
  • endContainer attribute
  • endOffset attribute
  • startContainer attribute
  • startOffset attribute
Web IDL

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

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

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

JavaScript

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

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

Media Queries

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

URIs, IRIs, IDNA

Implementations must support the semantics of URLs defined in the URI and IRI specifications, as well as the semantics of IDNA domain names defined in the Internationalizing Domain Names in Applications (IDNA) specification. [RFC3986] [RFC3987] [RFC3490]

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

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

2.2.2 Extensibility

Status: Last call for comments. ISSUE-41 (Decentralized-extensibility) blocks progress to Last Call

HTML has a wide number of extensibility mechanisms that can be used for adding semantics in a safe manner:


Vendor-specific proprietary user agent extensions to this specification are strongly discouraged. Documents must not use such extensions, as doing so reduces interoperability and fragments the user base, allowing only users of specific user agents to access the content in question.

If such extensions are nonetheless needed, e.g. for experimental purposes, then vendors are strongly urged to use one of the following extension mechanisms:

For markup-level features that can be limited to the XML serialization and need not be supported in the HTML serialization, vendors should use the namespace mechanism to define custom namespaces in which the non-standard elements and attributes are supported.

For markup-level features that are intended for use with the HTML syntax, extensions should be limited to new attributes of the form "_vendor-feature", where vendor is a short string that identifies the vendor responsible for the extension, and feature is the name of the feature. New element names should not be created. Using attributes for such extensions exclusively allows extensions from multiple vendors to co-exist on the same element, which would not be possible with elements. Using the "_vendor-feature" form allows extensions to be made without risk of conflicting with future additions to the specification.

For instance, a browser named "FerretBrowser" could use "ferret" as a vendor prefix, while a browser named "Mellblom Browser" could use "mb". If both of these browsers invented extensions that turned elements into scratch-and-sniff areas, an author experimenting with these features could write:

<p>This smells of lemons!
<span _ferret-smellovision _ferret-smellcode="LEM01"
      _mb-outputsmell _mb-smell="lemon juice"></span></p>

Attribute names starting with a U+005F LOW LINE character (_) are reserved for user agent use and are guaranteed to never be formally added to the HTML language.

Pages that use such attributes are by definition non-conforming.

For DOM extensions, e.g. new methods and IDL attributes, the new members should be prefixed by vendor-specific strings to prevent clashes with future versions of this specification.

All extensions must be defined so that the use of extensions neither contradicts nor causes the non-conformance of functionality defined in the specification.

For example, while strongly discouraged from doing so, an implementation "Foo Browser" could add a new IDL attribute "fooTypeTime" to a control's DOM interface that returned the time it took the user to select the current value of a control (say). On the other hand, defining a new control that appears in a form's elements array would be in violation of the above requirement, as it would violate the definition of elements given in this specification.


When vendor-neutral extensions to this specification are needed, either this specification can be updated accordingly, or an extension specification can be written that overrides the requirements in this specification. When someone applying this specification to their activities decides that they will recognize the requirements of such an extension specification, it becomes an applicable specification for the purposes of conformance requirements in this specification.


User agents must treat elements and attributes that they do not understand as semantically neutral; leaving them in the DOM (for DOM processors), and styling them according to CSS (for CSS processors), but not inferring any meaning from them.

When support for a feature is disabled (e.g. as an emergency measure to mitigate a security problem, or to aid in development, or for performance reasons), user agents must act as if they had no support for the feature whatsoever, and as if the feature was not mentioned in this specification. For example, if a particular feature is accessed via an attribute in a Web IDL interface, the attribute itself would be omitted from the objects that implement that interface — leaving the attribute on the object but making it return null or throw an exception is insufficient.

2.3 Case-sensitivity and string comparison

Status: Last call for comments

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

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

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

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

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

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

2.4 Common microsyntaxes

Status: Last call for comments

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.

Implementors are strongly urged to carefully examine any third-party libraries they might consider using to implement the parsing of syntaxes described below. For example, date libraries are likely to implement error handling behavior that differs from what is required in this specification, since error-handling behavior is often not defined in specifications that describe date syntaxes similar to those used in this specification, and thus implementations tend to vary greatly in how they handle errors.

2.4.1 Common parser idioms

Status: Last call for comments

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

The White_Space characters are those that have the Unicode property "White_Space" in the Unicode PropList.txt data file. [UNICODE]

This should not be confused with the "White_Space" value (abbreviated "WS") of the "Bidi_Class" property in the Unicode.txt data file.

The alphanumeric ASCII characters are those in the ranges U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z, U+0061 LATIN SMALL LETTER A to U+007A LATIN SMALL LETTER Z.

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

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

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

  2. Let result be the empty string.

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

  4. Return result.

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

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

When a user agent is to strip leading and trailing whitespace from a string, the user agent must remove all space characters that are at the start or end of the string.

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

2.4.2 Boolean attributes

Status: Last call for comments

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

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

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

2.4.3 Keywords and enumerated attributes

Status: Last call for comments

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

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

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

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

The empty string can be a valid keyword.

2.4.4 Numbers

Status: Last call for comments

2.4.4.1 Non-negative integers

Status: Last call for comments

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

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

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

  1. Let input be the string being parsed.

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

  3. Skip whitespace.

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

  5. If the character indicated by position is a U+002B PLUS SIGN character (+), advance position to the next character. (The "+" is ignored, but it is not conforming.)

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

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

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

  9. Return value.

2.4.4.2 Signed integers

Status: Last call for comments

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

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

The rules for parsing integers are similar to the rules for non-negative integers, and are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either 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 sign have the value "positive".

  4. Skip whitespace.

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

  6. 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.

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

    1. Advance position to the next character. (The "+" is ignored, but it is not conforming.)
    2. If position is past the end of input, return an error.
  7. If the character indicated by position is not one of U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then return an error.

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

  9. If sign is "positive", return value, otherwise return the result of subtracting value from zero.

2.4.4.3 Real numbers

Status: Last call for comments

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

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

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

The Infinity and Not-a-Number (NaN) values are not valid floating point numbers.

The best representation of the number n as a floating point number is the string obtained from applying the JavaScript operator ToString to n. The JavaScript operator ToString is not uniquely determined. When there are multiple possible strings that could be obtained from the JavaScript operator ToString for a particular value, the user agent must always return the same string for that value (though it may differ from the value used by other user agents).

The rules for parsing floating point number values are as given in the following algorithm. This algorithm must be aborted at the first step that returns something. This algorithm will return either a number or an error. Leading spaces are ignored. Trailing spaces and garbage characters are ignored.

  1. Let input be the string being parsed.

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

  3. Let value have the value 1.

  4. Let divisor have the value 1.

  5. Let exponent have the value 1.

  6. Skip whitespace.

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

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

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

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

  11. If position is past the end of input, jump to the step labeled conversion.
  12. If the character indicated by position is a U+002E FULL STOP (.), run these substeps:

    1. Advance position to the next character.

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

    3. Fraction loop: Multiply divisor by ten.

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

    6. If position is past the end of input, then jump to the step labeled conversion.

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

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

    1. Advance position to the next character.

    2. If position is past the end of input, then jump to the step labeled conversion.

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

      1. Change exponent to −1.
      2. Advance position to the next character.
      3. If position is past the end of input, then jump to the step labeled conversion.

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

      1. Advance position to the next character.
      2. If position is past the end of input, then jump to the step labeled conversion.

    4. If the character indicated by position is not one of U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then jump to the step labeled conversion.

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

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

  14. Conversion: Let S be the set of finite IEEE 754 single-precision floating point values except −0, but with two special values added: 2128 and −2128.

  15. Let rounded-value be the number in S that is closest to value, selecting the number with an even significand if there are two equally close values. (The two special values 2128 and −2128 are considered to have even significands for this purpose.)

  16. If rounded-value is 2128 or −2128, return an error.

  17. Return rounded-value.

2.4.4.4 Percentages and lengths

Status: Last call for comments

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

  1. Let input be the string being parsed.

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

  3. Skip whitespace.

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

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

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

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

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

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

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

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

    1. Advance position to the next character.

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

    3. Let divisor have the value 1.

    4. Fraction loop: Multiply divisor by ten.

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

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

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

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

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

  14. Return value as a length.

2.4.4.5 Lists of integers

Status: Last call for comments

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

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

  1. Let input be the string being parsed.

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

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

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

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

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

  7. Let negated be false.

  8. Let value be 0.

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

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

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

  12. Let bogus be false.

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

    A U+002D HYPHEN-MINUS character

    Follow these substeps:

    1. If got number is true, let finished be true.
    2. If finished is true, skip to the next step in the overall set of steps.
    3. If started is true, let negated be false.
    4. Otherwise, if started is false and if bogus is false, let negated be true.
    5. Let started be true.
    A character in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9)

    Follow these substeps:

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

    Follow these substeps:

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

    Follow these substeps:

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

    Follow these substeps:

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

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

  16. If negated is true, then negate value.

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

  18. Return the numbers list and abort.

2.4.4.6 Lists of dimensions

Status: Last call for comments

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

  1. Let raw input be the string being parsed.

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

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

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

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

    1. Let input be the token.

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

    3. Let value be the number 0.

    4. Let unit be absolute.

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

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

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

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

      2. Remove all space characters in s.

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

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

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

        3. Increment value by fraction.

    8. Skip whitespace.

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

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

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

  6. Return the list result.

2.4.5 Dates and times

Status: Last call for comments

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

The digits in the date and time syntaxes defined in this section must be characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), used to express numbers in base ten.

While the formats described here are intended to be subsets of the corresponding ISO8601 formats, this specification defines parsing rules in much more detail than ISO8601. Implementors are therefore encouraged to carefully examine any date parsing libraries before using them to implement the parsing rules described below; ISO8601 libraries might not parse dates and times in exactly the same manner. [ISO8601]

2.4.5.1 Months

Status: Last call for comments

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

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

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

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

  1. Let input be the string being parsed.

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

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

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

  5. Return year and month.

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

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

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

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

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

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

  6. Return year and month.

2.4.5.2 Dates

Status: Last call for comments

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

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

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

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

  1. Let input be the string being parsed.

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

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

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

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

  6. Return date.

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

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

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

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

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

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

  6. Return year, month, and day.

2.4.5.3 Times

Status: Last call for comments

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

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

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

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

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

  1. Let input be the string being parsed.

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

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

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

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

  6. Return time.

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

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

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

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

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

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

    1. Advance position to the next character in input.

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

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

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

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

  10. Return hour, minute, and second.

2.4.5.4 Local dates and times

Status: Last call for comments

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

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

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

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

  1. Let input be the string being parsed.

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

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

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

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

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

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

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

  9. Return date and time.

2.4.5.5 Global dates and times

Status: Last call for comments

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

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

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

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

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

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

Several things are notable about these dates:

The best representation of the global date and time string datetime is the valid global date and time string representing datetime with the last character of the string not being a U+005A LATIN CAPITAL LETTER Z character (Z), even if the time zone is UTC, and with a U+002D HYPHEN-MINUS character (-) representing the sign of the time-zone offset when the time zone is UTC.

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

  1. Let input be the string being parsed.

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

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

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

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

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

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

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

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

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

  11. Return time and timezone.

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

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

    1. Let timezonehours be 0.

    2. Let timezoneminutes be 0.

    3. Advance position to the next character in input.

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

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

    2. Advance position to the next character in input.

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

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

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

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

    Otherwise, fail.

  2. Return timezonehours and timezoneminutes.

2.4.5.6 Weeks

Status: Last call for comments

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

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

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

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

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

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

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

  1. Let input be the string being parsed.

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

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

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

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

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

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

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

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

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

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

2.4.5.7 Vaguer moments in time

Status: Last call for comments

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

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


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

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


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

  1. Let input be the string being parsed.

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

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

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

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

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

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

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

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

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

  9. If the date present and time present flags are both true, but position is beyond the end of input, then fail.

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

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

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

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

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

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

2.4.6 Colors

Status: Awaiting implementation feedback

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

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

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

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

  1. Let input be the string being parsed.

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

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

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

  5. Let result be a simple color.

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

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

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

  9. Return result.

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

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

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

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


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

  1. Let input be the string being parsed.

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

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

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

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

    1. Let result be a simple color.

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

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

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

    5. Return result.

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

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

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

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

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

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

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

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

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

  15. Let result be a simple color.

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

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

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

  19. Return result.


2.4.7 Space-separated tokens

Status: Last call for comments

A set of space-separated tokens is a string containing 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. Loop: If position is beyond the end of input, 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. Advance position so it points at the next character in input.

    3. Return to the step labeled loop.

  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 the step labeled loop.

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

2.4.8 Comma-separated tokens

Status: Last call for comments

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

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

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

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

  1. Let input be the string being parsed.

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

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

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

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

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

  7. Add s to tokens.

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

  9. Jump back to the step labeled token.

  10. Return tokens.

2.4.9 References

Status: Last call for comments

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 with type type in the document.

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

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

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

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

2.4.10 Media queries

Status: Last call for comments

A string is a valid media query if it matches the media_query_list production of the Media Queries specification. [MQ]

A string matches the environment of the user if it is the empty string, a string consisting of only space characters, or is a media query that matches the user's environment according to the definitions given in the Media Queries specification. [MQ]

2.5 URLs

Status: Last call for comments. ISSUE-56 (urls-webarch) blocks progress to Last Call

2.5.1 Terminology

Status: Last call for comments

A URL is a string used to identify a resource.

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

A string is a valid non-empty URL if it is a valid URL but it is not the empty string.

A string is a valid URL potentially surrounded by spaces if, after stripping leading and trailing whitespace from it, it is a valid URL.

A string is a valid non-empty URL potentially surrounded by spaces if, after stripping leading and trailing whitespace from it, it is a valid non-empty URL.

To parse a URL url into its component parts, the user agent must use the parse an address algorithm defined by the IRI specification. [RFC3987]

Parsing a URL can fail. If it does not, then it results in the following components, again as defined by the IRI specification:


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

  1. Let url be the URL being resolved.

  2. Let encoding be determined as follows:

    If the URL had a character encoding defined when the URL was created or defined
    The URL character encoding is as defined.
    If the URL came from a script (e.g. as an argument to a method)
    The URL character encoding is the script's URL character encoding.
    If the URL came from a DOM node (e.g. from an element)
    The node has a Document, and the URL character encoding is the document's character encoding.
  3. If encoding is a UTF-16 encoding, then change the value of encoding to UTF-8.

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

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

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

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

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

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

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

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

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

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

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

  5. Return the result of applying the resolve an address algorithm defined by the IRI specification to resolve url relative to base using encoding encoding. [RFC3987]

A URL is an absolute URL if resolving it results in the same output regardless of what it is resolved relative to, and that output is not a failure.

An absolute URL is a hierarchical URL if, when resolved and then parsed, there is a character immediately after the <scheme> component and it is a U+002F SOLIDUS character (/).

An absolute URL is an authority-based URL if, when resolved and then parsed, there are two characters immediately after the <scheme> component and they are both U+002F SOLIDUS characters (//).


This specification defines the URL about:legacy-compat as a reserved, though unresolvable, about: URI, for use in DOCTYPEs in HTML documents when needed for compatibility with XML tools. [ABOUT]

This specification defines the URL about:srcdoc as a reserved, though unresolvable, about: URI, that is used as the document's address of iframe srcdoc documents. [ABOUT]

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

2.5.2 Dynamic changes to base URLs

Status: Last call for comments

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

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

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

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

If the element is a hyperlink element

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

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

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

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

Otherwise

The element is not directly affected.

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

2.5.3 Interfaces for URL manipulation

Status: Last call for comments

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

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

Returns the current scheme of the underlying URL.

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

o . host [ = value ]

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

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

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

o . hostname [ = value ]

Returns the current host in the underlying URL.

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

o . port [ = value ]

Returns the current port in the underlying URL.

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

o . pathname [ = value ]

Returns the current path in the underlying URL.

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

o . search [ = value ]

Returns the current query component in the underlying URL.

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

o . hash [ = value ]

Returns the current fragment identifier in the underlying URL.

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


The attributes defined to be URL decomposition IDL 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 IDL 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 IDL attributes have similar requirements.

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

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

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

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

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

Attribute Component Getter Condition Prefix Suffix Setter Preprocessor Setter Condition
protocol <scheme> U+003A COLON (:) Remove all trailing U+003A COLON characters (:) The new value is not the empty string
host <hostport> input is an authority-based URL The new value is not the empty string and input is an authority-based URL
hostname <host> input is an authority-based URL Remove all leading U+002F SOLIDUS characters (/) The new value is not the empty string and input is an authority-based URL
port <port> input is an authority-based URL, and contained a <port> component (possibly an empty one) Remove all characters in the new value from the first that is not in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), if any. Remove any leading U+0030 DIGIT ZERO characters (0) in the new value. If the resulting string is empty, set it to a single U+0030 DIGIT ZERO character (0). input is an authority-based URL, and the new value, when interpretted as a base-ten integer, is less than or equal to 65535
pathname <path> input is a hierarchical URL If it has no leading U+002F SOLIDUS character (/), prepend a U+002F SOLIDUS character (/) to the new value input is hierarchical
search <query> input is a hierarchical URL, and contained a <query> component (possibly an empty one) U+003F QUESTION MARK (?) Remove one leading U+003F QUESTION MARK character (?), if any input is a hierarchical URL
hash <fragment> input contained a non-empty <fragment> component U+0023 NUMBER SIGN (#) Remove one leading U+0023 NUMBER SIGN character (#), if any

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

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

2.6 Fetching resources

Status: Last call for comments

When a user agent is to fetch a resource or URL, optionally from an origin origin, and optionally with a synchronous flag and/or a manual redirect flag, the following steps must be run. (When a URL is to be fetched, the URL identifies a resource to be obtained.)

  1. Generate the address of the resource from which Request-URIs are obtained as required by HTTP for the Referer (sic) header from the document's current address of the appropriate Document as given by the following list. [HTTP]

    When navigating
    The active document of the source browsing context.
    When fetching resources for an element
    The element's Document.
    When fetching resources in response to a call to an API
    The entry script's document.

    Remove any <fragment> component from the generated address of the resource from which Request-URIs are obtained.

    If the origin of the appropriate Document is not a scheme/host/port tuple, then the Referer (sic) header must be omitted, regardless of its value.

  2. If the algorithm was not invoked with the synchronous flag, perform the remaining steps asynchronously.

  3. This is the main step.

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

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

    For the purposes of the Referer (sic) header, use the address of the resource from which Request-URIs are obtained generated in the earlier step.

    For the purposes of the Origin header, if the fetching algorithm was explicitly initiated from an origin, then the origin that initiated the HTTP request is origin. Otherwise, this is a request from a "privacy-sensitive" context. [ORIGIN]

    If the resource is identified by the URL about:blank, then the resource is immediately available and consists of the empty string, with no metadata.

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

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

    2. Take ownership of the storage mutex.

    3. Update the cookies. [COOKIES]

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

  5. If the fetched resource is an HTTP redirect or equivalent, then:

    If the manual redirect flag is set

    Continue, using the fetched resource (the redirect) as the result of the algorithm.

    Otherwise

    First, apply any relevant requirements for redirects (such as showing any appropriate prompts). Then, redo main step, but using the target of the redirect as the resource to fetch, rather than the original resource.

    The HTTP specification requires that 301, 302, and 307 redirects, when applied to methods other than the safe methods, not be followed without user confirmation. That would be an appropriate prompt for the purposes of the requirement in the paragraph above. [HTTP]

  6. If the algorithm was not invoked with the synchronous flag: When the resource is available, or if there is an error of some description, queue a task that uses the resource as appropriate. If the resource can be processed incrementally, as, for instance, with a progressively interlaced JPEG or an HTML file, additional tasks may be queued to process the data as it is downloaded. The task source for these tasks is the networking task source.

    Otherwise, return the resource or error information to the calling algorithm.

If the user agent can determine the actual length of the resource being fetched for an instance of this algorithm, and if that length is finite, then that length is the file's size. Otherwise, the subject of the algorithm (that is, the resource being fetched) has no known size. (For example, the HTTP Content-Length header might provide this information.)

The user agent must also keep track of the number of bytes downloaded for each instance of this algorithm. This number must exclude any out-of-band metadata, such as HTTP headers.

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

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

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

2.6.1 Protocol concepts

Status: Last call for comments

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

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

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

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

Status: Last call for comments

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

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

User agents should warn the user that there is a potential problem whenever the user visits a page that the user has previously visited, if the page uses less secure encryption on the second visit.

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

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

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

If a user bookmarks a site that uses a CA-signed certificate, and then later revisits that site directly but the site has started using a self-signed certificate, the user agent could warn the user that a man-in-the-middle attack is likely underway, instead of simply acting as if the page was not encrypted.

2.6.3 Determining the type of a resource

Status: Last call for comments

The Content-Type metadata of a resource must be obtained and interpreted in a manner consistent with the requirements of the Content-Type Processing Model specification. [MIMESNIFF]

The sniffed type of a resource must be found in a manner consistent with the requirements given in the Content-Type Processing Model specification for finding the sniffed-type of the relevant sequence of octets. [MIMESNIFF]

The rules for sniffing images specifically and the rules for distingushing if a resource is text or binary are also defined in the Content-Type Processing Model specification. Both sets of rules return a MIME type as their result. [MIMESNIFF]

It is imperative that the rules in the Content-Type Processing Model specification be followed exactly. When a user agent uses different heuristics for content type detection than the server expects, security problems can occur. For more details, see the Content-Type Processing Model specification. [MIMESNIFF]

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

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

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

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

  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 encoding corresponding to 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 encoding corresponding to 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.

This requirement is a willful violation of the HTTP specification, motivated by the need for backwards compatibility with legacy content. [HTTP]

2.7 Common DOM interfaces

Status: Last call for comments

2.7.1 Reflecting content attributes in IDL attributes

Status: Last call for comments

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

In general, on getting, if the content attribute is not present, the IDL attribute must act as if the content attribute's value is the empty string; and on setting, if the content attribute is not present, it must first be added.

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

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

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

If a reflecting IDL 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 IDL attribute is a boolean attribute, then on getting the IDL attribute must return true if the content attribute is set, and false if it is absent. On setting, the content attribute must be removed if the IDL attribute is set to false, and must be set to the empty string if the IDL attribute is set to true. (This corresponds to the rules for boolean content attributes.)

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

If a reflecting IDL attribute is a signed integer type (long) that is limited to only non-negative numbers then, on getting, the content attribute must be parsed according to the rules for parsing non-negative integers, and if that is successful, and the value is in the range of the IDL attribute's type, the resulting value must be returned. If, on the other hand, it fails or returns an out of range value, or if the attribute is absent, the default value must be returned instead, or −1 if there is no default value. On setting, if the value is negative, 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 and then that string must be used as the new content attribute value.

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

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

If a reflecting IDL attribute is a floating point number type (float), 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 best representation of the number as a floating point number and then that string must be used as the new content attribute value.

The values Infinity and Not-a-Number (NaN) values throw an exception on setting, as defined earlier.

If a reflecting IDL attribute is of the type DOMTokenList or DOMSettableTokenList, then on getting it must return a DOMTokenList or DOMSettableTokenList object (as appropriate) whose underlying string is the element's corresponding content attribute. When the object mutates its underlying string, the content attribute must itself be immediately mutated. When the attribute is absent, then the string represented by the object is the empty string; when the object mutates this empty string, the user agent must add the corresponding content attribute, with its value set to the value it would have been set to after mutating the empty string. The same DOMTokenList or DOMSettableTokenList object must be returned every time for each attribute.

If an element with no attributes has its element.classList.remove() method invoked, the underlying string won't be changed, since the result of removing any token from the empty string is still the empty string. However, if the element.classList.add() method is then invoked, a class attribute will be added to the element with the value of the token to be added.

If a reflecting IDL 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 IDL attribute must return null.
  2. Let candidate be the element that the document.getElementById() method would find when called on the content attribute's document 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 IDL attribute, then the IDL 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 IDL attribute must be set to the empty string.

2.7.2 Collections

Status: Last call for comments

The HTMLCollection, HTMLAllCollection, HTMLFormControlsCollection, HTMLOptionsCollection, and HTMLPropertiesCollection 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.

2.7.2.1 HTMLCollection

Status: Last call for comments

The HTMLCollection interface represents a generic collection of elements.

interface HTMLCollection {
  readonly attribute unsigned long length;
  caller getter object item(in unsigned long index); // only returns Element
  caller getter object namedItem(in DOMString name); // only returns Element
};
collection . length

Returns the number of elements in the collection.

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

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

Returns null if index is out of range.

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

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

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

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

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

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

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

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

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

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

2.7.2.2 HTMLAllCollection

Status: Last call for comments

The HTMLAllCollection interface represents a generic collection of elements just like HTMLCollection, with the exception that its namedItem() method returns an HTMLCollection object when there are multiple matching elements.

interface HTMLAllCollection : HTMLCollection {
  // inherits length and item()
  caller getter object namedItem(in DOMString name); // overrides inherited namedItem()
  HTMLAllCollection tags(in DOMString tagName);
};
collection . length

Returns the number of elements in the collection.

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

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

Returns null if index is out of range.

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

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

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

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

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

collection = collection . tags(tagName)

Returns a collection that is a filtered view of the current collection, containing only elements with the given tag name.

The object's indices of the supported indexed properties and names of the supported named properties are as defined for HTMLCollection objects.

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

  1. Let collection be an HTMLAllCollection object rooted at the same node as the HTMLAllCollection object on which the method was invoked, whose filter matches only only elements that already match the filter of the HTMLAllCollection object on which the method was invoked and that are either:

  2. If, at the time the method is called, there is exactly one node in collection, then return that node and stop the algorithm.
  3. Otherwise, if, at the time the method is called, collection is empty, return null and stop the algorithm.
  4. Otherwise, return collection.

The tags(tagName) method must return an HTMLAllCollection rooted at the same node as the HTMLAllCollection object on which the method was invoked, whose filter matches only HTML elements whose local name is the tagName argument and that already match the filter of the HTMLAllCollection object on which the method was invoked. In HTML documents, the argument must first be converted to ASCII lowercase.

2.7.2.3 HTMLFormControlsCollection

Status: Last call for comments

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

interface HTMLFormControlsCollection : HTMLCollection {
  // inherits length and item()
  caller getter object namedItem(in DOMString name); // overrides inherited namedItem()
};

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

Returns the number of elements in the collection.

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

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

Returns null if index is out of range.

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

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

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

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

radioNodeList . value [ = value ]

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

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

The object's indices of the supported indexed properties are as defined for HTMLCollection objects.

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

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

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

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

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

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

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

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

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

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

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

2.7.2.4 HTMLOptionsCollection

Status: Last call for comments

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

interface HTMLOptionsCollection : HTMLCollection {
  // inherits item()
           attribute unsigned long length; // overrides inherited length
  caller getter object namedItem(in DOMString name); // overrides inherited namedItem()
  void add(in HTMLElement element, in optional HTMLElement before);
  void add(in HTMLElement element, in long before);
  void remove(in long index);
};
collection . length [ = value ]

Returns the number of elements in the collection.

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

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

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

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

Returns null if index is out of range.

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

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

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

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

collection . add(element [, before ] )

Inserts element before the node given by before.

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

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

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

The object's indices of the supported indexed properties are as defined for HTMLCollection objects.

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). Mutation events must be fired as if a DocumentFragment containing the new option elements had been inserted. 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 names of the supported named properties consist of the values of all the id and name attributes of all the elements represented by the collection.

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

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

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

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

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

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

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

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

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

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

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

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

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

  3. Remove element from its parent node.

2.7.3 DOMTokenList

Status: Last call for comments

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

DOMTokenList objects are always case-sensitive, even when the underlying string might ordinarily be treated in a case-insensitive manner.

interface DOMTokenList {
  readonly attribute unsigned long length;
  getter DOMString item(in unsigned long index);
  boolean contains(in DOMString token);
  void add(in DOMString token);
  void remove(in DOMString token);
  boolean toggle(in DOMString token);
  stringifier DOMString ();
};
tokenlist . length

Returns the number of tokens in the string.

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

Returns the token with index index. The tokens are returned in the order they are found in the underlying string.

Returns null if index is out of range.

hastoken = tokenlist . contains(token)

Returns true if the token is present; false otherwise.

Throws a SYNTAX_ERR exception if token is empty.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

tokenlist . add(token)

Adds token, unless it is already present.

Throws a SYNTAX_ERR exception if token is empty.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

tokenlist . remove(token)

Removes token if it is present.

Throws a SYNTAX_ERR exception if token is empty.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

hastoken = tokenlist . toggle(token)

Adds token if it is not present, or removes it if it is. Returns true if token is now present (it was added); returns false if it is not (it was removed).

Throws a SYNTAX_ERR exception if token is empty.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

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

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

The item(index) method must split the underlying string on spaces, preserving the order of the tokens as found in the underlying string, 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.

For example, if the string is "a b a c" then there are four tokens: the token with index 0 is "a", the token with index 1 is "b", the token with index 2 is "a", and the token with index 3 is "c".

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

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

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

  1. If the token argument is the empty string, then raise a SYNTAX_ERR exception and stop the algorithm.
  2. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  3. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  4. If the given token is a case-sensitive match for one of the tokens in the DOMTokenList object's underlying string then stop the algorithm.
  5. 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.
  6. 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 is the empty string, then raise a SYNTAX_ERR exception and stop the algorithm.
  2. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  3. Otherwise, remove the given token from the underlying string.

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

  1. If the token argument is the empty string, then raise a SYNTAX_ERR exception and stop the algorithm.
  2. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  3. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  4. If the given token is a case-sensitive match for 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.
  5. 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.
  6. Append the value of token to the end of the DOMTokenList object's underlying string.
  7. Return true.

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

2.7.4 DOMSettableTokenList

Status: Last call for comments

The DOMSettableTokenList interface is the same as the DOMTokenList interface, except that it allows the underlying string to be directly changed.

interface DOMSettableTokenList : DOMTokenList {
            attribute DOMString value;
};
tokenlist . value

Returns the underlying string.

Can be set, to change the underlying string.

An object implementing the DOMSettableTokenList interface must act as defined for the DOMTokenList interface, except for the value attribute defined here.

The value attribute must return the underlying string on getting, and must replace the underlying string with the new value on setting.

2.7.5 Safe passing of structured data

Status: Last call for comments

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

  1. Let input be the object being cloned.

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

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

  4. Return output.

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

If input is the undefined value

Return the undefined value.

If input is the null value

Return the null value.

If input is the false value

Return the false value.

If input is the true value

Return the true value.

If input is a Number object

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

If input is a String object

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

If input is a Date object

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

If input is a RegExp object

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

The value of the lastIndex property is not copied.

If input is a ImageData object

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

If input is a File object

Return a newly constructed File object corresponding to the same underlying data.

If input is a Blob object

Return a newly constructed Blob object corresponding to the same underlying data.

If input is a FileList object

Return a newly constructed FileList object containing a list of newly constructed File objects corresponding to the same underlying data as those in input, maintaining their relative order.

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

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

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

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

    This does not walk the prototype chain.

  5. Return output.

If input is another native object type (e.g. Error)
If input is a host object (e.g. a DOM node)

Throw a NOT_SUPPORTED_ERR exception and abort the overall structured clone algorithm.

2.7.6 DOMStringMap

Status: Last call for comments

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

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

interface DOMStringMap {
  getter DOMString (in DOMString name);
  setter void (in DOMString name, in DOMString value);
  creator void (in DOMString name, in DOMString value);
  deleter void (in DOMString name);
};

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

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

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

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

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

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

Given the following fragment and elements with similar constructions:

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

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

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

2.7.7 DOM feature strings

Status: Last call for comments

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

Authors are strongly discouraged from using these, as they are notoriously unreliable and imprecise. Authors are encouraged to rely on explicit feature testing or the graceful degradation behavior intrinsic to some of the features in this specification.

For historical reasons, user agents should return the true value when the hasFeature(feature, version) method of the DOMImplementation interface is invoked with feature set to either "HTML" or "XHTML" and version set to either "1.0" or "2.0".

2.7.8 Exceptions

Status: Last call for comments

The following are DOMException codes. [DOMCORE]

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

2.7.9 Garbage collection

Status: Last call for comments

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

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

2.8 Namespaces

Status: Last call for comments

The HTML namespace is: http://www.w3.org/1999/xhtml

The MathML namespace is: http://www.w3.org/1998/Math/MathML

The SVG namespace is: http://www.w3.org/2000/svg

The XLink namespace is: http://www.w3.org/1999/xlink

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

The XMLNS namespace is: http://www.w3.org/2000/xmlns/


Data mining tools and other user agents that perform operations on content without running scripts, evaluating CSS or XPath expressions, or otherwise exposing the resulting DOM to arbitrary content, may "support namespaces" by just asserting that their DOM node analogues are in certain namespaces, without actually exposing the above strings.

3 Semantics, structure, and APIs of HTML documents

Status: Last call for comments

3.1 Documents

Status: Last call for comments

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

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

Interactive user agents typically expose the document's current address in their user interface.

When a Document is created by a script using the createDocument() or createHTMLDocument() APIs, the document's address is the same as the document's address of the script's document.

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 and the case-sensitivity of some selectors.

3.1.1 Documents in the DOM

Status: Last call for comments

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 that the UA supports.

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

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

[OverrideBuiltins]
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
  getter any (in DOMString name);
           attribute DOMString title;
           attribute DOMString dir;
           attribute HTMLElement body;
  readonly attribute HTMLHeadElement head;
  readonly attribute HTMLCollection images;
  readonly attribute HTMLCollection embeds;
  readonly attribute HTMLCollection plugins;
  readonly attribute HTMLCollection links;
  readonly attribute HTMLCollection forms;
  readonly attribute HTMLCollection scripts;
  NodeList getElementsByName(in DOMString elementName);
  NodeList getElementsByClassName(in DOMString classNames);

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

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

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

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.

3.1.2 Security

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

3.1.3 Resource metadata management

Status: Last call for comments

document . URL

Returns the document's address.

document . referrer

Returns the address of the Document from which the user navigated to this one, unless it was blocked or there was no such document, in which case it returns the empty string.

The noreferrer link type can be used to block the referrer.

The URL attribute must return the document's address.

The referrer attribute must return either the current address of the active document of the source browsing context at the time the navigation was started (that is, the page which navigated the browsing context to the current document), with any <fragment> component removed; 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 IDL attribute will match the Referer (sic) header that was sent when fetching the current page.

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


document . cookie [ = value ]

Returns the HTTP cookies that apply to the Document. If there are no cookies or cookies can't be applied to this resource, the empty string will be returned.

Can be set, to add a new cookie to the element's set of HTTP cookies.

If the contents are sandboxed into a unique origin (in an iframe with the sandbox attribute) or the resource was labeled as text/html-sandboxed, a SECURITY_ERR exception will be thrown on getting and setting.

The cookie attribute represents the cookies of the resource from which the Document was created.

Some Document objects are cookie-free Document objects. Any Document object created by the createDocument() or createHTMLDocument() factory methods is a cookie-free Document object. Any Document whose address does not use a server-based naming authority is a cookie-free Document object. Other specifications can also define Document objects as being cookie-free Document objects.

On getting, if the document is a cookie-free Document object, then the user agent must return the empty string. Otherwise, if the Document's origin is not a scheme/host/port tuple, the user agent must raise a SECURITY_ERR exception. Otherwise, the user agent must first obtain the storage mutex and then return the cookie-string for the document's address for a "non-HTTP" API. [COOKIES]

On setting, if the document is a cookie-free Document object, then the user agent must do nothing. Otherwise, if the Document's origin is not a scheme/host/port tuple, the user agent must raise a SECURITY_ERR exception. Otherwise, the user agent must obtain the storage mutex and then act as it would when receiving a set-cookie-string for the document's address via a "non-HTTP" API, consisting of the new value. [COOKIES]

Since the cookie attribute is accessible across frames, the path restrictions on cookies are only a tool to help manage which cookies are sent to which parts of the site, and are not in any way a security feature.


document . lastModified

Returns the date of the last modification to the document, as reported by the server, in the form "MM/DD/YYYY hh:mm:ss", in the user's local time zone.

If the last modification date is not known, the current time is returned instead.

The lastModified attribute, on getting, must return the date and time of the Document's source file's last modification, in the user's local time zone, in the following format:

  1. The month component of the date.
  2. A U+002F SOLIDUS character (/).
  3. The day component of the date.
  4. A U+002F SOLIDUS character (/).
  5. The year component of the date.
  6. A U+0020 SPACE character.
  7. The hours component of the time.
  8. A U+003A COLON character (:).
  9. The minutes component of the time.
  10. A U+003A COLON character (:).
  11. The seconds component of the time.

All the numeric components above, other than the year, must be given as two digits in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) representing the number in base ten, zero-padded if necessary. The year must be given as the shortest possible string of four or more digits in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) representing the number in base ten, zero-padded if necessary.

The Document's source file's last modification date and time must be derived from relevant features of the networking protocols used, e.g. from the value of the HTTP Last-Modified header of the document, or from metadata in the file system for local files. If the last modification date and time are not known, the attribute must return the current date and time in the above format.


document . compatMode

In a conforming document, returns the string "CSS1Compat". (In quirks mode documents, returns the string "BackCompat", but a conforming document can never trigger quirks mode.)

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

The compatMode IDL 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".


document . charset [ = value ]

Returns the document's character encoding.

Can be set, to dynamically change the document's character encoding.

New values that are not IANA-registered aliases supported by the user agent are ignored.

document . characterSet

Returns the document's character encoding.

document . defaultCharset

Returns what might be the user agent's default character encoding. (The user agent might return another character encoding altogether, e.g. to protect the user's privacy, or if the user agent doesn't use a single default encoding.)

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

The charset IDL 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 supported by the user agent, the document's character encoding must be set to that character encoding. (Otherwise, nothing happens.)

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

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


document . readyState

Returns "loading" while the Document is loading, and "complete" once it has loaded.

The readystatechange event fires on the Document object when this value changes.

Each document has a current document readiness. When a Document object is created, it must have its current document readiness set to the string "loading" if the document is associated with an HTML parser or an XML parser, or to the string "complete" otherwise. Various algorithms during page loading affect this value. When the value is set, the user agent must fire a simple event named readystatechange at the Document object.

A Document is said to have an active parser if it is associated with an HTML parser or an XML parser that has not yet been stopped or aborted.

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

3.1.4 DOM tree accessors

Status: Last call for comments

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.


document . head

Returns the head element.

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 head attribute, on getting, must return the head element of the document (a head element or null).


document . title [ = value ]

Returns the document's title, as given by the title element.

Can be set, to update the document's title. If there is no head element, the new value is ignored.

In SVG documents, the SVGDocument interface's title attribute takes precedence.

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

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

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

  2. Otherwise, let value be 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.

  3. Replace any sequence of one or more consecutive space characters in value with a single U+0020 SPACE character.

  4. Remove any leading or trailing space characters in value.

  5. Return value.

On setting, the following algorithm must be run. Mutation events must be fired as appropriate.

  1. If the root element is an svg element in the "http://www.w3.org/2000/svg" namespace, and the user agent supports SVG, then the setter must defer to the setter for the IDL attribute of the same name on the SVGDocument interface (if it is readonly, then this will raise an exception). Stop the algorithm here. [SVG]

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

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


document . body [ = value ]

Returns the body element.

Can be set, to replace the body element.

If the new value is not a body or frameset element, this will throw a HIERARCHY_REQUEST_ERR exception.

The body element of a document is the first child of the html element that is either a body element or a frameset element. If there is no such element, it is null. If the body element is null, then when the specification requires that events be fired at "the body element", they must instead be fired at the Document object.

The body attribute, on getting, must return the body element of the document (either a body element, a frameset element, or null). On setting, the following algorithm must be run:

  1. If the new value is not a body or frameset element, then raise a HIERARCHY_REQUEST_ERR exception and abort these steps.
  2. Otherwise, if the new value is the same as the body element, do nothing. Abort these steps.
  3. Otherwise, if the body element is not null, then replace that element with the new value in the DOM, as if the root element's replaceChild() method had been called with the new value and the incumbent body element as its two arguments respectively, then abort these steps.
  4. Otherwise, the body element is null. Append the new value to the root element.

document . images

Returns an HTMLCollection of the img elements in the Document.

document . embeds
document . plugins

Return an HTMLCollection of the embed elements in the Document.

document . links

Returns an HTMLCollection of the a and area elements in the Document that have href attributes.

document . forms

Return an HTMLCollection of the form elements in the Document.

document . scripts

Return an HTMLCollection of the script elements in the Document.

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

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

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

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

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

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


collection = document . getElementsByName(name)

Returns a NodeList of elements in the Document that have a name attribute with the value name.

collection = document . getElementsByClassName(classes)
collection = element . getElementsByClassName(classes)

Returns a NodeList of the elements in the object on which the method was invoked (a Document or an Element) that have all the classes given by classes.

The classes argument is interpreted as a space-separated list of classes.

The getElementsByName(name) method takes a string name, and must return a live NodeList containing all the HTML elements in that document that have a name attribute whose value is equal to the name argument (in a case-sensitive manner), in tree order. When the method is invoked on a Document object again with the same argument, the user agent may return the same as the object returned by the earlier call. In other cases, a new NodeList object must be returned.

The getElementsByClassName(classNames) method takes a string that contains a set of space-separated tokens representing classes. When called, the method must return a live NodeList object containing all the elements in the document, in tree order, that have all the classes specified in that argument, having obtained the classes by splitting a string on spaces. (Duplicates are ignored.) If there are no tokens specified in the argument, then the method must return an empty NodeList. If the document is in quirks mode, then the comparisons for the classes must be done in an ASCII case-insensitive manner, otherwise, the comparisons must be done in a case-sensitive manner. When the method is invoked on a Document object again with the same argument, the user agent may return the same object as the object returned by the earlier call. In other cases, a new NodeList object must be returned.

The getElementsByClassName(classNames) method on the HTMLElement interface must return a live NodeList with the nodes that the HTMLDocument getElementsByClassName() method would return when passed the same argument(s), excluding any elements that are not descendants of the HTMLElement object on which the method was invoked. When the method is invoked on an HTMLElement object again with the same argument, the user agent may return the same object as the object returned by the earlier call. In other cases, a new NodeList object must be returned.

HTML, SVG, and MathML elements define which classes they are in by having an attribute with no namespace with the name class containing a space-separated list of classes to which the element belongs. Other specifications may also allow elements in their namespaces to be labeled as being in specific classes.

Given the following XHTML fragment:

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

A call to document.getElementById('example').getElementsByClassName('aaa') would return a NodeList with the two paragraphs p1 and p2 in it.

A call to getElementsByClassName('ccc bbb') would only return one node, however, namely p3. A call to document.getElementById('example').getElementsByClassName('bbb  ccc ') would return the same thing.

A call to getElementsByClassName('aaa,bbb') would return no nodes; none of the elements above are in the "aaa,bbb" class.


The HTMLDocument interface supports named properties. The names of the supported named properties at any moment consist of the values of the name content attributes of all the applet, embed, form, iframe, img, and fallback-free object elements in the Document that have name content attributes, and the values of the id content attributes of all the applet and fallback-free object elements in the Document that have id content attributes, and the values of the id content attributes of all the img elements in the Document that have both name content attributes and id content attributes.

When the HTMLDocument object is indexed for property retrieval using a name name, then the user agent must return the value obtained using the following steps:

  1. Let elements be the list of named elements with the name name in the Document.

    There will be at least one such element, by definition.

  2. If elements has only one element, and that element is an iframe element, then return the WindowProxy object of the nested browsing context represented by that iframe element, and abort these steps.

  3. Otherwise, if elements has only one element, return that element and abort these steps.

  4. Otherwise return an HTMLCollection rooted at the Document node, whose filter matches only named elements with the name name.

Named elements with the name name, for the purposes of the above algorithm, are those that are either:

An object element is said to be fallback-free if it has no object or embed descendants.


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

3.1.5 Creating documents

Status: Last call for comments

XML documents can be created from script using the createDocument() method on the DOMImplementation interface.

HTML documents can be created using the createHTMLDocument() method:

[Supplemental, NoInterfaceObject]
interface DOMHTMLImplementation {
  Document createHTMLDocument(in DOMString title);
};
DOMImplementation implements DOMHTMLImplementation;
document = document . implementation . createHTMLDocument( title )

Returns a new Document, with a basic DOM already constructed with an appropriate title element.

The createHTMLDocument(title) method, when invoked, must run the following steps:

  1. Let doc be a newly created Document object.

  2. Mark doc as being an HTML document.

  3. Create a DocumentType node with the name attribute set to the string "html", and the other attributes specific to DocumentType objects set to the empty string, null, and empty lists, as appropriate. Append the newly created node to doc.

  4. Create an html element, and append it to doc.

  5. Create a head element, and append it to the html element created in the previous step.

  6. Create a title element, and append it to the head element created in the previous step.

  7. Create a Text node, and set its data attribute to the string given by the method's argument (which could be the empty string). Append it to the title element created in the previous step.

  8. Create a body element, and append it to the html element created in the earlier step.

  9. Return doc.

3.2 Elements

Status: Last call for comments

3.2.1 Semantics

Status: Last call for comments. ISSUE-41 (Decentralized-extensibility) blocks progress to Last Call

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, or attribute values for purposes other than their appropriate intended semantic purpose. Authors must not use elements, attributes, or attribute values that are not permitted by this specification or other applicable specifications.

For example, the following document is non-conforming, despite being syntactically correct:

<!DOCTYPE HTML>
<html lang="en-GB">
 <head> <title> Demonstration </title> </head>
 <body>
  <table>
   <tr> <td> My favourite animal is the cat. </td> </tr>
   <tr>
    <td>
     —<a href="http://example.org/~ernest/"><cite>Ernest</cite></a>,
     in an essay from 1992
    </td>
   </tr>
  </table>
 </body>
</html>

...because the data placed in the cells is clearly not tabular data (and the cite element mis-used). A corrected version of this document might be:

<!DOCTYPE HTML>
<html lang="en-GB">
 <head> <title> Demonstration </title> </head>
 <body>
  <blockquote>
   <p> My favourite animal is the cat. </p>
  </blockquote>
  <p>
   —<a href="http://example.org/~ernest/">Ernest</a>,
   in an essay from 1992
  </p>
 </body>
</html>

This next document fragment, intended to represent the heading of a corporate site, is similarly non-conforming because the second line is not intended to be a heading of a subsection, but merely a subheading or subtitle (a subordinate heading for the same section).

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

The hgroup element is intended for these kinds of situations:

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

In the next example, there is a non-conforming attribute value ("carpet") and a non-conforming attribute ("texture"), which is not permitted by this specification:

<label>Carpet: <input type="carpet" name="c" texture="deep pile"></label>

Here would be an alternative and correct way to mark this up:

<label>Carpet: <input type="text" class="carpet" name="c" data-texture="deep pile"></label>

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.

3.2.2 Elements in the DOM

Status: Last call for comments

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

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

For example, an ol element represents an ordered list.

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

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

  // dynamic markup insertion
           attribute DOMString innerHTML;
           attribute DOMString outerHTML;
  void insertAdjacentHTML(in DOMString position, in DOMString text);

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

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

  // command API
  readonly attribute DOMString commandType;
  readonly attribute DOMString label;
  readonly attribute DOMString icon;
  readonly attribute boolean disabled;
  readonly attribute boolean checked;

  // styling
  readonly attribute CSSStyleDeclaration style;

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

interface HTMLUnknownElement : HTMLElement { };

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.

The HTMLUnknownElement interface must be used for HTML elements that are not defined by this specification (or other applicable specifications).

3.2.3 Global attributes

Status: Last call for comments

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


The following event handler content attributes may be specified on any HTML element:

The attributes marked with an asterisk have a different meaning when specified on body elements as those elements expose event handlers of the Window object with the same names.

While these attributes apply to all elements, they are not useful on all elements. For example, only media elements will ever receive a volumechange event fired by the user agent.


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.


To enable assistive technology products to expose a more fine-grained interface than is otherwise possible with HTML elements and attributes, a set of annotations for assistive technology products can be specified (the ARIA role and aria-* attributes).

3.2.3.1 The id attribute

Status: Last call for comments

The id attribute specifies its element's unique identifier (ID). The value must be unique amongst all the IDs in the element's home subtree and must contain at least one character. The value must not contain any space characters.

An element's unique identifier can be used for a variety of purposes, most notably as a way to link to specific parts of a document using fragment identifiers, as a way to target an element when scripting, and as a way to style a specific element from CSS.

If the value is not the empty string, user agents must associate the element with the given value (exactly, including any space characters) for the purposes of ID matching within the element's home subtree (e.g. for selectors in CSS or for the getElementById() method in the DOM).

Identifiers are opaque strings. Particular meanings should not be derived from the value of the id attribute.

This specification doesn't preclude an element having multiple IDs, if other mechanisms (e.g. DOM Core methods) can set an element's ID in a way that doesn't conflict with the id attribute.

The id IDL attribute must reflect the id content attribute.

3.2.3.2 The title attribute

Status: Last call for comments

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

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

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

Caution is advised with respect to the use of newlines in title attributes.

For instance, the following snippet actually defines an abbreviation's expansion with a line break in it:

<p>My logs show that there was some interest in <abbr title="Hypertext
Transport Protocol">HTTP</abbr> today.</p>

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


The title IDL attribute must reflect the title content attribute.

3.2.3.3 The lang and xml:lang attributes

Status: Last call for comments

The lang attribute (in no namespace) 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 BCP 47 language tag, or the empty string. Setting the attribute to the empty string indicates that the primary language is unknown. [BCP47]

The lang attribute in the XML namespace is defined in XML. [XML]

If these attributes are omitted from an element, then the language of this element is the same as the language of its parent element, if any.

The lang attribute in no namespace may be used on any HTML element.

The lang attribute in the XML namespace may be used on HTML elements in XML documents, as well as elements in other namespaces if the relevant specifications allow it (in particular, MathML and SVG allow lang attributes in the XML namespace to be specified on their elements). If both the lang attribute in no namespace and the lang attribute in the XML namespace are specified on the same element, they must have exactly the same value when compared in an ASCII case-insensitive manner.

Authors must not use the lang attribute in the XML namespace on HTML elements in HTML documents. To ease migration to and from XHTML, authors may specify an attribute in no namespace with no prefix and with the literal localname "xml:lang" on HTML elements in HTML documents, but such attributes must only be specified if a lang attribute in no namespace is also specified, and both attributes must have the same value when compared in an ASCII case-insensitive manner.

The attribute in no namespace with no prefix and with the literal localname "xml:lang" has no effect on language processing.


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 a lang attribute in the XML namespace set or is an HTML element and has a lang in no namespace attribute set. That attribute specifies the language of the node (regardless of its value).

If both the lang attribute in no namespace and the lang attribute in the XML namespace are set on an element, user agents must use the lang attribute in the XML namespace, and the lang attribute in no namespace must be ignored for the purposes of determining the element's language.

If none of the node's ancestors, including the root element, have either attribute set, but there is a pragma-set default language set, then that is the language of the node. If there is no pragma-set default language set, then language information from a higher-level protocol (such as HTTP), if any, must be used as the final fallback language instead. In the absence of any such language information, and in cases where the higher-level protocol reports multiple languages, the language of the node is unknown, and the corresponding language tag is the empty string.

If the resulting value is not a recognized language tag, then it must be treated as an unknown language having the given language tag, distinct from all other languages. For the purposes of round-tripping or communicating with other services that expect language tags, user agents should pass unknown language tags through unmodified.

Thus, for instance, an element with lang="xyzzy" would be matched by the selector :lang(xyzzy) (e.g. in CSS), but it would not be matched by :lang(abcde), even though both are equally invalid. Similarly, if a Web browser and screen reader working in unison communicated about the language of the element, the browser would tell the screen reader that the language was "xyzzy", even if it knew it was invalid, just in case the screen reader actually supported a language with that tag after all.

If the resulting value is the empty string, then it must be interpreted as meaning that the language of the node is explicitly unknown.


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 IDL attribute must reflect the lang content attribute in no namespace.

3.2.3.4 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.

3.2.3.5 The dir attribute

Status: Last call for comments

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 invalid value default and no missing value default.

The processing of this attribute is primarily performed by the presentation layer. For example, the rendering section in this specification defines a mapping from this attribute to the CSS 'direction' and 'unicode-bidi' properties, and CSS defines rendering in terms of those properties.

The directionality of an element, which is used in particular by the canvas element's text rendering API, is either 'ltr' or 'rtl'. If the user agent supports CSS and the 'direction' property on this element has a computed value of either 'ltr' or 'rtl', then that is the directionality of the element. Otherwise, if the element is being rendered, then the directionality of the element is the directionality used by the presentation layer, potentially determined from the value of the dir attribute on the element. Otherwise, if the element's dir attribute has the state ltr, the element's directionality is 'ltr' (left-to-right); if the attribute has the state rtl, the element's directionality is 'rtl' (right-to-left); and otherwise, the element's directionality is the same as its parent element, or 'ltr' if there is no parent element.


document . dir [ = value ]

Returns the html element's dir attribute's value, if any.

Can be set, to either "ltr" or "rtl", to replace the html element's dir attribute's value.

If there is no html element, returns the empty string and ignores new values.

The dir IDL attribute on an element must reflect the dir content attribute of that element, limited to only known values.

The dir IDL attribute on HTMLDocument objects must reflect the dir content attribute of the html element, if any, limited to only known values. If there is no such element, then the attribute must return the empty string and do nothing on setting.

Authors are strongly encouraged to use the dir attribute to indicate text direction rather than using CSS, since that way their documents will continue to render correctly even in the absence of CSS (e.g. as interpreted by search engines).

3.2.3.6 The class attribute

Status: Last call for comments

Every HTML element may have a class attribute specified.

The attribute, if specified, must have a value that is a set of 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. (Duplicates are ignored.)

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

There are no additional restrictions on the tokens authors can use in the class attribute, but authors are encouraged to use values that describe the nature of the content, rather than values that describe the desired presentation of the content.


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

3.2.3.7 The style attribute

Status: Last call for comments

All HTML elements may have the style content attribute set. This is a CSS styling attribute as defined by the CSS Styling Attribute Syntax specification. [CSSATTR]

In user agents that support CSS, the attribute's value must be parsed when the attribute is added or has its value changed, according to the rules given for CSS styling attributes. [CSSATTR]

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

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


element . style

Returns a CSSStyleDeclaration object for the element's style attribute.

The style IDL 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. The same object must be returned each time. [CSSOM]

In the following example, the words that refer to colors are marked up using the span element and the style attribute to make those words show up in the relevant colors in visual media.

<p>My sweat suit is <span style="color: green; background:
transparent">green</span> and my eyes are <span style="color: blue;
background: transparent">blue</span>.</p>
3.2.3.8 Embedding custom non-visible data

Status: Last call for comments

A custom data attribute is an attribute in no namespace whose name starts with the string "data-", has at least one character after the hyphen, is XML-compatible, and contains no characters in the range U+0041 to U+005A (LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).

All attributes on HTML elements in HTML documents get ASCII-lowercased automatically, so the restriction on ASCII uppercase letters doesn't affect such documents.

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

These attributes are not intended for use by software that is independent of the site that uses the attributes.

For instance, a site about music could annotate list items representing tracks in an album with custom data attributes containing the length of each track. This information could then be used by the site itself to allow the user to sort the list by track length, or to filter the list for tracks of certain lengths.

<ol>
 <li data-length="2m11s">Beyond The Sea</li>
 ...
</ol>

It would be inappropriate, however, for the user to use generic software not associated with that music site to search for tracks of a certain length by looking at this data.

This is because these attributes are intended for use by the site's own scripts, and are not a generic extension mechanism for publicly-usable metadata.

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


element . dataset

Returns a DOMStringMap object for the element's data-* attributes.

Hyphenated names become camel-cased. For example, data-foo-bar="" becomes element.dataset.fooBar.

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

The algorithm for getting the list of name-value pairs
  1. Let list be an empty list of name-value pairs.
  2. For each content attribute on the element whose first five characters are the string "data-" and whose remaining characters (if any) do not include any characters in the range U+0041 to U+005A (LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z), add a name-value pair to list whose name is the attribute's name with the first five characters removed and whose value is the attribute's value.
  3. For each name on the list, for each U+002D HYPHEN-MINUS character (-) in the name that is followed by a character in the range U+0061 to U+007A (U+0061 LATIN SMALL LETTER A to U+007A LATIN SMALL LETTER Z), remove the U+002D HYPHEN-MINUS character (-) and replace the character that followed it by the same character converted to ASCII uppercase.
  4. Return list.
The algorithm for setting names to certain values
  1. Let name be the name passed to the algorithm.
  2. Let value be the value passed to the algorithm.
  3. If name contains a U+002D HYPHEN-MINUS character (-) followed by a character in the range U+0061 to U+007A (U+0061 LATIN SMALL LETTER A to U+007A LATIN SMALL LETTER Z), throw a SYNTAX_ERR exception and abort these steps.
  4. For each character in the range U+0041 to U+005A (U+0041 LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z) in name, insert a U+002D HYPHEN-MINUS character (-) before the character and replace the character with the same character converted to ASCII lowercase.
  5. Insert the string data- at the front of name.
  6. 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 name passed to the algorithm.
  2. If name contains a U+002D HYPHEN-MINUS character (-) followed by a character in the range U+0061 to U+007A (U+0061 LATIN SMALL LETTER A to U+007A LATIN SMALL LETTER Z), throw a SYNTAX_ERR exception and abort these steps.
  3. For each character in the range U+0041 to U+005A (U+0041 LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z) in name, insert a U+002D HYPHEN-MINUS character (-) before the character and replace the character with the same character converted to ASCII lowercase.
  4. Insert the string data- at the front of name.
  5. Remove the attribute with the name name, if such an attribute exists. Do nothing otherwise.

The same object must be returned each time.

If a Web page wanted an element to represent a space ship, e.g. as part of a game, it would have to use the class attribute along with data-* attributes:

<div class="spaceship" data-ship-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.shipId].fire()">
  Fire
 </button>
</div>

Notice how the hyphenated attribute name becomes capitalized in the API.

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.

JavaScript libraries may use the custom data attributes, as they are considered to be part of the page on which they are used. Authors of libraries that are reused by many authors are encouraged to include their name in the attribute names, to reduce the risk of clashes.

For example, a library called "DoQuery" could use attribute names like data-doquery-range, and a library called "jJo" could use attributes names like data-jjo-range.

3.2.4 Element definitions

Status: Last call for comments

Each element in this specification has a definition that includes the following information:

Categories
A list of categories to which the element belongs. These are used when defining the content models for each element.
Contexts in which this element may be used
A non-normative description of where the element can be used. This information is redundant with the content models of elements that allow this one as a child, and is provided only as a convenience.
Content model
A normative description of what content must be included as children and descendants of the element.
Content attributes
A normative list of attributes that may be specified on the element (except where otherwise disallowed).
DOM interface
A normative definition of a DOM interface that such elements must implement.

This is then followed by a description of what the element represents, along with any additional normative conformance criteria that may apply to authors and implementations. Examples are sometimes also included.

3.2.4.1 Attributes

Status: Last call for comments

Except where otherwise specified, attributes on HTML elements may have any string value, including the empty string. Except where explicitly stated, there is no restriction on what text can be specified in such attributes.

3.2.5 Content models

Status: Last call for comments

Each element defined in this specification has a content model: a description of the element's expected contents. An HTML element must have contents that match the requirements described in the element's content model.

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

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

Inter-element whitespace, comment nodes, and processing instruction nodes must be ignored when establishing whether an element's contents match the element's 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 HTML elements 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.

For example, the Atom specification defines a content element. When its type attribute has the value xhtml, the Atom specification requires that it contain a single HTML div element. Thus, a div element is allowed in that context, even though this is not explicitly normatively stated by this specification. [ATOM]

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

For example, creating a td element and storing it in a global variable in a script is conforming, even though td elements are otherwise only supposed to be used inside tr elements.

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

Status: Last call for comments

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

Some elements also fall into other categories, which are defined in other parts of this specification.

These categories are related as follows:

Sectioning content, heading content, phrasing content, and
  embedded content are all types of flow content. Embedded content is
  also a type of phrasing content.

In addition, certain elements are categorized as form-associated elements and further subcategorized to define their role in various form-related processing models.

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

3.2.5.1.1 Metadata content

Status: Last call for comments

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

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

Thus, in the XML serialization, one can use RDF, like this:

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:r="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
 <head>
  <title>Hedral's Home Page</title>
  <r:RDF>
   <Person xmlns="http://www.w3.org/2000/10/swap/pim/contact#"
           r:about="http://hedral.example.com/#">
    <fullName>Cat Hedral</fullName>
    <mailbox r:resource="mailto:hedral@damowmow.com"/>
    <personalTitle>Sir</personalTitle>
   </Person>
  </r:RDF>
 </head>
 <body>
  <h1>My home page</h1>
  <p>I like playing with string, I guess. Sister says squirrels are fun
  too so sometimes I follow her to play with them.</p>
 </body>
</html>

This isn't possible in the HTML serialization, however.

3.2.5.1.2 Flow content

Status: Last call for comments

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.

3.2.5.1.3 Sectioning content

Status: Last call for comments

Sectioning content is content that defines the scope of headings and footers.

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

There are also certain elements that are sectioning roots. These are distinct from sectioning content, but they can also have an outline.

3.2.5.1.4 Heading content

Status: Last call for comments

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

3.2.5.1.5 Phrasing content

Status: Last call for comments

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

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

Most elements that are categorized as phrasing content can only contain elements that are themselves categorized as phrasing content, not any flow content.

Text, in the context of content models, means text nodes. Text is sometimes used as a content model on its own, but is also phrasing content, and can be inter-element whitespace (if the text nodes are empty or contain just space characters).

3.2.5.1.6 Embedded content

Status: Last call for comments

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

Elements that are from namespaces other than the HTML namespace and that convey content but not metadata, are embedded content for the purposes of the content models defined in this specification. (For example, MathML, or SVG.)

Some embedded content elements can have fallback content: content that is to be used when the external resource cannot be used (e.g. because it is of an unsupported format). The element definitions state what the fallback is, if any.

3.2.5.1.7 Interactive content

Status: Last call for comments

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

Certain elements in HTML have an activation behavior, which means that the user can activate them. This triggers a sequence of events dependent on the activation mechanism, and normally culminating in a click event followed by a DOMActivate event, as described below.

The user agent should allow the user to manually trigger elements that have an activation behavior, for instance using keyboard or voice input, or through mouse clicks. When the user triggers an element with a defined activation behavior in a manner other than clicking it, the default action of the interaction event must be to run synthetic click activation steps on the element.

When a user agent is to run synthetic click activation steps on an element, the user agent must run pre-click activation steps on the element, then fire a click event at the element. The default action of this click event must be to run post-click activation steps on the element. If the event is canceled, the user agent must run canceled activation steps on the element instead.

Given an element target, the nearest activatable element is the element returned by the following algorithm:

  1. If target has a defined activation behavior, then return target and abort these steps.

  2. If target has a parent element, then set target to that parent element and return to the first step.

  3. Otherwise, there is no nearest activatable element.

When a pointing device is clicked, the user agent must run these steps:

  1. Let e be the nearest activatable element of the element designated by the user, if any.

  2. If there is an element e, run pre-click activation steps on it.

  3. Dispatch the required click event.

    If there is an element e, then the default action of the click event must be to run post-click activation steps on element e.

    If there is an element e but the event is canceled, the user agent must run canceled activation steps on element e.

The above doesn't happen for arbitrary synthetic events dispatched by author script. However, the click() method can be used to make it happen programmatically.

When a user agent is to run pre-click activation steps on an element, it must run the pre-click activation steps defined for that element, if any.

When a user agent is to run post-click activation steps on an element, the user agent must fire a simple event named DOMActivate that is cancelable at that element. The default action of this event must be to run final activation steps on that element. If the event is canceled, the user agent must run canceled activation steps on the element instead.

When a user agent is to run canceled activation steps on an element, it must run the canceled activation steps defined for that element, if any.

When a user agent is to run final activation steps on an element, it must run the activation behavior defined for that element. Activation behaviors can refer to the click and DOMActivate events that were fired by the steps above leading up to this point.

3.2.5.2 Transparent content models

Status: Last call for comments

Some elements are described as transparent; they have "transparent" in the description of their content model.

When a content model includes a part that is "transparent", those parts must not contain content that would not be conformant if all transparent elements in the tree were replaced, in their parent element, by the children in the "transparent" part of their content model, retaining order.

Consider the following markup fragment:

<p>Hello <a href="world.html"><em>wonderful</em> world</a>!</p>

Its DOM looks like the following:

The content model of the a element is transparent. To see if its contents are conforming, therefore, the element is replaced by its contents:

Since that is conforming, the contents of the a are conforming in the original fragment.

When a transparent element has no parent, then the part of its content model that is "transparent" must instead be treated as accepting any flow content.

3.2.5.3 Paragraphs

Status: Last call for comments

The term paragraph as defined in this section is distinct from (though related to) the p element defined later. The paragraph concept defined here is used to describe how to interpret documents.

A paragraph is typically a run of phrasing content that forms 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.

In the following example, there are two paragraphs in a section. There is also a heading, which contains phrasing content that is not a paragraph. Note how the comments and inter-element whitespace do not form paragraphs.

<section>
  <h1>Example of paragraphs</h1>
  This is the <em>first</em> paragraph in this example.
  <p>This is the second.</p>
  <!-- This is not a paragraph. -->
</section>

Paragraphs in flow content are defined relative to what the document looks like without the a, ins, del, and map elements complicating matters, since those elements, with their hybrid content models, can straddle paragraph boundaries, as shown in the first two examples below.

Generally, having elements straddle paragraph boundaries is best avoided. Maintaining such markup can be difficult.

The following example takes the markup from the earlier example and puts ins and del elements around some of the markup to show that the text was changed (though in this case, the changes admittedly don't make much sense). Notice how this example has exactly the same paragraphs as the previous one, despite the ins and del elements — the ins element straddles the heading and the first paragraph, and the del element straddles the boundary between the two paragraphs.

<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>

Let view be a view of the DOM that replaces all a, ins, del, and map elements in the document with their contents. Then, in view, for each run of sibling phrasing content nodes uninterrupted by other types of content, in an element that accepts content other than phrasing content as well as phrasing content, let first be the first node of the run, and let last be the last node of the run. For each such run that consists of at least one node that is neither embedded content nor inter-element whitespace, a paragraph exists in the original DOM from immediately before first to immediately after last. (Paragraphs can thus span across a, ins, del, and map elements.)

Conformance checkers may warn authors of cases where they have paragraphs that overlap each other (this can happen with object, video, audio, and canvas elements, and indirectly through elements in other namespaces that allow HTML to be further embedded therein, like svg or math).

A paragraph is also formed explicitly by p elements.

The p element can be used to wrap individual paragraphs when there would otherwise not be any content other than phrasing content to separate the paragraphs from each other.

In the following example, the link spans half of the first paragraph, all of the heading separating the two paragraphs, and half of the second paragraph. It straddles the paragraphs and the heading.

<aside>
 Welcome!
 <a href="about.html">
  This is home of...
  <h1>The Falcons!</h1>
  The Lockheed Martin multirole jet fighter aircraft!
 </a>
 This page discusses the F-16 Fighting Falcon's innermost secrets.
</aside>

Here is another way of marking this up, this time showing the paragraphs explicitly, and splitting the one link element into three:

<aside>
 <p>Welcome! <a href="about.html">This is home of...</a></p>
 <h1><a href="about.html">The Falcons!</a></h1>
 <p><a href="about.html">The Lockheed Martin multirole jet
 fighter aircraft!</a> This page discusses the F-16 Fighting
 Falcon's innermost secrets.</p>
</aside>

It is possible for paragraphs to overlap when using certain elements that define fallback content. For example, in the following section:

<section>
 <h1>My Cats</h1>
 You can play with my cat simulator.
 <object data="cats.sim">
  To see the cat simulator, use one of the following links:
  <ul>
   <li><a href="cats.sim">Download simulator file</a>
   <li><a href="http://sims.example.com/watch?v=LYds5xY4INU">Use online simulator</a>
  </ul>
  Alternatively, upgrade to the Mellblom Browser.
 </object>
 I'm quite proud of it.
</section>

There are five paragraphs:

  1. The paragraph that says "You can play with my cat simulator. object I'm quite proud of it.", where object is the object element.
  2. The paragraph that says "To see the cat simulator, use one of the following links:".
  3. The paragraph that says "Download simulator file".
  4. The paragraph that says "Use online simulator".
  5. The paragraph that says "Alternatively, upgrade to the Mellblom Browser.".

The first paragraph is overlapped by the other four. A user agent that supports the "cats.sim" resource will only show the first one, but a user agent that shows the fallback will confusingly show the first sentence of the first paragraph as if it was in the same paragraph as the second one, and will show the last paragraph as if it was at the start of the second sentence of the first paragraph.

To avoid this confusion, explicit p elements can be used.

3.2.6 Annotations for assistive technology products (ARIA)

Authors may use the ARIA role and aria-* attributes on HTML elements, in accordance with the requirements described in the ARIA specifications, except where these conflict with the strong native semantics described below. These exceptions are intended to prevent authors from making assistive technology products report nonsensical states that do not represent the actual state of the document. [ARIA]

User agents are required to implement ARIA semantics on all HTML elements, as defined in the ARIA specifications. The implicit ARIA semantics defined below must be recognized by implementations. [ARIAIMPL]

The following table defines the strong native semantics and corresponding implicit ARIA semantics that apply to HTML elements. Each language feature (element or attribute) in a cell in the first column implies the ARIA semantics (role, states, and/or properties) given in the cell in the second column of the same row. Authors must not set the ARIA role and aria-* attributes in a manner that conflicts with the semantics described in the following table. When multiple rows apply to an element, the role from the last row to define a role must be applied, and the states and properties from all the rows must be combined.

Language feature Strong native semantics and implied ARIA semantics
a element that represents a hyperlink link role
area element that represents a hyperlink link role
button element button role
datalist element listbox role, with the aria-multiselectable property set to "false"
h1 element that does not have an hgroup ancestor heading role, with the aria-level property set to the element's outline depth
h2 element that does not have an hgroup ancestor heading role, with the aria-level property set to the element's outline depth
h3 element that does not have an hgroup ancestor heading role, with the aria-level property set to the element's outline depth
h4 element that does not have an hgroup ancestor heading role, with the aria-level property set to the element's outline depth
h5 element that does not have an hgroup ancestor heading role, with the aria-level property set to the element's outline depth
h6 element that does not have an hgroup ancestor heading role, with the aria-level property set to the element's outline depth
hgroup element heading role, with the aria-level property set to the element's outline depth
hr element separator role
img element whose alt attribute's value is empty presentation role
input element with a type attribute in the Button state button role
input element with a type attribute in the Checkbox state checkbox role, with the aria-checked state set to "mixed" if the element's indeterminate IDL attribute is true, or "true" if the element's checkedness is true, or "false" otherwise
input element with a type attribute in the Color state No role
input element with a type attribute in the Date state No role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Date and Time state No role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Local Date and Time state No role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the E-mail state with no suggestions source element textbox role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the File Upload state button role
input element with a type attribute in the Hidden state No role
input element with a type attribute in the Image Button state button role
input element with a type attribute in the Month state No role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Number state spinbutton role, with the aria-readonly state set to "true" if the element has a readonly attribute, the aria-valuemax property set to the element's maximum, the aria-valuemin property set to the element's minimum, and, if the result of applying the rules for parsing floating point number values to the element's value is a number, with the aria-valuenow property set to that number
input element with a type attribute in the Password state textbox role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Radio Button state radio role, with the aria-checked state set to "true" if the element's checkedness is true, or "false" otherwise
input element with a type attribute in the Range state slider role, with the aria-valuemax property set to the element's maximum, the aria-valuemin property set to the element's minimum, and the aria-valuenow property set to the result of applying the rules for parsing floating point number values to the element's value, if that that results in a number, or the default value otherwise
input element with a type attribute in the Reset Button state button role
input element with a type attribute in the Search state with no suggestions source element textbox role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Submit Button state button role
input element with a type attribute in the Telephone state with no suggestions source element textbox role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Text state with no suggestions source element textbox role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Text, Search, Telephone, URL, or E-mail states with a suggestions source element combobox role, with the aria-owns property set to the same value as the list attribute, and the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Time state No role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the URL state with no suggestions source element textbox role, with the aria-readonly state set to "true" if the element has a readonly attribute
input element with a type attribute in the Week state No role, with the aria-readonly state set to "true" if the element has a readonly attribute
link element that represents a hyperlink link role
menu element with a type attribute in the context menu state No role
menu element with a type attribute in the list state menu role
menu element with a type attribute in the toolbar state toolbar role
nav element navigation role
option element that is in a list of options or that represents a suggestion in a datalist element option role, with the aria-selected state set to "true" if the element's selectedness is true, or "false" otherwise.
progress element progressbar role, with, if the progress bar is determinate, the aria-valuemax property set to the maximum value of the progress bar, the aria-valuemin property set to zero, and the aria-valuenow property set to the current value of the progress bar
select element with a multiple attribute listbox role, with the aria-multiselectable property set to "true"
select element with no multiple attribute listbox role, with the aria-multiselectable property set to "false"
td element gridcell role, with the aria-labelledby property set to the value of the headers attribute, if any
textarea element textbox role, with the aria-multiline property set to "true", and the aria-readonly state set to "true" if the element has a readonly attribute
th element that is neither a column header nor a row header gridcell role, with the aria-labelledby property set to the value of the headers attribute, if any
th element that is a column header columnheader role, with the aria-labelledby property set to the value of the headers attribute, if any
th element that is a row header rowheader role, with the aria-labelledby property set to the value of the headers attribute, if any
tr element row role
An element that defines a command, whose Type facet is "checkbox", and that is a descendant of a menu element whose type attribute in the list state menuitemcheckbox role, with the aria-checked state set to "true" if the command's Checked State facet is true, and "false" otherwise
An element that defines a command, whose Type facet is "command", and that is a descendant of a menu element whose type attribute in the list state menuitem role
An element that defines a command, whose Type facet is "radio", and that is a descendant of a menu element whose type attribute in the list state menuitemradio role, with the aria-checked state set to "true" if the command's Checked State facet is true, and "false" otherwise
Elements that are disabled The aria-disabled state set to "true"
Elements that are required The aria-required state set to "true"

Some HTML elements have native semantics that can be overridden. The following table lists these elements and their implicit ARIA semantics, along with the restrictions that apply to those elements. Each language feature (element or attribute) in a cell in the first column implies, unless otherwise overriden, the ARIA semantic (role, state, or property) given in the cell in the second column of the same row, but this semantic may be overridden under the conditions listed in the cell in the third column of that row.

Language feature Default implied ARIA semantic Restrictions
address element No role If specified, role must be contentinfo (ARIA restricts usage of this role to one per page)
article element article role Role must be either article, document, application, or main (ARIA restricts usage of this role to one per page)
aside element note role Role must be either note, complementary, or search
footer element No role If specified, role must be contentinfo (ARIA restricts usage of this role to one per page)
header element No role If specified, role must be banner (ARIA restricts usage of this role to one per page)
li element whose parent is an ol or ul element listitem role Role must be either listitem or treeitem
ol element list role Role must be either list, tree, or directory
output element status role No restrictions
section element region role Role must be either region, document, application, contentinfo (ARIA restricts usage of this role to one per page), main (ARIA restricts usage of this role to one per page), search, alert, dialog, alertdialog, status, or log
table element grid role Role must be either grid or treegrid
ul element list role Role must be either list or tree, or directory
The body element document role Role must be either document or application

User agents may apply different defaults than those described in this section in order to expose the semantics of HTML elements in a manner more fine-grained than possible with the above definitions.

Conformance checkers are encouraged to phrase errors such that authors are encouraged to use more appropriate elements rather than remove accessibility annotations. For example, if an a element is marked as having the button role, a conformance checker could say "Either a button element or an input element is required when using the button role" rather than "The button role cannot be used with a elements".

3.3 APIs in HTML documents

Status: Last call for comments

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

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

Element.tagName and Node.nodeName

These attributes must return element names converted to ASCII uppercase, regardless of the case with which they were created.

Document.createElement()

The canonical form of HTML markup is all-lowercase; thus, this method will lowercase the argument before creating the requisite element. Also, the element created must be in the HTML namespace.

This doesn't apply to Document.createElementNS(). Thus, it is possible, by passing this last method a tag name in the wrong case, to create an element that appears to have the same tag name as that of an element defined in this specification when its tagName attribute is examined, but that doesn't support the corresponding interfaces. The "real" element name (unaffected by case conversions) can be obtained from the localName attribute.

Element.setAttribute()
Element.setAttributeNode()

Attribute names are converted to ASCII lowercase.

Specifically: when an attribute is set on an HTML element using Element.setAttribute(), the name argument must be converted to ASCII lowercase before the element is affected; and when an Attr node is set on an HTML element using Element.setAttributeNode(), it must have its name converted to ASCII lowercase before the element is affected.

This doesn't apply to Element.setAttributeNS() and Element.setAttributeNodeNS().

Element.getAttribute()
Element.getAttributeNode()

Attribute names are converted to ASCII lowercase.

Specifically: When the Element.getAttribute() method or the Element.getAttributeNode() method is invoked on an HTML element, the name argument must be converted to ASCII lowercase before the element's attributes are examined.

This doesn't apply to Element.getAttributeNS() and Element.getAttributeNodeNS().

Document.getElementsByTagName()
Element.getElementsByTagName()

HTML elements match by lower-casing the argument before comparison, elements from other namespaces are treated as in XML (case-sensitively).

Specifically, these methods (but not their namespaced counterparts) must compare the given argument in a case-sensitive manner, but when looking at HTML elements, the argument must first be converted to ASCII lowercase.

Thus, in an HTML document with nodes in multiple namespaces, these methods will effectively be both case-sensitive and case-insensitive at the same time.

3.4 Interactions with XPath and XSLT

Status: Last call for comments

Implementations of XPath 1.0 that operate on HTML documents parsed or created in the manners described in this specification (e.g. as part of the document.evaluate() API) must act as if the following edit was applied to the XPath 1.0 specification.

First, remove this paragraph:

A QName in the node test is expanded into an expanded-name using the namespace declarations from the expression context. This is the same way expansion is done for element type names in start and end-tags except that the default namespace declared with xmlns is not used: if the QName does not have a prefix, then the namespace URI is null (this is the same way attribute names are expanded). It is an error if the QName has a prefix for which there is no namespace declaration in the expression context.

Then, insert in its place the following:

A QName in the node test is expanded into an expanded-name using the namespace declarations from the expression context. If the QName has a prefix, then there must be a namespace declaration for this prefix in the expression context, and the corresponding namespace URI is the one that is associated with this prefix. It is an error if the QName has a prefix for which there is no namespace declaration in the expression context.

If the QName has no prefix and the principal node type of the axis is element, then the default element namespace is used. Otherwise if the QName has no prefix, the namespace URI is null. The default element namespace is a member of the context for the XPath expression. The value of the default element namespace when executing an XPath expression through the DOM3 XPath API is determined in the following way:

  1. If the context node is from an HTML DOM, the default element namespace is "http://www.w3.org/1999/xhtml".
  2. Otherwise, the default element namespace URI is null.

This is equivalent to adding the default element namespace feature of XPath 2.0 to XPath 1.0, and using the HTML namespace as the default element namespace for HTML documents. It is motivated by the desire to have implementations be compatible with legacy HTML content while still supporting the changes that this specification introduces to HTML regarding the namespace used for HTML elements, and by the desire to use XPath 1.0 rather than XPath 2.0.

This change is a willful violation of the XPath 1.0 specification, motivated by desire to have implementations be compatible with legacy content while still supporting the changes that this specification introduces to HTML regarding which namespace is used for HTML elements. [XPATH10]


XSLT 1.0 processors outputting to a DOM when the output method is "html" (either explicitly or via the defaulting rule in XSLT 1.0) are affected as follows:

If the transformation program outputs an element in no namespace, the processor must, prior to constructing the corresponding DOM element node, change the namespace of the element to the HTML namespace, ASCII-lowercase the element's local name, and ASCII-lowercase the names of any non-namespaced attributes on the element.

This requirement is a willful violation of the XSLT 1.0 specification, required because this specification changes the namespaces and case-sensitivity rules of HTML in a manner that would otherwise be incompatible with DOM-based XSLT transformations. (Processors that serialize the output are unaffected.) [XSLT10]

3.5 Dynamic markup insertion

Status: Last call for comments

APIs for dynamically inserting markup into the document interact with the parser, and thus their behavior varies depending on whether they are used with HTML documents (and the HTML parser) or XHTML in XML documents (and the XML parser).

3.5.1 Opening the input stream

Status: Last call for comments

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

document = document . open( [ type [, replace ] ] )

Causes the Document to be replaced in-place, as if it was a new Document object, but reusing the previous object, which is then returned.

If the type argument is omitted or has the value "text/html", then the resulting Document has an HTML parser associated with it, which can be given data to parse using document.write(). Otherwise, all content passed to document.write() will be parsed as plain text.

If the replace argument is present and has the value "replace", the existing entries in the session history for the Document object are removed.

The method has no effect if the Document is still being parsed.

Throws an INVALID_STATE_ERR exception if the Document is an XML document.

window = document . open( url, name, features [, replace ] )

Works like the window.open() method.

When called with two or fewer arguments, the method must act as follows:

  1. If the Document object is not flagged as an HTML document, throw an INVALID_STATE_ERR exception and abort these steps.
  2. Let type be the value of the first argument, if there is one, or "text/html" otherwise.

  3. Let replace be true if there is a second argument and it is an ASCII case-insensitive match for the value "replace", and false otherwise.

  4. 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.

  5. Release the storage mutex.

  6. Prompt to unload the Document object. If the user refused to allow the document to be unloaded, then these steps must be aborted.

  7. Unload the Document object, with the recycle parameter set to true.

  8. If the document has an active parser, then abort that parser.

  9. Unregister all event listeners registered on the Document node and its descendants.

  10. Remove any tasks associated with the Document in any task source.

  11. Remove all child nodes of the document, without firing any mutation events.

  12. Replace the Document's singleton objects with new instances of those objects. (This includes in particular the Window, Location, History, ApplicationCache, UndoManager, Navigator, and Selection objects, the various BarProp objects, the two Storage objects, and the various HTMLCollection objects. It also includes all the Web IDL prototypes in the JavaScript binding, including the Document object's prototype.)

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

  14. Change the document's address to the entry script's document's address.

  15. Create a new HTML parser and associate it with the document. This is a script-created parser (meaning that it can be closed by the document.open() and document.close() methods, and that the tokenizer will wait for an explicit call to document.close() before emitting an end-of-file token). The encoding confidence is irrelevant.

  16. If the type string contains a U+003B SEMICOLON character (;), remove the first such character and all characters from it up to the end of the string.

    Strip all leading and trailing space characters from type.

    If type is not now an ASCII case-insensitive match for the string "text/html", then act as if the tokenizer had emitted a start tag token with the tag name "pre", then switch the HTML parser's tokenizer to the PLAINTEXT state.

  17. Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.

    This doesn't necessarily have to affect the user agent's user interface.

  18. Remove any tasks queued by the history traversal task source.

  19. Remove any earlier entries that share the same Document.
  20. If replace is false, then add a new entry, just before the last entry, and associate with the new entry 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.)

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

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

When called with three or more arguments, the open() method on the HTMLDocument object must call the open() method on the Window object of the HTMLDocument object, with the same arguments as the original call to the open() method, and return whatever that method returned. If the HTMLDocument object has no Window object, then the method must raise an INVALID_ACCESS_ERR exception.

3.5.2 Closing the input stream

Status: Last call for comments

document . close()

Closes the input stream that was opened by the document.open() method.

Throws an INVALID_STATE_ERR exception if the Document is an XML document.

The close() method must run the following steps:

  1. If the Document object is not flagged as an HTML document, throw an INVALID_STATE_ERR exception and abort these steps.

  2. If there is no script-created parser associated with the document, then abort these steps.

  3. Insert an explicit "EOF" character at the end of the parser's input stream.

  4. If there is a pending parsing-blocking script, then abort these steps.

  5. Run the tokenizer, processing resulting tokens as they are emitted, and stopping when the tokenizer reaches the explicit "EOF" character or spins the event loop.

3.5.3 document.write()

document . write(text...)

Adds the given string(s) to the Document's input stream. If necessary, calls the open() method implicitly first.

This method throws an INVALID_STATE_ERR exception when invoked on XML documents.

Unless called from the body of a script element while the document is being parsed, or called on a script-created document, calling this method will clear the current page first, as if document.open() had been called.

The document.write(...) method must act as follows:

  1. If the method was invoked on an XML document, throw an INVALID_STATE_ERR exception and abort these steps.

  2. If the insertion point is undefined, the open() method must be called (with no arguments) on the document object. If the user refused to allow the document to be unloaded, then these steps must be aborted. Otherwise, the insertion point will point at just before the end of the (empty) input stream.

  3. The string consisting of the concatenation of all the arguments to the method must be inserted into the input stream just before the insertion point.

  4. If there is a pending parsing-blocking script, then the method must now return without further processing of the input stream.

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

    If the document.write() method was called from script executing inline (i.e. executing because the parser parsed a set of script tags), then this is a reentrant invocation of the parser.

  6. Finally, the method must return.

3.5.4 document.writeln()

document . writeln(text...)

Adds the given string(s) to the Document's input stream, followed by a newline character. If necessary, calls the open() method implicitly first.

This method throws an INVALID_STATE_ERR exception when invoked on XML documents.

The document.writeln(...) method, when invoked, must act as if the document.write() method had been invoked with the same argument(s), plus an extra argument consisting of a string containing a single line feed character (U+000A).

3.5.5 innerHTML

Status: Last call for comments

The innerHTML IDL attribute represents the markup of the node's contents.

document . innerHTML [ = value ]

Returns a fragment of HTML or XML that represents the Document.

Can be set, to replace the Document's contents with the result of parsing the given string.

In the case of XML documents, will throw an INVALID_STATE_ERR if the Document cannot be serialized to XML, and a SYNTAX_ERR if the given string is not well-formed.

element . innerHTML [ = value ]

Returns a fragment of HTML or XML that represents the element's contents.

Can be set, to replace the contents of the element with nodes parsed from the given string.

In the case of XML documents, will throw an INVALID_STATE_ERR if the element cannot be serialized to XML, and a SYNTAX_ERR if the given string is not well-formed.

On getting, if the node's document is an HTML document, then the attribute must return the result of running the HTML fragment serialization algorithm on the node; otherwise, the node's document is an XML document, and the attribute must return the result of running the XML fragment serialization algorithm on the node instead (this might raise an exception instead of returning a string).

On setting, the following steps must be run:

  1. If the node's document is an HTML document: Invoke the HTML fragment parsing algorithm.

    If the node's document is an XML document: Invoke the XML fragment parsing algorithm.

    In either case, the algorithm must be invoked with the string being assigned into the innerHTML attribute as the input. If the node is an Element node, then, in addition, that element must be passed as the context element.

    If this raises an exception, then abort these steps.

    Otherwise, let new children be the nodes returned.

  2. If the attribute is being set on a Document node, and that document has an active parser, then abort that parser.

  3. Remove the child nodes of the node whose innerHTML attribute is being set, firing appropriate mutation events.

  4. If the attribute is being set on a Document node, let target document be that Document node. Otherwise, the attribute is being set on an Element node; let target document be the ownerDocument of that Element.

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

  6. Append all the new children nodes to the node whose innerHTML attribute is being set, preserving their order, and firing mutation events as if a DocumentFragment containing the new children had been inserted.

3.5.6 outerHTML

Status: Last call for comments

The outerHTML IDL attribute represents the markup of the element and its contents.

element . outerHTML [ = value ]

Returns a fragment of HTML or XML that represents the element and its contents.

Can be set, to replace the element with nodes parsed from the given string.

In the case of XML documents, will throw an INVALID_STATE_ERR if the element cannot be serialized to XML, and a SYNTAX_ERR if the given string is not well-formed.

Throws a NO_MODIFICATION_ALLOWED_ERR exception if the parent of the element is the Document node.

On getting, if the node's document is an HTML document, then the attribute must return the result of running the HTML fragment serialization algorithm on a fictional node whose only child is the node on which the attribute was invoked; otherwise, the node's document is an XML document, and the attribute must return the result of running the XML fragment serialization algorithm on that fictional node instead (this might raise an exception instead of returning a string).

On setting, the following steps must be run:

  1. Let target be the element whose outerHTML attribute is being set.

  2. If target has no parent node, then abort these steps. There would be no way to obtain a reference to the nodes created even if the remaining steps were run.

  3. If target's parent node is a Document object, throw a NO_MODIFICATION_ALLOWED_ERR exception and abort these steps.

  4. Let parent be target's parent node, unless that is a DocumentFragment node, in which case let parent be an arbitrary body element.

  5. If target's document is an HTML document: Invoke the HTML fragment parsing algorithm.

    If target's document is an XML document: Invoke the XML fragment parsing algorithm.

    In either case, the algorithm must be invoked with the string being assigned into the outerHTML attribute as the input, and parent as the context element.

    If this raises an exception, then abort these steps.

    Otherwise, let new children be the nodes returned.

  6. Set the ownerDocument of all the nodes in new children to target's document.

  7. Remove target from its parent node, firing mutation events as appropriate, and then insert in its place all the new children nodes, preserving their order, and again firing mutation events as if a DocumentFragment containing the new children had been inserted.

3.5.7 insertAdjacentHTML()

element . insertAdjacentHTML(position, text)

Parses the given string text as HTML or XML and inserts the resulting nodes into the tree in the position given by the position argument, as follows:

"beforebegin"
Before the element itself.
"afterbegin"
Just inside the element, before its first child.
"beforeend"
Just inside the element, after its last child.
"afterend"
After the element itself.

Throws a SYNTAX_ERR exception if the arguments have invalid values (e.g., in the case of XML documents, if the given string is not well-formed).

Throws a NO_MODIFICATION_ALLOWED_ERR exception if the given position isn't possible (e.g. inserting elements after the root element of a Document).

The insertAdjacentHTML(position, text) method, when invoked, must run the following algorithm:

  1. Let position and text be the method's first and second arguments, respectively.

  2. Let target be the element on which the method was invoked.

  3. Use the first matching item from this list:

    If position is an ASCII case-insensitive match for the string "beforebegin"
    If position is an ASCII case-insensitive match for the string "afterend"

    If target has no parent node, then abort these steps.

    If target's parent node is a Document object, then throw a NO_MODIFICATION_ALLOWED_ERR exception and abort these steps.

    Otherwise, let context be the parent node of target.

    If position is an ASCII case-insensitive match for the string "afterbegin"
    If position is an ASCII case-insensitive match for the string "beforeend"

    Let context be the same as target.

    Otherwise

    Throw a SYNTAX_ERR exception.

  4. If target's document is an HTML document: Invoke the HTML fragment parsing algorithm.

    If target's document is an XML document: Invoke the XML fragment parsing algorithm.

    In either case, the algorithm must be invoked with text as the input, and the element selected in by the previous step as the context element.

    If this raises an exception, then abort these steps.

    Otherwise, let new children be the nodes returned.

  5. Set the ownerDocument of all the nodes in new children to target's document.

  6. Use the first matching item from this list:

    If position is an ASCII case-insensitive match for the string "beforebegin"

    Insert all the new children nodes immediately before target.

    If position is an ASCII case-insensitive match for the string "afterbegin"

    Insert all the new children nodes before the first child of target, if there is one. If there is no such child, append them all to target.

    If position is an ASCII case-insensitive match for the string "beforeend"

    Append all the new children nodes to target.

    If position is an ASCII case-insensitive match for the string "afterend"

    Insert all the new children nodes immediately after target.

    The new children nodes must be inserted in a manner that preserves their order and fires mutation events as if a DocumentFragment containing the new children had been inserted.

4 The elements of HTML

4.1 The root element

Status: Last call for comments

4.1.1 The html element

Status: Last call for comments

Categories
None.
Contexts in which this element may be used:
As the root element of a document.
Wherever a subdocument fragment is allowed in a compound document.
Content model:
A head element followed by a body element.
Content attributes:
Global attributes
manifest
DOM interface:
interface HTMLHtmlElement : 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 non-empty URL potentially surrounded by spaces.

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

For the purposes of application cache selection, later base elements cannot affect the resolving of relative URLs in manifest attributes, as the attributes are processed before those elements are seen.

The window.applicationCache IDL attribute provides scripted access to the offline application cache mechanism.

The html element in the following example declares that the document's language is English.

<!DOCTYPE html>
<html lang="en">
<head>
<title>Swapping Songs</title>
</head>
<body>
<h1>Swapping Songs</h1>
<p>Tonight I swapped some of the songs I wrote with some friends, who
gave me some of the songs they wrote. I love sharing my music.</p>
</body>
</html>

4.2 Document metadata

Status: Last call for comments

4.2.1 The head element

Status: Last call for comments

Categories
None.
Contexts in which this element may be used:
As the first element in an html element.
Content model:
If the document is an iframe srcdoc document or if title information is available from a higher-level protocol: Zero or more elements of metadata content.
Otherwise: One or more elements of metadata content, of which exactly one is a title element.
Content attributes:
Global attributes
DOM interface:
interface HTMLHeadElement : HTMLElement {};

The head element represents a collection of metadata for the Document.

The collection of metadata in a head element can be large or small. Here is an example of a very short one:

<!doctype html>
<html>
 <head>
  <title>A document with a short head</title>
 </head>
 <body>
 ...

Here is an example of a longer one:

<!DOCTYPE HTML>
<HTML>
 <HEAD>
  <META CHARSET="UTF-8">
  <BASE HREF="http://www.example.com/">
  <TITLE>An application with a long head</TITLE>
  <LINK REL="STYLESHEET" HREF="default.css">
  <LINK REL="STYLESHEET ALTERNATE" HREF="big.css" TITLE="Big Text">
  <SCRIPT SRC="support.js"></SCRIPT>
  <META NAME="APPLICATION-NAME" CONTENT="Long headed application">
 </HEAD>
 <BODY>
 ...

The title element is a required child in most situations, but when a higher-level protocol provides title information, e.g. in the Subject line of an e-mail when HTML is used as an e-mail authoring format, the title element can be omitted.

4.2.2 The title element

Status: Last call for comments

Categories
Metadata content.
Contexts in which this element may be used:
In a head element containing no other title elements.
Content model:
Text.
Content attributes:
Global attributes
DOM interface:
interface HTMLTitleElement : HTMLElement {
           attribute DOMString text;
};

The title element represents the document's title or name. Authors should use titles that identify their documents even when they are used out of context, for example in a user's history or bookmarks, or in search results. The document's title is often different from its first heading, since the first heading does not have to stand alone when taken out of context.

There must be no more than one title element per document.

title . text [ = value ]

Returns the contents of the element, ignoring child nodes that aren't text nodes.

Can be set, to replace the element's children with the given value.

The IDL attribute text must return a concatenation of the contents of all the text nodes that are direct children of the title element (ignoring any other nodes such as comments or elements), in tree order. On setting, it must act the same way as the textContent IDL attribute.

Here are some examples of appropriate titles, contrasted with the top-level headings that might be used on those same pages.

  <title>Introduction to The Mating Rituals of Bees</title>
    ...
  <h1>Introduction</h1>
  <p>This companion guide to the highly successful
  <cite>Introduction to Medieval Bee-Keeping</cite> book is...

The next page might be a part of the same site. Note how the title describes the subject matter unambiguously, while the first heading assumes the reader knows what the context is and therefore won't wonder if the dances are Salsa or Waltz:

  <title>Dances used during bee mating rituals</title>
    ...
  <h1>The Dances</h1>

The string to use as the document's title is given by the document.title IDL attribute. User agents should use the document's title when referring to the document in their user interface.

4.2.3 The base element

Status: Last call for comments

Categories
Metadata content.
Contexts in which this element may be used:
In a head element containing no other base elements.
Content model:
Empty.
Content attributes:
Global attributes
href
target
DOM interface:
interface HTMLBaseElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
};

The base element allows authors to specify the document base URL for the purposes of resolving relative URLs, and the name of the default browsing context for the purposes of following hyperlinks. The element does not represent any content beyond this information.

There must be no more than one base element per document.

A base element must have either an href attribute, a target attribute, or both.

The href content attribute, if specified, must contain a valid URL potentially surrounded by spaces.

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

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

The target attribute, if specified, must contain a valid browsing context name or keyword, which specifies which browsing context is to be used as the default when hyperlinks and forms in the Document cause navigation.

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

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

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

In this example, a base element is used to set the document base URL:

<!DOCTYPE html>
<html>
    <head>
        <title>This is an example for the &lt;base&gt; element</title>
        <base href="http://www.example.com/news/index.html">
    </head>
    <body>
        <p>Visit the <a href="archives.html">archives</a>.</p>
    </body>
</html>

The link in the above example would be a link to "http://www.example.com/news/archives.html".

Status: Last call for comments

Categories
Metadata content.
Contexts in which this element may be used:
Where metadata content is expected.
In a noscript element that is a child of a head element.
Content model:
Empty.
Content attributes:
Global attributes
href
rel
media
hreflang
type
sizes
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLLinkElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString href;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
  [PutForwards=value] readonly attribute DOMSettableTokenList sizes;
};
HTMLLinkElement implements LinkStyle;

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

The destination of the link(s) is given by the href attribute, which must be present and must contain a valid non-empty URL potentially surrounded by spaces. If the href attribute is absent, then the element does not define a link.

A link element must have rel attribute.

The types of link indicated (the relationships) are given by the value of the rel attribute, which, if present, 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 none of the values used are allowed according to the definitions in this specification, then the element does not define a link.

Two categories of links can be created using the link element. Links to external resources are links to resources that are to be used to augment the current document, and hyperlink links are links to other documents. The link types section defines whether a particular link type is an external resource or a hyperlink. One element can create multiple links (of which some might be external resource links and some might be hyperlinks); exactly which and how many links are created depends on the keywords given in the rel attribute. User agents must process the links on a per-link basis, not a per-element basis.

Each link is handled separately. For instance, if there are two link elements with rel="stylesheet", they each count as a separate external resource, and each is affected by its own attributes independently.

The exact behavior for links to external resources depends on the exact relationship, as defined for the relevant link type. Some of the attributes control whether or not the external resource is to be applied (as defined below).

For external resources that are represented in the DOM (for example, style sheets), the DOM representation must be made available even if the resource is not applied. To obtain the resource, the user agent must run the following steps:

  1. If the href attribute's value is the empty string, then abort these steps.

  2. Resolve the URL given by the href attribute, relative to the element.

  3. If the previous step fails, then abort these steps.

  4. Fetch the resulting absolute URL.

User agents may opt to only try to obtain such resources when they are needed, instead of pro-actively fetching all the external resources that are not applied.

The semantics of the protocol used (e.g. HTTP) must be followed when fetching external resources. (For example, redirects will be followed and 404 responses will cause the external resource to not be applied.)

Once the attempts to obtain the resource and its critical subresources are complete, the user agent must, if the loads were successful, queue a task to fire a simple event named load at the link element, or, if the resource or one of its critical subresources failed to completely load for any reason (e.g. DNS error, HTTP 404 response, a connection being prematurely closed, unsupported Content-Type), queue a task to fire a simple event named error at the link element. Non-network errors in processing the resource or its subresources (e.g. CSS parse errors, PNG decoding errors) are not failures for the purposes of this paragraph.

The task source for these tasks is the DOM manipulation task source.

The element must delay the load event of the element's document until all the attempts to obtain the resource and its critical subresources are complete. (Resources that the user agent has not yet attempted to obtain, e.g. because it is waiting for the resource to be needed, do not delay the load event.)


Interactive user agents may 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 could include the following information (obtained from the element's attributes, again as defined below), in some form or another (possibly simplified), for each hyperlink created with each link element in the document:

User agents could 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.

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 when the media attribute's value matches the environment and the other relevant conditions apply, and must not apply it otherwise.

The external resource might have further restrictions defined within that limit its applicability. For example, a CSS style sheet might have some @media blocks. This specification does not override such further restrictions or requirements.

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

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

The type attribute gives the MIME type of the linked resource. It is purely advisory. The value must be a valid MIME type.

For external resource links, the type attribute is used as a hint to user agents so that they can avoid fetching resources they do not support. If the attribute is present, then the user agent must assume that the resource is of the given type (even if that is not a valid MIME type, e.g. the empty string). 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 obtain the resource; if the UA does support the given MIME type for the given link relationship, then the UA should obtain 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 obtain the resource if the type was known and supported, then the user agent should obtain 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.

The stylesheet link type defines rules for processing the resource's Content-Type metadata.

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

If a document contains style sheet links labeled as follows:

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

...then a compliant UA that supported only CSS style sheets would fetch the B and C files, and skip the A file (since text/plain is not the MIME type for CSS style sheets).

For files B and C, it would then check the actual types returned by the server. For those that are sent as text/css, it would apply the styles, but for those labeled as text/plain, or any other type, it would not.

If one of the two files was returned without a Content-Type metadata, or with a syntactically incorrect type like Content-Type: "null", then the default type for stylesheet links would kick in. Since that default type is text/css, the style sheet would nonetheless be applied.

The title attribute gives the title of the link. With one exception, it is purely advisory. The value is text. The exception is for style sheet links, where the title attribute defines alternative style sheet sets.

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

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

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

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

The IDL attribute relList must reflect the rel content attribute.

The IDL 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.

The LinkStyle interface is also implemented by this element; the styling processing model defines how. [CSSOM]

Here, a set of link elements provide some style sheets:

<!-- a persistent style sheet -->
<link rel="stylesheet" href="default.css">

<!-- the preferred alternate style sheet -->
<link rel="stylesheet" href="green.css" title="Green styles">

<!-- some alternate style sheets -->
<link rel="alternate stylesheet" href="contrast.css" title="High contrast">
<link rel="alternate stylesheet" href="big.css" title="Big fonts">
<link rel="alternate stylesheet" href="wide.css" title="Wide screen">

The following example shows how you can specify versions of the page that use alternative formats, are aimed at other languages, and that are intended for other media:

<link rel=alternate href="/en/html" hreflang=en type=text/html title="English HTML">
<link rel=alternate href="/fr/html" hreflang=fr type=text/html title="French HTML">
<link rel=alternate href="/en/html/print" hreflang=en type=text/html media=print title="English HTML (for printing)">
<link rel=alternate href="/fr/html/print" hreflang=fr type=text/html media=print title="French HTML (for printing)">
<link rel=alternate href="/en/pdf" hreflang=en type=application/pdf title="English PDF">
<link rel=alternate href="/fr/pdf" hreflang=fr type=application/pdf title="French PDF">

4.2.5 The meta element

Status: Last call for comments

Categories
Metadata content.
Contexts in which this element may be used:
If the charset attribute is present, or if the element's http-equiv attribute is in the Encoding declaration state: in a head element.
If the http-equiv attribute is present but not in the Encoding declaration state: in a head element.
If the http-equiv attribute is present but not in the Encoding declaration state: in a noscript element that is a child of a head element.
If the name attribute is present: where metadata content is expected.
Content model:
Empty.
Content attributes:
Global attributes
name
http-equiv
content
charset
DOM interface:
interface HTMLMetaElement : HTMLElement {
           attribute DOMString name;
           attribute DOMString httpEquiv;
           attribute DOMString content;
};

The meta element represents various kinds of metadata that cannot be expressed using the title, base, link, style, and script elements.

The meta element can represent document-level metadata with the name attribute, pragma directives with the http-equiv attribute, and the file's character encoding declaration when an HTML document is serialized to string form (e.g. for transmission over the network or for disk storage) with the charset attribute.

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

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

The charset attribute specifies the character encoding used by the document. This is a character encoding declaration. If the attribute is present in an XML document, its value must be an ASCII case-insensitive match for the string "UTF-8" (and the document is therefore forced to use UTF-8 as its encoding).

The charset attribute on the meta element has no effect in XML documents, and is only allowed in order to facilitate migration to and from XHTML.

There must not be more than one meta element with a charset attribute per document.

The content attribute gives the value of the document metadata or pragma directive when the element is used for those purposes. The allowed values depend on the exact context, as described in subsequent sections of this specification.

If a meta element has a name attribute, it sets document metadata. Document metadata is expressed in terms of name/value pairs, the name attribute on the meta element giving the name, and the content attribute on the same element giving the value. The name specifies what aspect of metadata is being set; valid names and the meaning of their values are described in the following sections. If a meta element has no content attribute, then the value part of the metadata name/value pair is the empty string.

The name and content IDL attributes must reflect the respective content attributes of the same name. The IDL attribute httpEquiv must reflect the content attribute http-equiv.

4.2.5.1 Standard metadata names

Status: Last call for comments

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

Names are case-insensitive, and must be compared in an ASCII case-insensitive manner.

application-name

The value must be a short free-form string 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. There must not be more than one meta element with its name attribute set to the value application-name per document. 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.

author

The value must be a free-form string giving the name of one of the page's authors.

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. There must not be more than one meta element with its name attribute set to the value description per document.

generator

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

Here is what a tool called "Frontweaver" could include in its output, in the page's head element, to identify itself as the tool used to generate the page:

<meta name=generator content="Frontweaver 8.2">
keywords

The value must be a set of comma-separated tokens, each of which is a keyword relevant to the page.

This page about typefaces on British motorways uses a meta element to specify some keywords that users might use to look for the page:

<!DOCTYPE HTML>
<html>
 <head>
  <title>Typefaces on UK motorways</title>
  <meta name="keywords" content="british,type face,font,fonts,highway,highways">
 </head>
 <body>
  ...

Many search engines do not consider such keywords, because this feature has historically been used unreliably and even misleadingly as a way to spam search engine results in a way that is not helpful for users.

To obtain the list of keywords that the author has specified as applicable to the page, the user agent must run the following steps:

  1. Let keywords be an empty list.

  2. For each meta element with a name attribute and a content attribute and whose name attribute's value is keywords, run the following substeps:

    1. Split the value of the element's content attribute on commas.

    2. Add the resulting tokens, if any, to keywords.

  3. Remove any duplicates from keywords.

  4. Return keywords. This is the list of keywords that the author has specified as applicable to the page.

User agents should not use this information when there is insufficient confidence in the reliability of the value.

For instance, it would be reasonable for a content management system to use the keyword information of pages within the system to populate the index of a site-specific search engine, but a large-scale content aggregator that used this information would likely find that certain users would try to game its ranking mechanism through the use of inappropriate keywords.

4.2.5.2 Other metadata names

Status: Last call for comments. ISSUE-27 (rel-ownership) blocks progress to Last Call

Extensions to the predefined set of metadata names may be registered in the WHATWG Wiki MetaExtensions page. [WHATWGWIKI]

Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time to add a type. These new names must be specified with the following information:

Keyword

The actual name being defined. The name should not be confusingly similar to any other defined name (e.g. differing only in case).

Brief description

A short non-normative description of what the metadata name's meaning is, including the format the value is required to be in.

Specification
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. Anyone may remove synonyms that are not used in practice; only names that need to be processed as synonyms for compatibility with legacy content are to be registered in this way.

Status

One of the following:

Proposed
The name has not received wide peer review and approval. Someone has proposed it and is, or soon will be, using it.
Ratified
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.
Discontinued
The metadata name has received wide peer review and it has been found wanting. Existing pages are using this metadata name, but new pages should avoid it. The "brief description" and "specification" entries will give details of what authors should use instead, if anything.

If a metadata name is found to be redundant with existing values, it should be removed and listed as a synonym for the existing value.

If a metadata name is registered in the "proposed" state for a period of a month or more without being used or specified, then it may be removed from the registry.

If a metadata name is added with the "proposed" status and found to be redundant with existing values, it should be removed and listed as a synonym for the existing value. If a metadata name is added with the "proposed" status and found to be harmful, then it should be changed to "discontinued" status.

Anyone can change the status at any time, but should only do so in accordance with the definitions above.

Conformance checkers must use the information given on the WHATWG Wiki MetaExtensions page to establish if a value is allowed or not: values defined in this specification or marked as "proposed" or "ratified" must be accepted, whereas values marked as "discontinued" or not listed in either this specification or on the aforementioned page must be rejected as invalid. Conformance checkers may cache this information (e.g. for performance reasons or to avoid the use of unreliable network connectivity).

When an author uses a new metadata name 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 "proposed" status.

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

Status: Last call for comments

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.

State Keywords Notes
Content Language content-language Conformance checkers will include a warning
Encoding declaration content-type
Default style default-style
Refresh refresh

When a meta element is inserted into the document, if its http-equiv attribute is present and represents one of the above states, then the user agent must run the algorithm appropriate for that state, as described in the following list:

Content language state (http-equiv="content-language")

This pragma sets the pragma-set default language. Until the pragma is successfully processed, there is no pragma-set default language.

Conformance checkers will include a warning if this pragma is used. Authors are encouraged to use the lang attribute instead.

  1. If another meta element with an http-equiv attribute in the Content Language state has already been successfully processed (i.e. when it was inserted the user agent processed it and reached the last step of this list of steps), then abort these steps.

  2. If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.

  3. If the element's content attribute contains a U+002C COMMA character (,) then abort these steps.

  4. Let input be the value of the element's content attribute.

  5. Let position point at the first character of input.

  6. Skip whitespace.

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

  8. Let the pragma-set default language be the string that resulted from the previous step.

For meta elements with an http-equiv attribute in the Content Language state, the content attribute must have a value consisting of a valid BCP 47 language tag. [BCP47]

This pragma is not exactly equivalent to the HTTP Content-Language header, for instance it only supports one language. [HTTP]

Encoding declaration state (http-equiv="content-type")

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

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

If the document contains a meta element with an http-equiv attribute in the Encoding declaration state, then the document must not contain a meta element with the charset attribute present.

The Encoding declaration state may be used in HTML documents, but elements with an http-equiv attribute in that state must not be used in XML documents.

Default style state (http-equiv="default-style")

This pragma sets the name of the default alternative style sheet set.

  1. If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.

  2. Set the preferred style sheet set to the value of the element's content attribute. [CSSOM]

Refresh state (http-equiv="refresh")

This pragma acts as timed redirect.

  1. If another meta element with an http-equiv attribute 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 (0) to U+0039 DIGIT NINE (9), 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 (0) to U+0039 DIGIT NINE (9) 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 a U+0055 LATIN CAPITAL LETTER U character (U) or a U+0075 LATIN SMALL LETTER U character (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 a U+0052 LATIN CAPITAL LETTER R character (R) or a U+0072 LATIN SMALL LETTER R character (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 s U+004C LATIN CAPITAL LETTER L character (L) or a U+006C LATIN SMALL LETTER L character (l), then advance position to the next character. Otherwise, jump to the last step.

  15. Skip whitespace.

  16. If the character in input pointed to by position is a U+003D EQUALS SIGN ("="), then advance position to the next character. Otherwise, jump to the last step.

  17. Skip whitespace.

  18. If the character in input pointed to by position is either a U+0027 APOSTROPHE character (') or U+0022 QUOTATION MARK character ("), then let quote be that character, and advance position to the next character. Otherwise, let quote be the empty string.

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

  20. If quote is not the empty string, and there is a character in url equal to quote, then truncate url at that character, so that it and all subsequent characters are removed.

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

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

  23. Resolve the url value to an absolute URL, relative to the meta element. If this fails, abort these steps.

  24. Perform one or more of the following steps:

    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 with an http-equiv attribute in the Refresh state, the content attribute must have a value consisting either of:

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

A news organization's front page could include the following markup in the page's head element, to ensure that the page automatically reloads from the server every five minutes:

<meta http-equiv="Refresh" content="300">

A sequence of pages could be used as an automated slide show by making each page refresh to the next page in the sequence, using markup such as the following:

<meta http-equiv="Refresh" content="20; URL=page4.html">

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

4.2.5.4 Other pragma directives

Status: Last call for comments

Extensions to the predefined set of pragma directives may, under certain conditions, be registered in the WHATWG Wiki PragmaExtensions page. [WHATWGWIKI]

Such extensions must use a name that is identical to an HTTP header registered in the Permanent Message Header Field Registry, and must have behavior identical to that described for the HTTP header. [IANAPERMHEADERS]

Pragma directives corresponding to headers describing metadata, or not requiring specific user agent processing, must not be registered; instead, use metadata names. Pragma directives corresponding to headers that affect the HTTP processing model (e.g. caching) must not be registered, as they would result in HTTP-level behavior being different for user agents that implement HTML than for user agents that do not.

Anyone is free to edit the WHATWG Wiki PragmaExtensions page at any time to add a pragma directive satisfying these conditions. Such registrations must specify the following information:

Keyword

The actual name being defined. The name must match a previously-registered HTTP name with the same requirements.

Brief description

A short non-normative description of the purpose of the pragma directive.

Specification
A link to the specification defining the corresponding HTTP header.

Conformance checkers must use the information given on the WHATWG Wiki PragmaExtensions page to establish if a value is allowed or not: values defined in this specification or listed on the aforementioned page must be accepted, whereas values not listed in either this specification or on the aforementioned page must be rejected as invalid. Conformance checkers may cache this information (e.g. for performance reasons or to avoid the use of unreliable network connectivity).

4.2.5.5 Specifying the document's character encoding

Status: Last call for comments

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

The following restrictions apply to character encoding declarations:

If an HTML document does not start with a BOM, and if its encoding is not explicitly given by Content-Type metadata, and the document is not an iframe srcdoc document, 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 with an http-equiv attribute in the Encoding declaration state.

If the document is an iframe srcdoc document, the document must not have a character encoding declaration. (In this case, the source is already decoded, since it is part of the document that contained the iframe.)

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

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

Authoring tools should default to using UTF-8 for newly-created documents.

Encodings in which a series of bytes in the range 0x20 to 0x7E can encode characters other than the corresponding characters in the range U+0020 to U+007E represent a potential security vulnerability: a user agent that does not support the encoding (or does not support the label used to declare the encoding, or does not use the same mechanism to detect the encoding of unlabelled content as another user agent) might end up interpreting technically benign plain text content as HTML tags and JavaScript. For example, this applies to encodings in which the bytes corresponding to "<script>" in ASCII can encode a different string. Authors should not use such encodings, which are known to include JIS_C6226-1983, JIS_X0212-1990, HZ-GB-2312, JOHAB (Windows code page 1361), encodings based on ISO-2022, and encodings based on EBCDIC. Furthermore, authors must not use the CESU-8, UTF-7, BOCU-1 and SCSU encodings, which also fall into this category, because these encodings were never intended for use for Web content. [RFC1345] [RFC1842] [RFC1468] [RFC2237] [RFC1554] [RFC1922] [RFC1557] [CESU8] [UTF7] [BOCU1] [SCSU]

Authors should not use UTF-32, as the encoding detection algorithms described in this specification intentionally do not distinguish it from UTF-16. [UNICODE]

Using non-UTF-8 encodings can have unexpected results on form submission and URL encodings, which use the document's character encoding by default.

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

In HTML, to declare that the character encoding is UTF-8, the author could include the following markup near the top of the document (in the head element):

<meta charset="utf-8">

In XML, the XML declaration would be used instead, at the very top of the markup:

<?xml version="1.0" encoding="utf-8"?>

4.2.6 The style element

Status: Last call for comments

Categories
Metadata content.
If the scoped attribute is present: flow content.
Contexts in which this element may be used:
If the scoped attribute is absent: where metadata content is expected.
If the scoped attribute is absent: in a noscript element that is a child of a head element.
If the scoped attribute is present: where flow content is expected, but before any other flow content other than other style elements and inter-element whitespace.
Content model:
Depends on the value of the type attribute, but must match requirements described in prose below.
Content attributes:
Global attributes
media
type
scoped
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLStyleElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString media;
           attribute DOMString type;
           attribute boolean scoped;
};
HTMLStyleElement implements LinkStyle;

The style element allows authors to embed style information in their documents. The style element is one of several inputs to the styling processing model. The element does not represent content for the user.

The type attribute gives the styling language. If the attribute is present, its value must be a valid MIME type that designates a styling language. The charset parameter must not be specified. The default, which is used if the attribute is absent, is "text/css". [RFC2318]

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 charset parameter must be treated as an unknown parameter for the purpose of comparing MIME types here.

The media attribute says which media the styles apply to. The value must be a valid media query. The user agent must apply the styles when the media attribute's value matches the environment and the other relevant conditions apply, and must not apply them otherwise.

The styles might be further limited in scope, e.g. in CSS with the use of @media blocks. This specification does not override such further restrictions or requirements.

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

The scoped attribute is a boolean attribute. If set, it indicates that the styles are intended just for the subtree rooted at the style element's parent element, as opposed to the whole Document.

If the scoped attribute is present, then the user agent must apply the specified style information only to the style element's parent element (if any), and that element's child nodes. Otherwise, the specified styles must, if applied, be applied to the entire document.

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

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.

The textContent of a style element must match the style production in the following ABNF, the character set for which is Unicode. [ABNF]

style         = no-c-start *( c-start no-c-end c-end no-c-start )
no-c-start    = <any string that doesn't contain a substring that matches c-start >
c-start       = "<!--"
no-c-end      = <any string that doesn't contain a substring that matches c-end >
c-end         = "-->"

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

All URLs found by the styling language's processor must be resolved, relative to the element (or as defined by the styling language), when the processor is invoked.

Once the attempts to obtain the style sheet's critical subresources, if any, are complete, or, if the style sheet has no critical subresources, once the style sheet has been parsed and processed, the user agent must, if the loads were successful or there were none, queue a task to fire a simple event named load at the style element, or, if one of the style sheet's critical subresources failed to completely load for any reason (e.g. DNS error, HTTP 404 response, a connection being prematurely closed, unsupported Content-Type), queue a task to fire a simple event named error at the style element. Non-network errors in processing the style sheet or its subresources (e.g. CSS parse errors, PNG decoding errors) are not failures for the purposes of this paragraph.

The task source for these tasks is the DOM manipulation task source.

The element must delay the load event of the element's document until all the attempts to obtain the style sheet's critical subresources, if any, are complete.

This specification does not specify a style system, but CSS is expected to be supported by most Web browsers. [CSS]

The media, type and scoped IDL attributes must reflect the respective content attributes of the same name.

The disabled IDL attribute behaves as defined for the alternative style sheets DOM.

The LinkStyle interface is also implemented by this element; the styling processing model defines how. [CSSOM]

The following document has its emphasis styled as bright red text rather than italics text, while leaving titles of works and Latin words in their default italics. It shows how using appropriate elements enables easier restyling of documents.

<!DOCTYPE html>
<html lang="en-US">
 <head>
  <title>My favorite book</title>
  <style>
   body { color: black; background: white; }
   em { font-style: normal; color: red; }
  </style>
 </head>
 <body>
  <p>My <em>favorite</em> book of all time has <em>got</em> to be
  <cite>A Cat's Life</cite>. It is a book by P. Rahmel that talks
  about the <i lang="la">Felis Catus</i> in modern human society.</p>
 </body>
</html>

4.2.7 Styling

Status: Last call for comments

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

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

For style elements, if the user agent does not support the specified styling language, then the sheet attribute of the element's LinkStyle interface must return null. Similarly, link elements that do not represent external resource links that contribute to the styling processing model (i.e. that do not have a stylesheet keyword in their rel attribute), and link elements whose specified resource has not yet been fetched, or is not in a supported styling language, must have their LinkStyle interface's sheet attribute return null.

Otherwise, the LinkStyle interface's sheet attribute must return a StyleSheet object with the following properties: [CSSOM]

The style sheet type

The style sheet 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 style sheet location

For link elements, the location must be the result of resolving the URL given by the element's href content attribute, relative to the element, or the empty string if that fails. For style elements, there is no location.

The style sheet media

The media must be the same as the value of the element's media content attribute, or the empty string, if the attribute is omitted.

The style sheet title

The title must be the same as the value of the element's title content attribute, if the attribute is present and has a non-empty value. If the attribute is absent or its value is the empty string, then the style sheet does not have a title (it is the empty string). The title is used for defining alternative style sheet sets.

The style sheet alternate flag

For link elements, true if the link is an alternative stylesheet. In all other cases, false.

The same object must be returned each time.

The disabled IDL 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.

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


Style sheets, whether added by a link element, a style element, an <?xml-stylesheet> PI, an HTTP Link: header, or some other mechanism, have a style sheet ready flag, which is initially unset.

When a style sheet is ready to be applied, its style sheet ready flag must be set. If the style sheet referenced no other resources (e.g. it was an internal style sheet given by a style element with no @import rules), then the style rules must be synchronously made available to script; otherwise, the style rules must only be made available to script once the event loop reaches its "update the rendering" step.

A style sheet in the context of the Document of an HTML parser or XML parser is said to be a style sheet blocking scripts if the element was created by that Document's parser, and the element is either a style element or a link element that was an external resource link that contributes to the styling processing model when the element was created by the parser, and the element's style sheet was enabled when the element was created by the parser, and the element's style sheet ready flag is not yet set, and, the last time the event loop reached step 1, the element was in that Document, and the user agent hasn't given up on that particular style sheet yet. A user agent may give up on a style sheet at any time.

4.3 Scripting

Status: Last call for comments

Scripts allow authors to add interactivity to their documents.

Authors are encouraged to use declarative alternatives to scripting where possible, as declarative mechanisms are often more maintainable, and many users disable scripting.

For example, instead of using script to show or hide a section to show more details, the details element could be used.

Authors are also encouraged to make their applications degrade gracefully in the absence of scripting support.

For example, if an author provides a link in a table header to dynamically resort the table, the link could also be made to function without scripts by requesting the sorted table from the server.

4.3.1 The script element

Status: Last call for comments

Categories
Metadata content.
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where metadata content is expected.
Where phrasing content is expected.
Content model:
If there is no src attribute, depends on the value of the type attribute, but must match script content restrictions.
If there is a src attribute, the element must be either empty or contain only script documentation that also matches script content restrictions.
Content attributes:
Global attributes
src
async
defer
type
charset
DOM interface:
interface HTMLScriptElement : HTMLElement {
           attribute DOMString src;
           attribute boolean async;
           attribute boolean defer;
           attribute DOMString type;
           attribute DOMString charset;
           attribute DOMString text;
};

The script element allows authors to include dynamic script and data blocks in their documents. The element does not represent content for the user.

When used to include dynamic scripts, the scripts may either be embedded inline or may be imported from an external file using the src attribute. If the language is not that described by "text/javascript", then the type attribute must be present, as described below.

When used to include data blocks (as opposed to scripts), the data must be embedded inline, the format of the data must be given using the type attribute, and the src attribute must not be specified.

The type attribute gives the language of the script or format of the data. If the attribute is present, its value must be a valid MIME type. The charset parameter must not be specified. The default, which is used if the attribute is absent, is "text/javascript".

The src attribute, if specified, gives the address of the external script resource to use. The value of the attribute must be a valid non-empty URL potentially surrounded by spaces identifying a script resource of the type given by the type attribute, if the attribute is present, or of the type "text/javascript", if the attribute is absent. A resource is a script resource of a given type if that type identifies a scripting language and the resource conforms with the requirements of that language's specification.

The charset attribute gives the character encoding of the external script resource. The attribute must not be specified if the src attribute is not present. If the attribute is set, its value must be a valid character encoding name, must be an ASCII case-insensitive match for the preferred MIME name for that encoding, and must match the encoding given in the charset parameter of the Content-Type metadata of the external file, if any. [IANACHARSET]

The async and defer attributes are boolean attributes that indicate how the script should be executed. The defer and async attributes must not be specified if the src attribute is not present.

There are three possible modes that can be selected using these attributes. If the async attribute is present, then the script will be executed asynchronously, as soon as it is available. If the async attribute is not present but the defer attribute is present, then the script is executed when the page has finished parsing. If neither attribute is present, then the script is fetched and executed immediately, before the user agent continues parsing the page.

The exact processing details for these attributes are, for mostly historical reasons, somewhat non-trivial, involving a number of aspects of HTML. The implementation requirements are therefore by necessity scattered throughout the specification. The algorithms below (in this section) describe the core of this processing, but these algorithms reference and are referenced by the parsing rules for script start and end tags in HTML, in foreign content, and in XML, the rules for the document.write() method, the handling of scripting, etc.

The defer attribute may be specified even if the async attribute is specified, to cause legacy Web browsers that only support defer (and not async) to fall back to the defer behavior instead of the synchronous blocking behavior that is the default.

Changing the src, type, charset, async, and defer attributes dynamically has no direct effect; these attribute are only used at specific times described below.

A script element has several associated pieces of state.

The first is a flag indicating whether or not the script block has been "already started". Initially, script elements must have this flag unset (script blocks, when created, are not "already started"). When a script element is cloned, the "already started" flag, if set, must be propagated to the clone when it is created.

The second is a flag indicating whether the element was "parser-inserted". Initially, script elements must have this flag unset. It is set by the HTML parser and the XML parser on script elements they insert and affects the processing of those elements.

The third is a flag indicating whether or not the script block is "ready to be parser-executed". Initially, script elements must have this flag unset (script blocks, when created, are not "ready to be parser-executed"). This flag is used only for elements that are also "parser-inserted", to let the parser know when to execute the script.

The fourth and fifth pieces of state are the script block's type and the script block's character encoding. They are determined when the script is run, based on the attributes on the element at that time.

When a script element that is neither marked as having "already started" nor marked as being "parser-inserted" experiences one of the events listed in the following list, the user agent must synchronously run the script element:

Running a script: When a script element is to be run, the user agent must act as follows:

  1. If either:

    • the script element has a type attribute and its value is the empty string, or
    • the script element has no type attribute but it has a language attribute and that attribute's value is the empty string, or
    • the script element has neither a type attribute nor a language attribute, then

    ...let the script block's type for this script element be "text/javascript".

    Otherwise, if the script element has a type attribute, let the script block's type for this script element be the value of that attribute with any leading or trailing sequences of space characters removed.

    Otherwise, the element has a non-empty language attribute; let the script block's type for this script element be the concatenation of the string "text/" followed by the value of the language attribute.

    The language attribute is never conforming, and is always ignored if there is a type attribute present.

  2. If the script element has a charset attribute, then let the script block's character encoding for this script element be the encoding given by the charset attribute.

    Otherwise, let the script block's character encoding for this script element be the same as the encoding of the document itself.

  3. If the script element has an event attribute and a for attribute, then run these substeps:

    1. Let for be the value of the for attribute.

    2. Let event be the value of the event attribute.

    3. Strip leading and trailing whitespace from event and for.

    4. If for is not an ASCII case-insensitive match for the string "window", then the user agent must abort these steps at this point. The script is not executed.

    5. If event is not an ASCII case-insensitive match for either the string "onload" or the string "onload()", then the user agent must abort these steps at this point. The script is not executed.

  4. If scripting is disabled for the script element, or if the user agent does not support the scripting language given by the script block's type for this script element, then the user agent must abort these steps at this point. The script is not executed.

  5. If the element has no src attribute, and its child nodes consist only of comment nodes and empty text nodes, then the user agent must abort these steps at this point. The script is not executed.

  6. The user agent must set the element's "already started" flag.

  7. If the element has a src attribute whose value is not the empty string, then the value of that attribute must be resolved relative to the element, and if that is successful, the specified resource must then be fetched, from the origin of the element's Document.

    If the src attribute's value is the empty string or if it could not be resolved, then the user agent must queue a task to fire a simple event named error at the element, and abort these steps.

    For historical reasons, if the URL is a javascript: URL, then the user agent must not, despite the requirements in the definition of the fetching algorithm, actually execute the script in the URL; instead the user agent must act as if it had received an empty HTTP 400 response.

    Once the resource's Content Type metadata is available, if it ever is, apply the algorithm for extracting an encoding from a Content-Type to it. If this returns an encoding, and the user agent supports that encoding, then let the script block's character encoding be that encoding.

    For performance reasons, user agents may start fetching the script as soon as the attribute is set, instead, in the hope that the element will be inserted into the document. Either way, once the element is inserted into the document, the load must have started. If the UA performs such prefetching, but the element is never inserted in the document, or the src attribute is dynamically changed, then the user agent will not execute the script, and the fetching process will have been effectively wasted.

  8. Then, the first of the following options that describes the situation must be followed:

    If the element has a src attribute, and the element has a defer attribute, and the element has been flagged as "parser-inserted", and the element does not have an async attribute

    The element must be added to the end of the list of scripts that will execute when the document has finished parsing.

    The task that the networking task source places on the task queue once the fetching algorithm has completed must set the element's "ready to be parser-executed" flag. The parser will handle executing the script.

    If the element has a src attribute, and the element has been flagged as "parser-inserted", and the element does not have an async attribute

    The element is the pending parsing-blocking script. (There can only be one such script at a time.)

    The task that the networking task source places on the task queue once the fetching algorithm has completed must set the element's "ready to be parser-executed" flag. The parser will handle executing the script.

    If the element does not have a src attribute, but there is a style sheet blocking scripts, and the element has been flagged as "parser-inserted"

    The element is the pending parsing-blocking script. (There can only be one such script at a time.)

    Set the element's "ready to be parser-executed" flag. The parser will handle executing the script.

    If the element has a src attribute

    The element must be added to the set of scripts that will execute as soon as possible.

    The task that the networking task source places on the task queue once the fetching algorithm has completed must execute the script block and then remove the element from the set of scripts that will execute as soon as possible.

    Otherwise
    The user agent must immediately execute the script block, even if other scripts are already executing.

Fetching an external script must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined above) has been run.

The pending parsing-blocking script is used by the parser.

Executing a script block: When the steps above require that the script block be executed, the user agent must act as follows:

If the load resulted in an error (for example a DNS error, or an HTTP 404 error)

Executing the script block must just consist of firing a simple event named error at the element.

If the load was successful
  1. Initialize the script block's source as follows:

    If the script is from an external file and the script block's type is a text-based language

    The contents of that file, interpreted as string of Unicode characters, are the script source.

    For each of the rows in the following table, starting with the first one and going down, if the file has as many or more bytes available than the number of bytes in the first column, and the first bytes of the file match the bytes given in the first column, then set the script block's character encoding to the encoding given in the cell in the second column of that row, irrespective of any previous value:

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

    This step looks for Unicode Byte Order Marks (BOMs).

    The file must then be converted to Unicode using the character encoding given by the script block's character encoding.

    If the script is from an external file and the script block's type is an XML-based language

    The external file is the script source. When it is later executed, it must be interpreted in a manner consistent with the specification defining the language given by the script block's type.

    If the script is inline and the script block's type is a text-based language

    The value of the text IDL attribute at the time the element's "already started" flag was set is the script source.

    If the script is inline and the script block's type is an XML-based language

    The child nodes of the script element at the time the element's "already started" flag was set are the script source.

  2. Create a script from the script element node, using the script block's source and the script block's type.

    This is where the script is compiled and actually executed.

  3. If the script is from an external file, fire a simple event named load at the script element.

    Otherwise, the script is internal; queue a task to fire a simple event named load at the script element.

The IDL attributes src, type, charset, async, and defer, each must reflect the respective content attributes of the same name.

script . text [ = value ]

Returns the contents of the element, ignoring child nodes that aren't text nodes.

Can be set, to replace the element's children with the given value.

The IDL attribute text must return a concatenation of the contents of all the text nodes that are direct children of the script element (ignoring any other nodes such as comments or elements), in tree order. On setting, it must act the same way as the textContent IDL attribute.

When inserted using the document.write() method, script elements execute (typically synchronously), but when inserted using innerHTML and outerHTML attributes, they do not execute at all.

In this example, two script elements are used. One embeds an external script, and the other includes some data.

<script src="game-engine.js"></script>
<script type="text/x-game-map">
........U.........e
o............A....e
.....A.....AAA....e
.A..AAA...AAAAA...e
</script>

The data in this case might be used by the script to generate the map of a video game. The data doesn't have to be used that way, though; maybe the map data is actually embedded in other parts of the page's markup, and the data block here is just used by the site's search engine to help users who are looking for particular features in their game maps.

The following sample shows how a script element can be used to define a function that is then used by other parts of the document. It also shows how a script element can be used to invoke script while the document is being parsed, in this case to initialize the form's output.

<script>
 function calculate(form) {
   var price = 52000;
   if (form.elements.brakes.checked)
     price += 1000;
   if (form.elements.radio.checked)
     price += 2500;
   if (form.elements.turbo.checked)
     price += 5000;
   if (form.elements.sticker.checked)
     price += 250;
   form.elements.result.value = price;
 }
</script>
<form name="pricecalc" onsubmit="return false">
 <fieldset>
  <legend>Work out the price of your car</legend>
  <p>Base cost: £52000.</p>
  <p>Select additional options:</p>
  <ul>
   <li><label><input type=checkbox name=brakes> Ceramic brakes (£1000)</label></li>
   <li><label><input type=checkbox name=radio> Satellite radio (£2500)</label></li>
   <li><label><input type=checkbox name=turbo> Turbo charger (£5000)</label></li>
   <li><label><input type=checkbox name=sticker> "XZ" sticker (£250)</label></li>
  </ul>
  <p>Total: £<output name=result onformchange="calculate(form)"></output></p>
 </fieldset>
 <script>
  document.forms.pricecalc.dispatchFormChange();
 </script>
</form>
4.3.1.1 Scripting languages

Status: Last call for comments

A user agent is said to support the scripting language if the script block's type is an ASCII case-insensitive match for the MIME type string of a scripting language that the user agent implements.

The following lists some MIME type strings and the languages to which they refer:

"application/ecmascript"
"application/javascript"
"application/x-ecmascript"
"application/x-javascript"
"text/ecmascript"
"text/javascript"
"text/javascript1.0"
"text/javascript1.1"
"text/javascript1.2"
"text/javascript1.3"
"text/javascript1.4"
"text/javascript1.5"
"text/jscript"
"text/livescript"
"text/x-ecmascript"
"text/x-javascript"
JavaScript. [ECMA262]
"text/javascript;e4x=1"
JavaScript with ECMAScript for XML. [ECMA357]

User agents may support other MIME types and other languages.

When examining types to determine if they support the language, user agents must not ignore unknown MIME parameters — types with unknown parameters must be assumed to be unsupported. The charset parameter must be treated as an unknown parameter for the purpose of comparing MIME types here.

4.3.1.2 Restrictions for contents of script elements

Status: Last call for comments

The textContent of a script element must match the script production in the following ABNF, the character set for which is Unicode. [ABNF]

script        = data1 *( escape [ script-start data3 ] "-->" data1 ) [ escape ]
escape        = "<!--" data2 *( script-start data3 script-end data2 )

data1         = <any string that doesn't contain a substring that matches not-data1>
not-data1     = "<!--"             

data2         = <any string that doesn't contain a substring that matches not-data2>
not-data2     = script-start / "-->"  

data3         = <any string that doesn't contain a substring that matches not-data3>
not-data3     = script-end / "-->"

script-start  = lt       s c r i p t tag-end
script-end    = lt slash s c r i p t tag-end

lt            =  %x003C ; U+003C LESS-THAN SIGN character (<)
slash         =  %x002F ; U+002F SOLIDUS character (/)

s             =  %x0053 ; U+0053 LATIN CAPITAL LETTER S
s             =/ %x0073 ; U+0073 LATIN SMALL LETTER S
c             =  %x0043 ; U+0043 LATIN CAPITAL LETTER C
c             =/ %x0063 ; U+0063 LATIN SMALL LETTER C
r             =  %x0052 ; U+0052 LATIN CAPITAL LETTER R
r             =/ %x0072 ; U+0072 LATIN SMALL LETTER R
i             =  %x0049 ; U+0049 LATIN CAPITAL LETTER I
i             =/ %x0069 ; U+0069 LATIN SMALL LETTER I
p             =  %x0050 ; U+0050 LATIN CAPITAL LETTER P
p             =/ %x0070 ; U+0070 LATIN SMALL LETTER P
t             =  %x0054 ; U+0054 LATIN CAPITAL LETTER T
t             =/ %x0074 ; U+0074 LATIN SMALL LETTER T

tag-end       =  %x0009 ; U+0009 CHARACTER TABULATION
tag-end       =/ %x000A ; U+000A LINE FEED (LF)
tag-end       =/ %x000C ; U+000C FORM FEED (FF)
tag-end       =/ %x0020 ; U+0020 SPACE
tag-end       =/ %x002F ; U+002F SOLIDUS (/)
tag-end       =/ %x003E ; U+003E GREATER-THAN SIGN (>)

When a script element contains script documentation, there are further restrictions on the contents of the element, as described in the section below.

4.3.1.3 Inline documentation for external scripts

Status: Last call for comments

If a script element's src attribute is specified, then the contents of the script element, if any, must be such that the value of the text IDL attribute, which is derived from the element's contents, matches the documentation production in the following ABNF, the character set for which is Unicode. [ABNF]

documentation = *( *( space / tab / comment ) [ line-comment ] newline )
comment       = slash star *( not-star / star not-slash ) 1*star slash
line-comment  = slash slash *not-newline

; characters
tab           = %x0009 ; U+0009 TAB
newline       = %x000A ; U+000A LINE FEED (LF)
space         = %x0020 ; U+0020 SPACE
star          = %x002A ; U+002A ASTERISK (*)
slash         = %x002F ; U+002F SOLIDUS (/)
not-newline   = %x0000-0009 / %x000B-10FFFF
                ; a Unicode character other than U+000A LINE FEED (LF)
not-star      = %x0000-0029 / %x002B-10FFFF
                ; a Unicode character other than U+002A ASTERISK (*)
not-slash     = %x0000-002E / %x0030-10FFFF
                ; a Unicode character other than U+002F SOLIDUS (/)

This corresponds to putting the contents of the element in JavaScript comments.

This requirement is in addition to the earlier restrictions on the syntax of contents of script elements.

This allows authors to include documentation, such as license information or API information, inside their documents while still referring to external script files. The syntax is constrained so that authors don't accidentally include what looks like valid script while also providing a src attribute.

<script src="cool-effects.js">
 // create new instances using:
 //    var e = new Effect();
 // start the effect using .play, stop using .stop:
 //    e.play();
 //    e.stop();
</script>

4.3.2 The noscript element

Status: Last call for comments

Categories
Metadata content.
Flow content.
Phrasing content.
Contexts in which this element may be used:
In a head element of an HTML document, if there are no ancestor noscript elements.
Where phrasing content is expected in HTML documents, if there are no ancestor noscript elements.
Content model:
When scripting is disabled, in a head element: in any order, zero or more link elements, zero or more style elements, and zero or more meta elements.
When scripting is disabled, not in a head element: transparent, but there must be no noscript element descendants.
Otherwise: text that conforms to the requirements given in the prose.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The noscript element represents nothing if scripting is enabled, and represents its children if scripting is disabled. It is used to present different markup to user agents that support scripting and those that don't support scripting, by affecting how the document is parsed.

When used in HTML documents, the allowed content model is as follows:

In a head element, if scripting is disabled for the noscript element

The noscript element must contain only link, style, and meta elements.

In a head element, if scripting is enabled for the noscript element

The noscript element must contain only text, except that invoking the HTML fragment parsing algorithm with the noscript element as the context element and the text contents as the input must result in a list of nodes that consists only of link, style, and meta elements that would be conforming if they were children of the noscript element, and no parse errors.

Outside of head elements, if scripting is disabled for the noscript element

The noscript element's content model is transparent, with the additional restriction that a noscript element must not have a noscript element as an ancestor (that is, noscript can't be nested).

Outside of head elements, if scripting is enabled for the noscript element

The noscript element must contain only text, except that the text must be such that running the following algorithm results in a conforming document with no noscript elements and no script elements, and such that no step in the algorithm causes an HTML parser to flag a parse error:

  1. Remove every script element from the document.
  2. Make a list of every noscript element in the document. For every noscript element in that list, perform the following steps:
    1. Let the parent element be the parent element of the noscript element.
    2. Take all the children of the parent element that come before the noscript element, and call these elements the before children.
    3. Take all the children of the parent element that come after the noscript element, and call these elements the after children.
    4. Let s be the concatenation of all the text node children of the noscript element.
    5. Set the innerHTML attribute of the parent element to the value of s. (This, as a side-effect, causes the noscript element to be removed from the document.)
    6. Insert the before children at the start of the parent element, preserving their original relative order.
    7. Insert the after children at the end of the parent element, preserving their original relative order.

All these contortions are required because, for historical reasons, the noscript element is handled differently by the HTML parser based on whether scripting was enabled or not when the parser was invoked.

The noscript element must not be used in XML documents.

The noscript element is only effective in the HTML syntax, it has no effect in the XHTML syntax.

The noscript element has no other requirements. In particular, children of the noscript element are not exempt from form submission, scripting, and so forth, even when scripting is enabled for the element.

In the following example, a noscript element is used to provide fallback for a script.

<form action="calcSquare.php">
 <p>
  <label for=x>Number</label>:
  <input id="x" name="x" type="number">
 </p>
 <script>
  var x = document.getElementById('x');
  var output = document.createElement('p');
  output.textContent = 'Type a number; it will be squared right then!';
  x.form.appendChild(output);
  x.form.onsubmit = function () { return false; }
  x.oninput = function () {
    var v = x.valueAsNumber;
    output.textContent = v + ' squared is ' + v * v;
  };
 </script>
 <noscript>
  <input type=submit value="Calculate Square">
 </noscript>
</form>

When script is disabled, a button appears to do the calculation on the server side. When script is enabled, the value is computed on-the-fly instead.

The noscript element is a blunt instrument. Sometimes, scripts might be enabled, but for some reason the page's script might fail. For this reason, it's generally better to avoid using noscript, and to instead design the script to change the page from being a scriptless page to a scripted page on the fly, as in the next example:

<form action="calcSquare.php">
 <p>
  <label for=x>Number</label>:
  <input id="x" name="x" type="number">
 </p>
 <input id="submit" type=submit value="Calculate Square">
 <script>
  var x = document.getElementById('x');
  var output = document.createElement('p');
  output.textContent = 'Type a number; it will be squared right then!';
  x.form.appendChild(output);
  x.form.onsubmit = function () { return false; }
  x.oninput = function () {
    var v = x.valueAsNumber;
    output.textContent = v + ' squared is ' + v * v;
  };
  var submit = document.getElementById('submit');
  submit.parentNode.removeChild(submit);
 </script>
</form>

The above technique is also useful in XHTML, since noscript is not supported in the XHTML syntax.

4.4 Sections

Status: Last call for comments

4.4.1 The body element

Status: Last call for comments

Categories
Sectioning root.
Contexts in which this element may be used:
As the second element in an html element.
Content model:
Flow content.
Content attributes:
Global attributes
onafterprint
onbeforeprint
onbeforeunload
onblur
onerror
onfocus
onhashchange
onload
onmessage
onoffline
ononline
onpagehide
onpageshow
onpopstate
onredo
onresize
onstorage
onundo
onunload
DOM interface:
interface HTMLBodyElement : HTMLElement {
           attribute Function onafterprint;
           attribute Function onbeforeprint;
           attribute Function onbeforeunload;
           attribute Function onblur;
           attribute Function onerror;
           attribute Function onfocus;
           attribute Function onhashchange;
           attribute Function onload;
           attribute Function onmessage;
           attribute Function onoffline;
           attribute Function ononline;
           attribute Function onpopstate;
           attribute Function onpagehide;
           attribute Function onpageshow;
           attribute Function onredo;
           attribute Function onresize;
           attribute Function onstorage;
           attribute Function onundo;
           attribute Function onunload;
};

The body element represents the main content of the document.

In conforming documents, there is only one body element. The document.body IDL attribute provides scripts with easy access to a document's body element.

Some DOM operations (for example, parts of the drag and drop model) are defined in terms of "the body element". This refers to a particular element in the DOM, as per the definition of the term, and not any arbitrary body element.

The body element exposes as event handler content attributes a number of the event handlers of the Window object. It also mirrors their event handler IDL attributes.

The onblur, onerror, onfocus, and onload event handlers of the Window object, exposed on the body element, shadow the generic event handlers with the same names normally supported by HTML elements.

Thus, for example, a bubbling error event fired on a child of the body element of a Document would first trigger the onerror event handler content attributes of that element, then that of the root html element, and only then would it trigger the onerror event handler content attribute on the body element. This is because the event would bubble from the target, to the body, to the html, to the Document, to the Window, and the event handler on the body is watching the Window not the body. A regular event listener attached to the body using addEventListener(), however, would fire when the event bubbled through the body and not when it reaches the Window object.

This page updates an indicator to show whether or not the user is online:

<!DOCTYPE HTML>
<html>
 <head>
  <title>Online or offline?</title>
  <script>
   function update(online) {
     document.getElementById('status').textContent =
       online ? 'Online' : 'Offline';
   }
  </script>
 </head>
 <body ononline="update(true)"
       onoffline="update(false)"
       onload="update(navigator.onLine)">
  <p>You are: <span id="status">(Unknown)</span></p>
 </body>
</html>

4.4.2 The section element

Status: Last call for comments

Categories
Flow content.
Sectioning content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

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

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.

Authors are encouraged to use the article element instead of the section element when it would make sense to syndicate the contents of the element.

The section element is not a generic container element. When an element is needed for styling purposes or as a convenience for scripting, authors are encouraged to use the div element instead. A general rule is that the section element is appropriate only if the element's contents would be listed explicitly in the document's outline.

In the following example, we see an article (part of a larger Web page) about apples, containing two short sections.

<article>
 <hgroup>
  <h1>Apples</h1>
  <h2>Tasty, delicious fruit!</h2>
 </hgroup>
 <p>The apple is the pomaceous fruit of the apple tree.</p>
 <section>
  <h1>Red Delicious</h1>
  <p>These bright red apples are the most common found in many
  supermarkets.</p>
 </section>
 <section>
  <h1>Granny Smith</h1>
  <p>These juicy, green apples make a great filling for
  apple pies.</p>
 </section>
</article>

Notice how the use of section means that the author can use h1 elements throughout, without having to worry about whether a particular section is at the top level, the second level, the third level, and so on.

Here is a graduation programme with two sections, one for the list of people graduating, and one for the description of the ceremony.

<!DOCTYPE Html>
<Html
 ><Head
   ><Title
     >Graduation Ceremony Summer 2022</Title
   ></Head
 ><Body
   ><H1
     >Graduation</H1
   ><Section
     ><H1
       >Ceremony</H1
     ><P
       >Opening Procession</P
     ><P
       >Speech by Validactorian</P
     ><P
       >Speech by Class President</P
     ><P
       >Presentation of Diplomas</P
     ><P
       >Closing Speech by Headmaster</P
   ></Section
   ><Section
     ><H1
       >Graduates</H1
     ><Ul
       ><Li
         >Molly Carpenter</Li
       ><Li
         >Anastasia Luccio</Li
       ><Li
         >Ebenezar McCoy</Li
       ><Li
         >Karrin Murphy</Li
       ><Li
         >Thomas Raith</Li
       ><Li
         >Susan Rodriguez</Li
     ></Ul
   ></Section
 ></Body
></Html>

4.4.3 The nav element

Status: Last call for comments

Categories
Flow content.
Sectioning content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links.

Not all groups of links on a page need to be in a nav element — only sections that consist of major navigation blocks are appropriate for the nav element. In particular, it is common for footers to have a short list of links to various pages of a site, such as the terms of service, the home page, and a copyright page. The footer element alone is sufficient for such cases, without a nav element.

User agents (such as screen readers) that are targeted at users who can benefit from navigation information being omitted in the initial rendering, or who can benefit from navigation information being immediately available, can use this element as a way to determine what content on the page to initially skip and/or provide on request.

In the following example, the page has several places where links are present, but only one of those places is considered a navigation section.

<body>
 <header>
  <h1>Wake up sheeple!</h1>
  <p><a href="news.html">News</a> -
     <a href="blog.html">Blog</a> -
     <a href="forums.html">Forums</a></p>
  <p>Last Modified: <time>2009-04-01</time></p>
  <nav>
   <h1>Navigation</h1>
   <ul>
    <li><a href="articles.html">Index of all articles</a></li>
    <li><a href="today.html">Things sheeple need to wake up for today</a></li>
    <li><a href="successes.html">Sheeple we have managed to wake</a></li>
   </ul>
  </nav>
 </header>
 <div>
  <article>
   <header>
    <h1>My Day at the Beach</h1>
   </header>
   <div>
    <p>Today I went to the beach and had a lot of fun.</p>
    ...more content...
   </div>
   <footer>
    <p>Posted <time pubdate datetime="2009-10-10T14:36-08:00">Thursday</time>.</p>
   </footer>
  </article>
  ...more blog posts...
 </div>
 <footer>
  <p>Copyright © 2006 The Example Company</p>
  <p><a href="about.html">About</a> -
     <a href="policy.html">Privacy Policy</a> -
     <a href="contact.html">Contact Us</a></p>
 </footer>
</body>

Notice the div elements being used to wrap all the contents of the page other than the header and footer, and all the contents of the blog entry other than its header and footer.

In the following example, there are two nav elements, one for primary navigation around the site, and one for secondary navigation around the page itself.

<body>
 <h1>The Wiki Center Of Exampland</h1>
 <nav>
  <ul>
   <li><a href="/">Home</a></li>
   <li><a href="/events">Current Events</a></li>
   ...more...
  </ul>
 </nav>
 <article>
  <header>
   <h1>Demos in Exampland</h1>
   <p>Written by A. N. Other.</p>
  </header>
  <nav>
   <ul>
    <li><a href="#public">Public demonstrations</a></li>
    <li><a href="#destroy">Demolitions</a></li>
    ...more...
   </ul>
  </nav>
  <div>
   <section id="public">
    <h1>Public demonstrations</h1>
    <p>...more...</p>
   </section>
   <section id="destroy">
    <h1>Demolitions</h1>
    <p>...more...</p>
   </section>
   ...more...
  </div>
  <footer>
   <p><a href="?edit">Edit</a> | <a href="?delete">Delete</a> | <a href="?Rename">Rename</a></p>
  </footer>
 </article>
 <footer>
  <p><small>© copyright 1998 Exampland Emperor</small></p>
 </footer>
</body>

4.4.4 The article element

Status: Last call for comments

Categories
Flow content.
Sectioning content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The article element represents a self-contained composition in a document, page, application, or site and that is intended to be independently distributable or reusable, e.g. in syndication. This could be a forum post, a magazine or newspaper article, a blog entry, a user-submitted comment, an interactive widget or gadget, or any other independent item of content.

When article elements are nested, the inner article elements represent articles that are in principle related to the contents of the outer article. For instance, a blog entry on a site that accepts user-submitted comments could represent the comments as article elements nested within the article element for the blog entry.

Author information associated with an article element (q.v. the address element) does not apply to nested article elements.

When used specifically with content to be redistributed in syndication, the article element is similar in purpose to the entry element in Atom. [ATOM]

The time element's pubdate attribute can be used to provide the publication date for an article element.

This example shows a blog post using the article element:

<article>
 <header>
  <h1>The Very First Rule of Life</h1>
  <p><time pubdate datetime="2009-10-09T14:28-08:00"></time></p>
 </header>
 <p>If there's a microphone anywhere near you, assume it's hot and
 sending whatever you're saying to the world. Seriously.</p>
 <p>...</p>
 <footer>
  <a href="?comments=1">Show comments...</a>
 </footer>
</article>

Here is that same blog post, but showing some of the comments:

<article>
 <header>
  <h1>The Very First Rule of Life</h1>
  <p><time pubdate datetime="2009-10-09T14:28-08:00"></time></p>
 </header>
 <p>If there's a microphone anywhere near you, assume it's hot and
 sending whatever you're saying to the world. Seriously.</p>
 <p>...</p>
 <section>
  <h1>Comments</h1>
  <article>
   <footer>
    <p>Posted by: George Washington</p>
    <p><time pubdate datetime="2009-10-10T19:10-08:00"></time></p>
   </footer>
   <p>Yeah! Especially when talking about your lobbyist friends!</p>
  </article>
  <article>
   <footer>
    <p>Posted by: George Hammond</p>
    <p><time pubdate datetime="2009-10-10T19:15-08:00"></time></p>
   </footer>
   <p>Hey, you have the same first name as me.</p>
  </article>
 </section>
</article>

Notice the use of footer to give the information each comment (such as who wrote it and when): the footer element can appear at the start of its section when appropriate, such as in this case. (Using header in this case wouldn't be wrong either; it's mostly a matter of authoring preference.)

4.4.5 The aside element

Status: Last call for comments

Categories
Flow content.
Sectioning content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography.

The element can be used for typographical effects like pull quotes or sidebars, for advertising, for groups of nav elements, and for other content that is considered separate from the main content of the page.

It's not appropriate to use the aside element just for parentheticals, since those are part of the main flow of the document.

The following example shows how an aside is used to mark up background material on Switzerland in a much longer news story on Europe.

<aside>
 <h1>Switzerland</h1>
 <p>Switzerland, a land-locked country in the middle of geographic
 Europe, has not joined the geopolitical European Union, though it is
 a signatory to a number of European treaties.</p>
</aside>

The following example shows how an aside is used to mark up a pull quote in a longer article.

...

<p>He later joined a large company, continuing on the same work.
<q>I love my job. People ask me what I do for fun when I'm not at
work. But I'm paid to do my hobby, so I never know what to
answer. Some people wonder what they would do if they didn't have to
work... but I know what I would do, because I was unemployed for a
year, and I filled that time doing exactly what I do now.</q></p>

<aside>
 <q> People ask me what I do for fun when I'm not at work. But I'm
 paid to do my hobby, so I never know what to answer. </q>
</aside>

<p>Of course his work — or should that be hobby? —
isn't his only passion. He also enjoys other pleasures.</p>

...

The following extract shows how aside can be used for blogrolls and other side content on a blog:

<body>
 <header>
  <h1>My wonderful blog</h1>
  <p>My tagline</p>
 </header>
 <aside>
  <!-- this aside contains two sections that are tangentially related
  to the page, namely, links to other blogs, and links to blog posts
  from this blog -->
  <nav>
   <h1>My blogroll</h1>
   <ul>
    <li><a href="http://blog.example.com/">Example Blog</a>
   </ul>
  </nav>
  <nav>
   <h1>Archives</h1>
   <ol reversed>
    <li><a href="/last-post">My last post</a>
    <li><a href="/first-post">My first post</a>
   </ol>
  </nav>
 </aside>
 <aside>
  <!-- this aside is tangentially related to the page also, it
  contains twitter messages from the blog author -->
  <h1>Twitter Feed</h1>
  <blockquote cite="http://twitter.example.net/t31351234">
   I'm on vacation, writing my blog.
  </blockquote>
  <blockquote cite="http://twitter.example.net/t31219752">
   I'm going to go on vacation soon.
  </blockquote>
 </aside>
 <article>
  <!-- this is a blog post -->
  <h1>My last post</h1>
  <p>This is my last post.</p>
  <footer>
   <p><a href="/last-post" rel=bookmark>Permalink</a>
  </footer>
 </article>
 <article>
  <!-- this is also a blog post -->
  <h1>My first post</h1>
  <p>This is my first post.</p>
  <aside>
   <!-- this aside is about the blog post, since it's inside the
   <article> element; it would be wrong, for instance, to put the
   blogroll here, since the blogroll isn't really related to this post
   specifically, only to the page as a whole -->
   <h1>Posting</h1>
   <p>While I'm thinking about it, I wanted to say something about
   posting. Posting is fun!</p>
  </aside>
  <footer>
   <p><a href="/first-post" rel=bookmark>Permalink</a>
  </footer>
 </article>
 <footer>
  <nav>
   <a href="/archives">Archives</a> —
   <a href="/about">About me</a> —
   <a href="/copyright">Copyright</a>
  </nav>
 </footer>
</body>

4.4.6 The h1, h2, h3, h4, h5, and h6 elements

Categories
Flow content.
Heading content.
formatBlock candidate.
Contexts in which this element may be used:
As a child of an hgroup element.
Where flow content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
interface HTMLHeadingElement : HTMLElement {};

These elements represent headings for their sections.

The semantics and meaning of these elements are defined in the section on headings and sections.

These elements have a rank given by the number in their name. The h1 element is said to have the highest rank, the h6 element has the lowest rank, and two elements with the same name have equal rank.

These two snippets are equivalent:

<body>
<h1>Let's call it a draw(ing surface)</h1>
<h2>Diving in</h2>
<h2>Simple shapes</h2>
<h2>Canvas coordinates</h2>
<h3>Canvas coordinates diagram</h3>
<h2>Paths</h2>
</body>
<body>
 <h1>Let's call it a draw(ing surface)</h1>
 <section>
  <h1>Diving in</h1>
 </section>
 <section>
  <h1>Simple shapes</h1>
 </section>
 <section>
  <h1>Canvas coordinates</h1>
  <section>
   <h1>Canvas coordinates diagram</h1>
  </section>
 </section>
 <section>
  <h1>Paths</h1>
 </section>
</body>

4.4.7 The hgroup element

Status: Last call for comments

Categories
Flow content.
Heading content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
One or more h1, h2, h3, h4, h5, and/or h6 elements.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The hgroup element represents the heading of a section. The element is used to group a set of h1h6 elements when the heading has multiple levels, such as subheadings, alternative titles, or taglines.

For the purposes of document summaries, outlines, and the like, the text of hgroup elements is defined to be the text of the highest ranked h1h6 element descendant of the hgroup element, if there are any such elements, and the first such element if there are multiple elements with that rank. If there are no such elements, then the text of the hgroup element is the empty string.

Other elements of heading content in the hgroup element indicate subheadings or subtitles.

The rank of an hgroup element is the rank of the highest-ranked h1h6 element descendant of the hgroup element, if there are any such elements, or otherwise the same as for an h1 element (the highest rank).

The section on headings and sections defines how hgroup elements are assigned to individual sections.

Here are some examples of valid headings. In each case, the emphasized text represents the text that would be used as the heading in an application extracting heading data and ignoring subheadings.

<hgroup>
 <h1>The reality dysfunction</h1>
 <h2>Space is not the only void</h2>
</hgroup>
<hgroup>
 <h1>Dr. Strangelove</h1>
 <h2>Or: How I Learned to Stop Worrying and Love the Bomb</h2>
</hgroup>

The point of using hgroup in these examples is to mask the h2 element (which acts as a secondary title) from the outline algorithm.

4.4.8 The header element

Status: Last call for comments

Categories
Flow content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no header or footer element descendants.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The header element represents a group of introductory or navigational aids.

A header element is intended to usually contain the section's heading (an h1h6 element or an hgroup element), but this is not required. The header element can also be used to wrap a section's table of contents, a search form, or any relevant logos.

Here are some sample headers. This first one is for a game:

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

The following snippet shows how the element can be used to mark up a specification's header:

<header>
 <hgroup>
  <h1>Scalable Vector Graphics (SVG) 1.2</h1>
  <h2>W3C Working Draft 27 October 2004</h2>
 </hgroup>
 <dl>
  <dt>This version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20041027/">http://www.w3.org/TR/2004/WD-SVG12-20041027/</a></dd>
  <dt>Previous version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20040510/">http://www.w3.org/TR/2004/WD-SVG12-20040510/</a></dd>
  <dt>Latest version of SVG 1.2:</dt>
  <dd><a href="http://www.w3.org/TR/SVG12/">http://www.w3.org/TR/SVG12/</a></dd>
  <dt>Latest SVG Recommendation:</dt>
  <dd><a href="http://www.w3.org/TR/SVG/">http://www.w3.org/TR/SVG/</a></dd>
  <dt>Editor:</dt>
  <dd>Dean Jackson, W3C, <a href="mailto:dean@w3.org">dean@w3.org</a></dd>
  <dt>Authors:</dt>
  <dd>See <a href="#authors">Author List</a></dd>
 </dl>
 <p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notic ...
</header>

The header element is not sectioning content; it doesn't introduce a new section.

In this example, the page has a page heading given by the h1 element, and two subsections whose headings are given by h2 elements. The content after the header element is still part of the last subsection started in the header element, because the header element doesn't take part in the outline algorithm.

<body>
 <header>
  <h1>Little Green Guys With Guns</h1>
  <nav>
   <ul>
    <li><a href="/games">Games</a>
    <li><a href="/forum">Forum</a>
    <li><a href="/download">Download</a>
   </ul>
  </nav>
  <h2>Important News</h2> <!-- this starts a second subsection -->
  <!-- this is part of the subsection entitled "Important News" -->
  <p>To play today's games you will need to update your client.</p>
  <h2>Games</h2> <!-- this starts a third subsection -->
 </header>
 <p>You have three active games:</p>
 <!-- this is still part of the subsection entitled "Games" -->
 ...

Status: Last call for comments

Categories
Flow content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no header or footer element descendants.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The footer element represents a footer for its nearest ancestor sectioning content or sectioning root element. A footer typically contains information about its section such as who wrote it, links to related documents, copyright data, and the like.

Contact information for the author or editor of a section belongs in an address element, possibly itself inside a footer.

Footers don't necessarily have to appear at the end of a section, though they usually do.

When the footer element contains entire sections, they represent appendices, indexes, long colophons, verbose license agreements, and other such content.

The footer element is not sectioning content; it doesn't introduce a new section.

When the nearest ancestor sectioning content or sectioning root element is the body element, then it applies to the whole page.

Here is a page with two footers, one at the top and one at the bottom, with the same content:

<body>
 <footer><a href="../">Back to index...</a></footer>
 <hgroup>
  <h1>Lorem ipsum</h1>
  <h2>The ipsum of all lorems</h2>
 </hgroup>
 <p>A dolor sit amet, consectetur adipisicing elit, sed do eiusmod
 tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
 veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
 ea commodo consequat. Duis aute irure dolor in reprehenderit in
 voluptate velit esse cillum dolore eu fugiat nulla
 pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
 culpa qui officia deserunt mollit anim id est laborum.</p>
 <footer><a href="../">Back to index...</a></footer>
</body>

Here is an example which shows the footer element being used both for a site-wide footer and for a section footer.

<!DOCTYPE HTML>
<HTML><HEAD>
<TITLE>The Ramblings of a Scientist</TITLE>
<BODY>
<H1>The Ramblings of a Scientist</H1>
<ARTICLE>
 <H1>Episode 15</H1>
 <VIDEO SRC="/fm/015.ogv" CONTROLS PRELOAD>
  <P><A HREF="/fm/015.ogv">Download video</A>.</P>
 </VIDEO>
 <FOOTER> <!-- footer for article -->
  <P>Published <TIME PUBDATE DATETIME="2009-10-21T18:26-07:00"></TIME></P>
 </FOOTER>
</ARTICLE>
<ARTICLE>
 <H1>My Favorite Trains</H1>
 <P>I love my trains. My favorite train of all time is a Köf.</P>
 <P>It is fun to see them pull some coal cars because they look so
 dwarfed in comparison.</P>
 <FOOTER> <!-- footer for article -->
  <P>Published <TIME PUBDATE DATETIME="2009-09-15T14:54-07:00"></TIME></P>
 </FOOTER>
</ARTICLE>
<FOOTER> <!-- site wide footer -->
 <NAV>
  <P><A HREF="/credits.html">Credits</A> —
     <A HREF="/tos.html">Terms of Service</A> —
     <A HREF="/index.html">Blog Index</A></P>
 </NAV>
 <P>Copyright © 2009 Gordon Freeman</P>
</FOOTER>
</BODY>
</HTML>

4.4.10 The address element

Status: Last call for comments

Categories
Flow content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no heading content descendants, no sectioning content descendants, and no header, footer, or address element descendants.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The address element represents the contact information for its nearest article or body element ancestor. If that is the body element, then the contact information applies to the document as a whole.

For example, a page at the W3C Web site related to HTML might include the following contact information:

<ADDRESS>
 <A href="../People/Raggett/">Dave Raggett</A>,
 <A href="../People/Arnaud/">Arnaud Le Hors</A>,
 contact persons for the <A href="Activity">W3C HTML Activity</A>
</ADDRESS>

The address element must not be used to represent arbitrary addresses (e.g. postal addresses), unless those addresses are in fact the relevant contact information. (The p element is the appropriate element for marking up postal addresses in general.)

The address element must not contain information other than contact information.

For example, the following is non-conforming use of the address element:

<ADDRESS>Last Modified: 1999/12/24 23:37:50</ADDRESS>

Typically, the address element would be included along with other information in a footer element.

The contact information for a node node is a collection of address elements defined by the first applicable entry from the following list:

If node is an article element
If node is a body element

The contact information consists of all the address elements that have node as an ancestor and do not have another body or article element ancestor that is a descendant of node.

If node has an ancestor element that is an article element
If node has an ancestor element that is a body element

The contact information of node is the same as the contact information of the nearest article or body element ancestor, whichever is nearest.

If node's Document has a body element

The contact information of node is the same as the contact information the body element of the Document.

Otherwise

There is no contact information for node.

User agents may expose the contact information of a node to the user, or use it for other purposes, such as indexing sections based on the sections' contact information.

4.4.11 Headings and sections

Status: Last call for comments

The h1h6 elements and the hgroup element are headings.

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

Certain elements are said to be sectioning roots, including blockquote and td elements. These elements can have their own outlines, but the sections and headings inside these elements do not contribute to the outlines of their ancestors.

Sectioning content elements are always considered subsections of their nearest ancestor sectioning root or their nearest ancestor element of sectioning content, whichever is nearest, regardless of what implied sections other headings may have created.

For the following fragment:

<body>
 <h1>Foo</h1>
 <h2>Bar</h2>
 <blockquote>
  <h3>Bla</h3>
 </blockquote>
 <p>Baz</p>
 <h2>Quux</h2>
 <section>
  <h3>Thud</h3>
 </section>
 <p>Grunt</p>
</body>

...the structure would be:

  1. Foo (heading of explicit body section, containing the "Grunt" paragraph)
    1. Bar (heading starting implied section, containing a block quote and the "Baz" paragraph)
    2. Quux (heading starting implied section with no content other than the heading itself)
    3. Thud (heading of explicit section section)

Notice how the section ends the earlier implicit section so that a later paragraph ("Grunt") is back at the top level.

Sections may contain headings of any rank, but authors are strongly encouraged to either use only h1 elements, or to use elements of the appropriate rank for the section's nesting level.

Authors are also encouraged to explicitly wrap sections in elements of sectioning content, instead of relying on the implicit sections generated by having multiple headings in one element of sectioning content.

For example, the following is correct:

<body>
 <h4>Apples</h4>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <h6>Sweet</h6>
  <p>Red apples are sweeter than green ones.</p>
  <h1>Color</h1>
  <p>Apples come in various colors.</p>
 </section>
</body>

However, the same document would be more clearly expressed as:

<body>
 <h1>Apples</h1>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <section>
   <h3>Sweet</h3>
   <p>Red apples are sweeter than green ones.</p>
  </section>
 </section>
 <section>
  <h2>Color</h2>
  <p>Apples come in various colors.</p>
 </section>
</body>

Both of the documents above are semantically identical and would produce the same outline in compliant user agents.

4.4.11.1 Creating an outline

Status: Last call for comments

This section defines an algorithm for creating an outline for a sectioning content element or a sectioning root element. It is defined in terms of a walk over the nodes of a DOM tree, in tree order, with each node being visited when it is entered and when it is exited during the walk.

The outline for a sectioning content element or a sectioning root element consists of a list of one or more potentially nested sections. A section is a container that corresponds to some nodes in the original DOM tree. Each section can have one heading associated with it, and can contain any number of further nested sections. The algorithm for the outline also associates each node in the DOM tree with a particular section and potentially a heading. (The sections in the outline aren't section elements, though some may correspond to such elements — they are merely conceptual sections.)

The following markup fragment:

<body>
 <h1>A</h1>
 <p>B</p>
 <h2>C</h2>
 <p>D</p>
 <h2>E</h2>
 <p>F</p>
</body>

...results in the following outline being created for the body node (and thus the entire document):

  1. Section created for body node.

    Associated with heading "A".

    Also associated with paragraph "B".

    Nested sections:

    1. Section implied for first h2 element.

      Associated with heading "C".

      Also associated with paragraph "D".

      No nested sections.

    2. Section implied for second h2 element.

      Associated with heading "E".

      Also associated with paragraph "F".

      No nested sections.

The algorithm that must be followed during a walk of a DOM subtree rooted at a sectioning content element or a sectioning root element to determine that element's outline is as follows:

  1. Let current outlinee be null. (It holds the element whose outline is being created.)

  2. Let current section be null. (It holds a pointer to a section, so that elements in the DOM can all be associated with a section.)

  3. Create a stack to hold elements, which is used to handle nesting. Initialize this stack to empty.

  4. As you walk over the DOM in tree order, trigger the first relevant step below for each element as you enter and exit it.

    If the top of the stack is an element, and you are exiting that element

    The element being exited is a heading content element.

    Pop that element from the stack.

    If the top of the stack is a heading content element

    Do nothing.

    When entering a sectioning content element or a sectioning root element

    If current outlinee is not null, and the current section has no heading, create an implied heading and let that be the heading for the current section.

    If current outlinee is not null, push current outlinee onto the stack.

    Let current outlinee be the element that is being entered.

    Let current section be a newly created section for the current outlinee element.

    Let there be a new outline for the new current outlinee, initialized with just the new current section as the only section in the outline.

    When exiting a sectioning content element, if the stack is not empty

    Pop the top element from the stack, and let the current outlinee be that element.

    Let current section be the last section in the outline of the current outlinee element.

    Append the outline of the sectioning content element being exited to the current section. (This does not change which section is the last section in the outline.)

    When exiting a sectioning root element, if the stack is not empty

    Run these steps:

    1. Pop the top element from the stack, and let the current outlinee be that element.

    2. Let current section be the last section in the outline of the current outlinee element.

    3. Finding the deepest child: If current section has no child sections, stop these steps.

    4. Let current section be the last child section of the current current section.

    5. Go back to the substep labeled finding the deepest child.

    When exiting a sectioning content element or a sectioning root element

    The current outlinee is the element being exited.

    Let current section be the first section in the outline of the current outlinee element.

    Skip to the next step in the overall set of steps. (The walk is over.)

    If the current outlinee is null

    Do nothing.

    When entering a heading content element

    If the current section has no heading, let the element being entered be the heading for the current section.

    Otherwise, if the element being entered has a rank equal to or greater than the heading of the last section of the outline of the current outlinee, then create a new section and append it to the outline of the current outlinee element, so that this new section is the new last section of that outline. Let current section be that new section. Let the element being entered be the new heading for the current section.

    Otherwise, run these substeps:

    1. Let candidate section be current section.

    2. If the element being entered has a rank lower than the rank of the heading of the candidate section, then create a new section, and append it to candidate section. (This does not change which section is the last section in the outline.) Let current section be this new section. Let the element being entered be the new heading for the current section. Abort these substeps.

    3. Let new candidate section be the section that contains candidate section in the outline of current outlinee.

    4. Let candidate section be new candidate section.

    5. Return to step 2.

    Push the element being entered onto the stack. (This causes the algorithm to skip any descendants of the element.)

    Recall that h1 has the highest rank, and h6 has the lowest rank.

    Otherwise

    Do nothing.

    In addition, whenever you exit a node, after doing the steps above, if current section is not null, associate the node with the section current section.

  5. If the current outlinee is null, then there was no sectioning content element or sectioning root element in the DOM. There is no outline. Abort these steps.

  6. Associate any nodes that were not associated with a section in the steps above with current outlinee as their section.

  7. Associate all nodes with the heading of the section with which they are associated, if any.

  8. If current outlinee is the body element, then the outline created for that element is the outline of the entire document.

The tree of sections created by the algorithm above, or a proper subset thereof, must be used when generating document outlines, for example when generating tables of contents.

When creating an interactive table of contents, entries should jump the user to the relevant sectioning content element, if the section was created for a real element in the original document, or to the relevant heading content element, if the section in the tree was generated for a heading in the above process.

Selecting the first section of the document therefore always takes the user to the top of the document, regardless of where the first heading in the body is to be found.

The outline depth of a heading content element associated with a section section is the number of sections that are ancestors of section in the outline that section finds itself in when the outlines of its Document's elements are created, plus 1. The outline depth of a heading content element not associated with a section is 1.

User agents should provide default headings for sections that do not have explicit section headings.

Consider the following snippet:

<body>
 <nav>
  <p><a href="/">Home</a></p>
 </nav>
 <p>Hello world.</p>
 <aside>
  <p>My cat is cute.</p>
 </aside>
</body>

Although it contains no headings, this snippet has three sections: a document (the body) with two subsections (a nav and an aside). A user agent could present the outline as follows:

  1. Untitled document
    1. Navigation
    2. Sidebar

These default headings ("Untitled document", "Navigation", "Sidebar") are not specified by this specification, and might vary with the user's language, the page's language, the user's preferences, the user agent implementor's preferences, etc.

The following JavaScript function shows how the tree walk could be implemented. The root argument is the root of the tree to walk, and the enter and exit arguments are callbacks that are called with the nodes as they are entered and exited. [ECMA262]

function (root, enter, exit) {
  var node = root;
  start: while (node) {
    enter(node);
    if (node.firstChild) {
      node = node.firstChild;
      continue start;
    }
    while (node) {
      exit(node);
      if (node.nextSibling) {
        node = node.nextSibling;
        continue start;
      }
      if (node == root)
        node = null;
      else
        node = node.parentNode;
    }
  }
}

4.5 Grouping content

Status: Last call for comments

4.5.1 The p element

Status: Last call for comments

Categories
Flow content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
interface HTMLParagraphElement : HTMLElement {};

The p element represents a paragraph.

The following examples are conforming HTML fragments:

<p>The little kitten gently seated himself on a piece of
carpet. Later in his life, this would be referred to as the time the
cat sat on the mat.</p>
<fieldset>
 <legend>Personal information</legend>
 <p>
   <label>Name: <input name="n"></label>
   <label><input name="anon" type="checkbox"> Hide from other users</label>
 </p>
 <p><label>Address: <textarea name="a"></textarea></label></p>
</fieldset>
<p>There was once an example from Femley,<br>
Whose markup was of dubious quality.<br>
The validator complained,<br>
So the author was pained,<br>
To move the error from the markup to the rhyming.</p>

The p element should not be used when a more specific element is more appropriate.

The following example is technically correct:

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

However, it would be better marked-up as:

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

Or:

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

4.5.2 The hr element

Status: Last call for comments

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Empty.
Content attributes:
Global attributes
DOM interface:
interface HTMLHRElement : HTMLElement {};

The hr element represents a paragraph-level thematic break, e.g. a scene change in a story, or a transition to another topic within a section of a reference book.

The following fictional extract from a project manual shows two sections that use the hr element to separate topics within the section.

<section>
 <h1>Communication</h1>
 <p>There are various methods of communication. This section
 covers a few of the important ones used by the project.</p>
 <hr>
 <p>Communication stones seem to come in pairs and have mysterious
 properties:</p>
 <ul>
  <li>They can transfer thoughts in two directions once activated
  if used alone.</li>
  <li>If used with another device, they can transfer one's
  consciousness to another body.</li>
  <li>If both stones are used with another device, the
  consciousnesses switch bodies.</li>
 </ul>
 <hr>
 <p>Radios use the electromagnetic spectrum in the meter range and
 longer.</p>
 <hr>
 <p>Signal flares use the electromagnetic spectrum in the
 nanometer range.</p>
</section>
<section>
 <h1>Food</h1>
 <p>All food at the project is rationed:</p>
 <dl>
  <dt>Potatoes</dt>
  <dd>Two per day</dd>
  <dt>Soup</dt>
  <dd>One bowl per day</dd>
 </dl>
 <hr>
 <p>Cooking is done by the chefs on a set rotation.</p>
</section>

There is no need for an hr element between the sections themselves, since the section elements and the h1 elements imply thematic changes themselves.

The following extract from Pandora's Star by Peter F. Hamilton shows two paragraphs that precede a scene change and the paragraph that follows it. The scene change, represented in the printed book by a gap containing a solitary centered star between the second and third paragraphs, is here represented using the hr element.

<p>Dudley was ninety-two, in his second life, and fast approaching
time for another rejuvenation. Despite his body having the physical
age of a standard fifty-year-old, the prospect of a long degrading
campaign within academia was one he regarded with dread. For a
supposedly advanced civilization, the Intersolar Commonwearth could be
appallingly backward at times, not to mention cruel.</p>
<p><i>Maybe it won't be that bad</i>, he told himself. The lie was
comforting enough to get him through the rest of the night's
shift.</p>
<hr>
<p>The Carlton AllLander drove Dudley home just after dawn. Like the
astronomer, the vehicle was old and worn, but perfectly capable of
doing its job. It had a cheap diesel engine, common enough on a
semi-frontier world like Gralmond, although its drive array was a
thoroughly modern photoneural processor. With its high suspension and
deep-tread tyres it could plough along the dirt track to the
observatory in all weather and seasons, including the metre-deep snow
of Gralmond's winters.</p>

The hr element does not affect the document's outline.

4.5.3 The pre element

Status: Last call for comments

Categories
Flow content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
interface HTMLPreElement : HTMLElement {};

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

In the HTML syntax, a leading newline character immediately following the pre element start tag is stripped.

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

Authors are encouraged to consider how preformatted text will be experienced when the formatting is lost, as will be the case for users of speech synthesizers, braille displays, and the like. For cases like ASCII art, it is likely that an alternative presentation, such as a textual description, would be more universally accessible to the readers of the document.

To represent a block of computer code, the pre element can be used with a code element; to represent a block of computer output the pre element can be used with a samp element. Similarly, the kbd element can be used within a pre element to indicate text that the user is to enter.

In the following snippet, a sample of computer code is presented.

<p>This is the <code>Panel</code> constructor:</p>
<pre><code>function Panel(element, canClose, closeHandler) {
  this.element = element;
  this.canClose = canClose;
  this.closeHandler = function () { if (closeHandler) closeHandler() };
}</code></pre>

In the following snippet, samp and kbd elements are mixed in the contents of a pre element to show a session of Zork I.

<pre><samp>You are in an open field west of a big white house with a boarded
front door.
There is a small mailbox here.

></samp> <kbd>open mailbox</kbd>

<samp>Opening the mailbox reveals:
A leaflet.

></samp></pre>

The following shows a contemporary poem that uses the pre element to preserve its unusual formatting, which forms an intrinsic part of the poem itself.

<pre>                maxling

it is with a          heart
               heavy

that i admit loss of a feline
        so           loved

a friend lost to the
        unknown
                                (night)

~cdr 11dec07</pre>

4.5.4 The blockquote element

Status: Last call for comments

Categories
Flow content.
Sectioning root.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
cite
DOM interface:
interface HTMLQuoteElement : HTMLElement {
           attribute DOMString cite;
};

The HTMLQuoteElement interface is also used by the q element.

The blockquote element represents a section that is quoted from another source.

Content inside a blockquote must be quoted from another source, whose address, if it has one, may be cited in the cite attribute.

If the cite attribute is present, it must be a valid URL potentially surrounded by spaces. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. User agents should allow users to follow such citation links.

The cite IDL attribute must reflect the element's cite content attribute.

This next example shows the use of cite alongside blockquote:

<p>His next piece was the aptly named <cite>Sonnet 130</cite>:</p>
<blockquote cite="http://quotes.example.org/s/sonnet130.html">
  <p>My mistress' eyes are nothing like the sun,<br>
  Coral is far more red, than her lips red,<br>
  ...

This example shows how a forum post could use blockquote to show what post a user is replying to. The article element is used for each post, to mark up the threading.

<article>
 <h1><a href="http://bacon.example.com/?blog=109431">Bacon on a crowbar</a></h1>
 <article>
  <header><strong>t3yw</strong> 12 points 1 hour ago</header>
  <p>I bet a narwhal would love that.</p>
  <footer><a href="?pid=29578">permalink</a></footer>
  <article>
   <header><strong>greg</strong> 8 points 1 hour ago</header>
   <blockquote><p>I bet a narwhal would love that.</p></blockquote>
   <p>Dude narwhals don't eat bacon.</p>
   <footer><a href="?pid=29579">permalink</a></footer>
   <article>
    <header><strong>t3yw</strong> 15 points 1 hour ago</header>
    <blockquote>
     <blockquote><p>I bet a narwhal would love that.</p></blockquote>
     <p>Dude narwhals don't eat bacon.</p>
    </blockquote>
    <p>Next thing you'll be saying they don't get capes and wizard
    hats either!</p>
    <footer><a href="?pid=29580">permalink</a></footer>
    <article>
     <article>
      <header><strong>boing</strong> -5 points 1 hour ago</header>
      <p>narwhals are worse than ceiling cat</p>
      <footer><a href="?pid=29581">permalink</a></footer>
     </article>
    </article>
   </article>
  </article>
  <article>
   <header><strong>fred</strong> 1 points 23 minutes ago</header>
   <blockquote><p>I bet a narwhal would love that.</p></blockquote>
   <p>I bet they'd love to peel a banana too.</p>
   <footer><a href="?pid=29582">permalink</a></footer>
  </article>
 </article>
</article>

Examples of how to represent a conversation are shown in a later section; it is not appropriate to use the cite and blockquote elements for this purpose.

4.5.5 The ol element

Status: Last call for comments

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more li elements.
Content attributes:
Global attributes
reversed
start
DOM interface:
interface HTMLOListElement : HTMLElement {
           attribute boolean reversed;
           attribute long start;
};

The ol element represents a list of items, where the items have been intentionally ordered, such that changing the order would change the meaning of the document.

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

The reversed attribute is a boolean attribute. If present, it indicates that the list is a descending list (..., 3, 2, 1). If the attribute is omitted, the list is an ascending list (1, 2, 3, ...).

The start attribute, if present, must be a valid integer giving the ordinal value of the first list item.

If the start attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. The default value, used if the attribute is missing or if the value cannot be converted to a number according to the referenced algorithm, is 1 if the element has no reversed attribute, and is the number of child li elements otherwise.

The first item in the list has the ordinal value given by the ol element's start attribute, unless that li element has a value attribute with a value that can be successfully parsed, in which case it has the ordinal value given by that value attribute.

Each subsequent item in the list has the ordinal value given by its value attribute, if it has one, or, if it doesn't, the ordinal value of the previous item, plus one if the reversed is absent, or minus one if it is present.

The reversed IDL attribute must reflect the value of the reversed content attribute.

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

The following markup shows a list where the order matters, and where the ol element is therefore appropriate. Compare this list to the equivalent list in the ul section to see an example of the same items using the ul element.

<p>I have lived in the following countries (given in the order of when
I first lived there):</p>
<ol>
 <li>Switzerland
 <li>United Kingdom
 <li>United States
 <li>Norway
</ol>

Note how changing the order of the list changes the meaning of the document. In the following example, changing the relative order of the first two items has changed the birthplace of the author:

<p>I have lived in the following countries (given in the order of when
I first lived there):</p>
<ol>
 <li>United Kingdom
 <li>Switzerland
 <li>United States
 <li>Norway
</ol>

4.5.6 The ul element

Status: Last call for comments

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more li elements.
Content attributes:
Global attributes
DOM interface:
interface HTMLUListElement : HTMLElement {};

The ul element represents a list of items, where the order of the items is not important — that is, where changing the order would not materially change the meaning of the document.

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

The following markup shows a list where the order does not matter, and where the ul element is therefore appropriate. Compare this list to the equivalent list in the ol section to see an example of the same items using the ol element.

<p>I have lived in the following countries:</p>
<ul>
 <li>Norway
 <li>Switzerland
 <li>United Kingdom
 <li>United States
</ul>

Note that changing the order of the list does not change the meaning of the document. The items in the snippet above are given in alphabetical order, but in the snippet below they are given in order of the size of their current account balance in 2007, without changing the meaning of the document whatsoever:

<p>I have lived in the following countries:</p>
<ul>
 <li>Switzerland
 <li>Norway
 <li>United Kingdom
 <li>United States
</ul>

4.5.7 The li element

Status: Last call for comments

Categories
None.
Contexts in which this element may be used:
Inside ol elements.
Inside ul elements.
Inside menu elements.
Content model:
Flow content.
Content attributes:
Global attributes
If the element is a child of an ol element: value
DOM interface:
interface HTMLLIElement : HTMLElement {
           attribute long value;
};

The li element represents a list item. If its parent element is an ol, ul, or menu element, then the element is an item of the parent element's list, as defined for those elements. Otherwise, the list item has no defined list-related relationship to any other li element.

The value attribute, if present, must be a valid integer giving the ordinal value of the list item.

If the value attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. If the attribute's value cannot be converted to a number, the attribute must be treated as if it was absent. The attribute has no default value.

The value attribute is processed relative to the element's parent ol element (q.v.), if there is one. If there is not, the attribute has no effect.

The value IDL attribute must reflect the value of the value content attribute.

The following example, the top ten movies are listed (in reverse order). Note the way the list is given a title by using a figure element and its figcaption element.

<figure>
 <figcaption>The top 10 movies of all time</figcaption>
 <ol>
  <li value="10"><cite>Josie and the Pussycats</cite>, 2001</li>
  <li value="9"><cite lang="sh">Црна мачка, бели мачор</cite>, 1998</li>
  <li value="8"><cite>A Bug's Life</cite>, 1998</li>
  <li value="7"><cite>Toy Story</cite>, 1995</li>
  <li value="6"><cite>Monsters, Inc</cite>, 2001</li>
  <li value="5"><cite>Cars</cite>, 2006</li>
  <li value="4"><cite>Toy Story 2</cite>, 1999</li>
  <li value="3"><cite>Finding Nemo</cite>, 2003</li>
  <li value="2"><cite>The Incredibles</cite>, 2004</li>
  <li value="1"><cite>Ratatouille</cite>, 2007</li>
 </ol>
</figure>

The markup could also be written as follows, using the reversed attribute on the ol element:

<figure>
 <figcaption>The top 10 movies of all time</figcaption>
 <ol reversed>
  <li><cite>Josie and the Pussycats</cite>, 2001</li>
  <li><cite lang="sh">Црна мачка, бели мачор</cite>, 1998</li>
  <li><cite>A Bug's Life</cite>, 1998</li>
  <li><cite>Toy Story</cite>, 1995</li>
  <li><cite>Monsters, Inc</cite>, 2001</li>
  <li><cite>Cars</cite>, 2006</li>
  <li><cite>Toy Story 2</cite>, 1999</li>
  <li><cite>Finding Nemo</cite>, 2003</li>
  <li><cite>The Incredibles</cite>, 2004</li>
  <li><cite>Ratatouille</cite>, 2007</li>
 </ol>
</figure>

If the li element is the child of a menu element and itself has a child that defines a command, then the li element will match the :enabled and :disabled pseudo-classes in the same way as the first such child element does.

4.5.8 The dl element

Status: Last call for comments

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more groups each consisting of one or more dt elements followed by one or more dd elements.
Content attributes:
Global attributes
DOM interface:
interface HTMLDListElement : HTMLElement {};

The dl element represents an association list consisting of zero or more name-value groups (a description list). Each group must consist of one or more names (dt elements) followed by one or more values (dd elements). Within a single dl element, there should not be more than one dt element for each name.

Name-value groups may be terms and definitions, metadata topics and values, or any other groups of name-value data.

The values within a group are alternatives; multiple paragraphs forming part of the same value must all be given within the same dd element.

The order of the list of groups, and of the names and values within each group, may be significant.

If a dl element is empty, it contains no groups.

If a dl element contains non-whitespace text nodes, or elements other than dt and dd, then those elements or text nodes do not form part of any groups in that dl.

If a dl element contains only dt elements, then it consists of one group with names but no values.

If a dl element contains only dd elements, then it consists of one group with values but no names.

If a dl element starts with one or more dd elements, then the first group has no associated name.

If a dl element ends with one or more dt elements, then the last group has no associated value.

When a dl element doesn't match its content model, it is often due to accidentally using dd elements in the place of dt elements and vice versa. Conformance checkers can spot such mistakes and might be able to advise authors how to correctly use the markup.

In the following example, one entry ("Authors") is linked to two values ("John" and "Luke").

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

In the following example, one definition is linked to two terms.

<dl>
 <dt lang="en-US"> <dfn>color</dfn> </dt>
 <dt lang="en-GB"> <dfn>colour</dfn> </dt>
 <dd> A sensation which (in humans) derives from the ability of
 the fine structure of the eye to distinguish three differently
 filtered analyses of a view. </dd>
</dl>

The following example illustrates the use of the dl element to mark up metadata of sorts. At the end of the example, one group has two metadata labels ("Authors" and "Editors") and two values ("Robert Rothman" and "Daniel Jackson").

<dl>
 <dt> Last modified time </dt>
 <dd> 2004-12-23T23:33Z </dd>
 <dt> Recommended update interval </dt>
 <dd> 60s </dd>
 <dt> Authors </dt>
 <dt> Editors </dt>
 <dd> Robert Rothman </dd>
 <dd> Daniel Jackson </dd>
</dl>

The following example shows the dl element used to give a set of instructions. The order of the instructions here is important (in the other examples, the order of the blocks was not important).

<p>Determine the victory points as follows (use the
first matching case):</p>
<dl>
 <dt> If you have exactly five gold coins </dt>
 <dd> You get five victory points </dd>
 <dt> If you have one or more gold coins, and you have one or more silver coins </dt>
 <dd> You get two victory points </dd>
 <dt> If you have one or more silver coins </dt>
 <dd> You get one victory point </dd>
 <dt> Otherwise </dt>
 <dd> You get no victory points </dd>
</dl>

The following snippet shows a dl element being used as a glossary. Note the use of dfn to indicate the word being defined.

<dl>
 <dt><dfn>Apartment</dfn>, n.</dt>
 <dd>An execution context grouping one or more threads with one or
 more COM objects.</dd>
 <dt><dfn>Flat</dfn>, n.</dt>
 <dd>A deflated tire.</dd>
 <dt><dfn>Home</dfn>, n.</dt>
 <dd>The user's login directory.</dd>
</dl>

The dl element is inappropriate for marking up dialogue. Examples of how to mark up dialogue are shown below.

4.5.9 The dt element

Status: Last call for comments

Categories
None.
Contexts in which this element may be used:
Before dd or dt elements inside dl elements.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The dt element represents the term, or name, part of a term-description group in a description list (dl element).

The dt element itself, when used in a dl element, does not indicate that its contents are a term being defined, but this can be indicated using the dfn element.

This example shows a list of frequently asked questions (a FAQ) marked up using the dt element for questions and the dd element for answers.

<article>
 <h1>FAQ</h1>
 <dl>
  <dt>What do we want?</dt>
  <dd>Our data.</dd>
  <dt>When do we want it?</dt>
  <dd>Now.</dd>
  <dt>Where is it?</dt>
  <dd>We are not sure.</dd>
 </dl>
</article>

4.5.10 The dd element

Status: Last call for comments

Categories
None.
Contexts in which this element may be used:
After dt or dd elements inside dl elements.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The dd element represents the description, definition, or value, part of a term-description group in a description list (dl element).

A dl can be used to define a vocabulary list, like in a dictionary. In the following example, each entry, given by a dt with a dfn, has several dds, showing the various parts of the definition.

<dl>
 <dt><dfn>happiness</dfn></dt>
 <dd class="pronunciation">/'hæ p. nes/</dd>
 <dd class="part-of-speech"><i><abbr>n.</abbr></i></dd>
 <dd>The state of being happy.</dd>
 <dd>Good fortune; success. <q>Oh <b>happiness</b>! It worked!</q></dd>
 <dt><dfn>rejoice</dfn></dt>
 <dd class="pronunciation">/ri jois'/</dd>
 <dd><i class="part-of-speech"><abbr>v.intr.</abbr></i> To be delighted oneself.</dd>
 <dd><i class="part-of-speech"><abbr>v.tr.</abbr></i> To cause one to be delighted.</dd>
</dl>

4.5.11 The figure element

Status: Last call for comments

Categories
Flow content.
Sectioning root.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Either: One figcaption element followed by flow content.
Or: Flow content followed by one figcaption element.
Or: Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The figure element represents some flow content, optionally with a caption, that is self-contained and is typically referenced as a single unit from the main flow of the document.

The element can thus be used to annotate illustrations, diagrams, photos, code listings, etc, that are referred to from the main content of the document, but that could, without affecting the flow of the document, be moved away from that primary content, e.g. to the side of the page, to dedicated pages, or to an appendix.

The first figcaption element child of the element, if any, represents the caption of the figure element's contents. If there is no child figcaption element, then there is no caption.

This example shows the figure element to mark up a code listing.

<p>In <a href="#l4">listing 4</a> we see the primary core interface
API declaration.</p>
<figure id="l4">
 <figcaption>Listing 4. The primary core interface API declaration.</figcaption>
 <pre><code>interface PrimaryCore {
 boolean verifyDataLine();
 void sendData(in sequence&lt;byte> data);
 void initSelfDestruct();
}</code></pre>
</figure>
<p>The API is designed to use UTF-8.</p>

Here we see a figure element to mark up a photo.

<figure>
 <img src="bubbles-work.jpeg"
      alt="Bubbles, sitting in his office chair, works on his
           latest project intently.">
 <figcaption>Bubbles at work</figcaption>
</figure>

In this example, we see an image that is not a figure, as well as an image and a video that are.

<h2>Malinko's comics</h2>

<p>This case centered on some sort of "intellectual property"
infringement related to a comic (see Exhibit A). The suit started
after a trailer ending with these words:

<blockquote>
 <img src="promblem-packed-action.png" alt="ROUGH COPY! Promblem-Packed Action!">
</blockquote>

<p>...was aired. A lawyer, armed with a Bigger Notebook, launched a
preemptive strike using snowballs. A complete copy of the trailer is
included with Exhibit B.

<figure>
 <img src="ex-a.png" alt="Two squiggles on a dirty piece of paper.">
 <figcaption>Exhibit A. The alleged <cite>rough copy</cite> comic.</figcaption>
</figure>

<figure>
 <video src="ex-b.mov"></video>
 <figcaption>Exhibit B. The <cite>Rough Copy</cite> trailer.</figcaption>
</figure>

<p>The case was resolved out of court.

Here, a part of a poem is marked up using figure.

<figure>
 <p>'Twas brillig, and the slithy toves<br>
 Did gyre and gimble in the wabe;<br>
 All mimsy were the borogoves,<br>
 And the mome raths outgrabe.</p>
 <figcaption><cite>Jabberwocky</cite> (first verse). Lewis Carroll, 1832-98</figcaption>
</figure>

In this example, which could be part of a much larger work discussing a castle, the figure has three images in it.

<figure>
 <img src="castle1423.jpeg" title="Etching. Anonymous, ca. 1423."
      alt="The castle has one tower, and a tall wall around it.">
 <img src="castle1858.jpeg" title="Oil-based paint on canvas. Maria Towle, 1858."
      alt="The castle now has two towers and two walls.">
 <img src="castle1999.jpeg" title="Film photograph. Peter Jankle, 1999."
      alt="The castle lies in ruins, the original tower all that remains in one piece.">
 <figcaption>The castle through the ages: 1423, 1858, and 1999 respectively.</figcaption>
</figure>

4.5.12 The figcaption element

Categories
None.
Contexts in which this element may be used:
As the first or last child of a figure element.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The figcaption element represents a caption or legend for the rest of the contents of the figcaption element's parent figure element, if any.

4.5.13 The div element

Status: Last call for comments

Categories
Flow content.
formatBlock candidate.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Content attributes:
Global attributes
DOM interface:
interface HTMLDivElement : HTMLElement {};

The div element has no special meaning at all. It represents its children. It can be used with the class, lang, and title attributes to mark up semantics common to a group of consecutive elements.

Authors are strongly encouraged to view the div element as an element of last resort, for when no other element is suitable. Use of the div element instead of more appropriate elements leads to poor accessibility for readers and poor maintainability for authors.

For example, a blog post would be marked up using article, a chapter using section, a page's navigation aids using nav, and a group of form controls using fieldset.

On the other hand, div elements can be useful for stylistic purposes or to wrap multiple paragraphs within a section that are all to be annotated in a similar way. In the following example, we see div elements used as a way to set the language of two paragraphs at once, instead of setting the language on the two paragraph elements separately:

<article lang="en-US">
 <h1>My use of language and my cats</h1>
 <p>My cat's behavior hasn't changed much since her absence, except
 that she plays her new physique to the neighbors regularly, in an
 attempt to get pets.</p>
 <div lang="en-GB">
  <p>My other cat, coloured black and white, is a sweetie. He followed
  us to the pool today, walking down the pavement with us. Yesterday
  he apparently visited our neighbours. I wonder if he recognises that
  their flat is a mirror image of ours.</p>
  <p>Hm, I just noticed that in the last paragraph I used British
  English. But I'm supposed to write in American English. So I
  shouldn't say "pavement" or "flat" or "colour"...</p>
 </div>
 <p>I should say "sidewalk" and "apartment" and "color"!</p>
</article>

4.6 Text-level semantics

Status: Last call for comments

4.6.1 The a element

Status: Last call for comments

Categories
Flow content.
When the element only contains phrasing content: phrasing content.
Interactive content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Transparent, but there must be no interactive content descendant.
Content attributes:
Global attributes
href
target
rel
media
hreflang
type
DOM interface:
interface HTMLAnchorElement : HTMLElement {
  stringifier attribute DOMString href;
           attribute DOMString target;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;

           attribute DOMString text;

  // URL decomposition IDL attributes
           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;
};

If the a element has an href attribute, then it represents a hyperlink (a hypertext anchor).

If the a element has no href attribute, then the element represents a placeholder for where a link might otherwise have been placed, if it had been relevant.

The target, rel, media, hreflang, and type attributes must be omitted if the href attribute is not present.

If a site uses a consistent navigation toolbar on every page, then the link that would normally link to the page itself could be marked up using an a element:

<nav>
 <ul>
  <li> <a href="/">Home</a> </li>
  <li> <a href="/news">News</a> </li>
  <li> <a>Examples</a> </li>
  <li> <a href="/legal">Legal</a> </li>
 </ul>
</nav>

The href, target attributes affect what happens when users follow hyperlinks created using the a element. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

The activation behavior of a elements that represent hyperlinks is to run the following steps:

  1. If the DOMActivate event in question is not trusted (i.e. a click() method call was the reason for the event being dispatched), and the a element's target attribute is such that applying the rules for choosing a browsing context given a browsing context name, using the value of the target attribute as the browsing context name, would result in there not being a chosen browsing context, then raise an INVALID_ACCESS_ERR exception and abort these steps.

  2. If the target of the click event is an img element with an ismap attribute specified, then server-side image map processing must be performed, as follows:

    1. If the DOMActivate event was dispatched as the result of a real pointing-device-triggered click event on the img element, then let x be the distance in CSS pixels from the left edge of the image's left border, if it has one, or the left edge of the image otherwise, to the location of the click, and let y be the distance in CSS pixels from the top edge of the image's top border, if it has one, or the top edge of the image otherwise, to the location of the click. Otherwise, let x and y be zero.
    2. Let the hyperlink suffix be a U+003F QUESTION MARK character, the value of x expressed as a base-ten integer using ASCII digits, a U+002C COMMA character (,), and the value of y expressed as a base-ten integer using ASCII digits. ASCII digits are the characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).
  3. Finally, the user agent must follow the hyperlink defined by the a element. If the steps above defined a hyperlink suffix, then take that into account when following the hyperlink.

a . text

Same as textContent.

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

The IDL attribute relList must reflect the rel content attribute.

The text IDL attribute, on getting, must return the same value as the textContent IDL attribute on the element, and on setting, must act as if the textContent IDL attribute on the element had been set to the new value.

The a element also supports the complement of URL decomposition IDL attributes, protocol, host, port, hostname, pathname, search, and hash. These must follow the rules given for URL decomposition IDL attributes, with the input being the result of resolving the element's href attribute relative to the element, if there is such an attribute and resolving it is successful, or the empty string otherwise; and the common setter action being the same as setting the element's href attribute to the new output value.

The a element may be wrapped around entire paragraphs, lists, tables, and so forth, even entire sections, so long as there is no interactive content within (e.g. buttons or other links). This example shows how this can be used to make an entire advertising block into a link:

<aside class="advertising">
 <h1>Advertising</h1>
 <a href="http://ad.example.com/?adid=1929&amp;pubid=1422">
  <section>
   <h1>Mellblomatic 9000!</h1>
   <p>Turn all your widgets into mellbloms!</p>
   <p>Only $9.99 plus shipping and handling.</p>
  </section>
 </a>
 <a href="http://ad.example.com/?adid=375&amp;pubid=1422">
  <section>
   <h1>The Mellblom Browser</h1>
   <p>Web browsing at the speed of light.</p>
   <p>No other browser goes faster!</p>
  </section>
 </a>
</aside>

4.6.2 The em element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The em element represents stress emphasis of its contents.

The level of emphasis that a particular piece of content has is given by its number of ancestor em elements.

The placement of emphasis changes the meaning of the sentence. The element thus forms an integral part of the content. The precise way in which emphasis is used in this way depends on the language.

These examples show how changing the emphasis changes the meaning. First, a general statement of fact, with no emphasis:

<p>Cats are cute animals.</p>

By emphasizing the first word, the statement implies that the kind of animal under discussion is in question (maybe someone is asserting that dogs are cute):

<p><em>Cats</em> are cute animals.</p>

Moving the emphasis to the verb, one highlights that the truth of the entire sentence is in question (maybe someone is saying cats are not cute):

<p>Cats <em>are</em> cute animals.</p>

By moving it to the adjective, the exact nature of the cats is reasserted (maybe someone suggested cats were mean animals):

<p>Cats are <em>cute</em> animals.</p>

Similarly, if someone asserted that cats were vegetables, someone correcting this might emphasize the last word:

<p>Cats are cute <em>animals</em>.</p>

By emphasizing the entire sentence, it becomes clear that the speaker is fighting hard to get the point across. This kind of emphasis also typically affects the punctuation, hence the exclamation mark here.

<p><em>Cats are cute animals!</em></p>

Anger mixed with emphasizing the cuteness could lead to markup such as:

<p><em>Cats are <em>cute</em> animals!</em></p>

The em element isn't a generic "italics" element. Sometimes, text is intended to stand out from the rest of the paragraph, as if it was in a different mood or voice. For this, the i element is more appropriate.

The em element also isn't intended to convey importance; for that purpose, the strong element is more appropriate.

4.6.3 The strong element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The strong element represents strong importance for its contents.

The relative level of importance of a piece of content is given by its number of ancestor strong elements; each strong element increases the importance of its contents.

Changing the importance of a piece of text with the strong element does not change the meaning of the sentence.

Here is an example of a warning notice in a game, with the various parts marked up according to how important they are:

<p><strong>Warning.</strong> This dungeon is dangerous.
<strong>Avoid the ducks.</strong> Take any gold you find.
<strong><strong>Do not take any of the diamonds</strong>,
they are explosive and <strong>will destroy anything within
ten meters.</strong></strong> You have been warned.</p>

4.6.4 The small element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The small element represents side comments such as small print.

Small print typically features disclaimers, caveats, legal restrictions, or copyrights. Small print is also sometimes used for attribution, or for satisfying licensing requirements.

The small element does not "de-emphasize" or lower the importance of text emphasized by the em element or marked as important with the strong element. To mark text as not emphasized or important, simply do not mark it up with the em or strong elements respectively.

The small element should not be used for extended spans of text, such as multiple paragraphs, lists, or sections of text. It is only intended for short runs of text. The text of a page listing terms of use, for instance, would not be a suitable candidate for the small element: in such a case, the text is not a side comment, it is the main content of the page.

In this example the footer contains contact information and a copyright notice.

<footer>
 <address>
  For more details, contact
  <a href="mailto:js@example.com">John Smith</a>.
 </address>
 <p><small>© copyright 2038 Example Corp.</small></p>
</footer>

In this second example, the small element is used for a side comment in an article.

<p>Example Corp today announced record profits for the
second quarter <small>(Full Disclosure: Foo News is a subsidiary of
Example Corp)</small>, leading to speculation about a third quarter
merger with Demo Group.</p>

This is distinct from a sidebar, which might be multiple paragraphs long and is removed from the main flow of text. In the following example, we see a sidebar from the same article. This sidebar also has small print, indicating the source of the information in the sidebar.

<aside>
 <h1>Example Corp</h1>
 <p>This company mostly creates small software and Web
 sites.</p>
 <p>The Example Corp company mission is "To provide entertainment
 and news on a sample basis".</p>
 <p><small>Information obtained from <a
 href="http://example.com/about.html">example.com</a> home
 page.</small></p>
</aside>

In this last example, the small element is marked as being important small print.

<p><strong><small>Continued use of this service will result in a kiss.</small></strong></p>

4.6.5 The cite element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The cite element represents the title of a work (e.g. a book, a paper, an essay, a poem, a score, a song, a script, a film, a TV show, a game, a sculpture, a painting, a theatre production, a play, an opera, a musical, an exhibition, a legal case report, etc). This can be a work that is being quoted or referenced in detail (i.e. a citation), or it can just be a work that is mentioned in passing.

A person's name is not the title of a work — even if people call that person a piece of work — and the element must therefore not be used to mark up people's names. (In some cases, the b element might be appropriate for names; e.g. in a gossip article where the names of famous people are keywords rendered with a different style to draw attention to them. In other cases, if an element is really needed, the span element can be used.)

This next example shows a typical use of the cite element:

<p>My favorite book is <cite>The Reality Dysfunction</cite> by
Peter F. Hamilton. My favorite comic is <cite>Pearls Before
Swine</cite> by Stephan Pastis. My favorite track is <cite>Jive
Samba</cite> by the Cannonball Adderley Sextet.</p>

This is correct usage:

<p>According to the Wikipedia article <cite>HTML</cite>, as it
stood in mid-February 2008, leaving attribute values unquoted is
unsafe. This is obviously an over-simplification.</p>

The following, however, is incorrect usage, as the cite element here is containing far more than the title of the work:

<!-- do not copy this example, it is an example of bad usage! -->
<p>According to <cite>the Wikipedia article on HTML</cite>, as it
stood in mid-February 2008, leaving attribute values unquoted is
unsafe. This is obviously an over-simplification.</p>

The cite element is obviously a key part of any citation in a bibliography, but it is only used to mark the title:

<p><cite>Universal Declaration of Human Rights</cite>, United Nations,
December 1948. Adopted by General Assembly resolution 217 A (III).</p>

A citation is not a quote (for which the q element is appropriate).

This is incorrect usage, because cite is not for quotes:

<p><cite>This is wrong!</cite>, said Ian.</p>

This is also incorrect usage, because a person is not a work:

<p><q>This is still wrong!</q>, said <cite>Ian</cite>.</p>

The correct usage does not use a cite element:

<p><q>This is correct</q>, said Ian.</p>

As mentioned above, the b element might be relevant for marking names as being keywords in certain kinds of documents:

<p>And then <b>Ian</b> said <q>this might be right, in a
gossip column, maybe!</q>.</p>

4.6.6 The q element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
cite
DOM interface:
Uses HTMLQuoteElement.

The q element represents some phrasing content quoted from another source.

Quotation punctuation (such as quotation marks) that is quoting the contents of the element must not appear immediately before, after, or inside q elements; they will be inserted into the rendering by the user agent.

Content inside a q element must be quoted from another source, whose address, if it has one, may be cited in the cite attribute. The source may be fictional, as when quoting characters in a novel or screenplay.

If the cite attribute is present, it must be a valid URL potentially surrounded by spaces. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. User agents should allow users to follow such citation links.

The q element must not be used in place of quotation marks that do not represent quotes; for example, it is inappropriate to use the q element for marking up sarcastic statements.

The use of q elements to mark up quotations is entirely optional; using explicit quotation punctuation without q elements is just as correct.

Here is a simple example of the use of the q element:

<p>The man said <q>Things that are impossible just take
longer</q>. I disagreed with him.</p>

Here is an example with both an explicit citation link in the q element, and an explicit citation outside:

<p>The W3C page <cite>About W3C</cite> says the W3C's
mission is <q cite="http://www.w3.org/Consortium/">To lead the
World Wide Web to its full potential by developing protocols and
guidelines that ensure long-term growth for the Web</q>. I
disagree with this mission.</p>

In the following example, the quotation itself contains a quotation:

<p>In <cite>Example One</cite>, he writes <q>The man
said <q>Things that are impossible just take longer</q>. I
disagreed with him</q>. Well, I disagree even more!</p>

In the following example, quotation marks are used instead of the q element:

<p>His best argument was ❝I disagree❞, which
I thought was laughable.</p>

In the following example, there is no quote — the quotation marks are used to name a word. Use of the q element in this case would be inappropriate.

<p>The word "ineffable" could have been used to describe the disaster
resulting from the campaign's mismanagement.</p>

4.6.7 The dfn element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content, but there must be no dfn element descendants.
Content attributes:
Global attributes
Also, the title attribute has special semantics on this element.
DOM interface:
Uses HTMLElement.

The dfn element represents the defining instance of a term. The paragraph, description list group, or section that is the nearest ancestor of the dfn element must also contain the definition(s) for the term given by the dfn element.

Defining term: If the dfn element has a title attribute, then the exact value of that attribute is the term being defined. Otherwise, if it contains exactly one element child node and no child text nodes, and that child element is an abbr element with a title attribute, then the exact value of that attribute is the term being defined. Otherwise, it is the exact textContent of the dfn element that gives the term being defined.

If the title attribute of the dfn element is present, then it must contain only the term being defined.

The title attribute of ancestor elements does not affect dfn elements.

An a element that links to a dfn element represents an instance of the term defined by the dfn element.

In the following fragment, the term "GDO" is first defined in the first paragraph, then used in the second.

<p>The <dfn><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <abbr title="Garage Door Opener">GDO</abbr>
and so Hammond ordered the iris to be opened.</p>

With the addition of an a element, the reference can be made explicit:

<p>The <dfn id=gdo><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <a href=#gdo><abbr title="Garage Door Opener">GDO</abbr></a>
and so Hammond ordered the iris to be opened.</p>

4.6.8 The abbr element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
Also, the title attribute has special semantics on this element.
DOM interface:
Uses HTMLElement.

The abbr element represents an abbreviation or acronym, optionally with its expansion. The title attribute may be used to provide an expansion of the abbreviation. The attribute, if specified, must contain an expansion of the abbreviation, and nothing else.

The paragraph below contains an abbreviation marked up with the abbr element. This paragraph defines the term "Web Hypertext Application Technology Working Group".

<p>The <dfn id=whatwg><abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr></dfn>
is a loose unofficial collaboration of Web browser manufacturers and
interested parties who wish to develop new technologies designed to
allow authors to write and deploy Applications over the World Wide
Web.</p>

An alternative way to write this would be:

<p>The <dfn id=whatwg>Web Hypertext Application Technology
Working Group</dfn> (<abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr>)
is a loose unofficial collaboration of Web browser manufacturers and
interested parties who wish to develop new technologies designed to
allow authors to write and deploy Applications over the World Wide
Web.</p>

This paragraph has two abbreviations. Notice how only one is defined; the other, with no expansion associated with it, does not use the abbr element.

<p>The
<abbr title="Web Hypertext Application Technology Working Group">WHATWG</abbr>
started working on HTML5 in 2004.</p>

This paragraph links an abbreviation to its definition.

<p>The <a href="#whatwg"><abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr></a>
community does not have much representation from Asia.</p>

This paragraph marks up an abbreviation without giving an expansion, possibly as a hook to apply styles for abbreviations (e.g. smallcaps).

<p>Philip` and Dashiva both denied that they were going to
get the issue counts from past revisions of the specification to
backfill the <abbr>WHATWG</abbr> issue graph.</p>

If an abbreviation is pluralized, the expansion's grammatical number (plural vs singular) must match the grammatical number of the contents of the element.

Here the plural is outside the element, so the expansion is in the singular:

<p>Two <abbr title="Working Group">WG</abbr>s worked on
this specification: the <abbr>WHATWG</abbr> and the
<abbr>HTMLWG</abbr>.</p>

Here the plural is inside the element, so the expansion is in the plural:

<p>Two <abbr title="Working Groups">WGs</abbr> worked on
this specification: the <abbr>WHATWG</abbr> and the
<abbr>HTMLWG</abbr>.</p>

Abbreviations do not have to be marked up using this element. It is expected to be useful in the following cases:

Providing an expansion in a title attribute once will not necessarily cause other abbr elements in the same document with the same contents but without a title attribute to behave as if they had the same expansion. Every abbr element is independent.

4.6.9 The time element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content, but there must be no time element descendants.
Content attributes:
Global attributes
datetime
pubdate
DOM interface:
interface HTMLTimeElement : HTMLElement {
           attribute DOMString dateTime;
           attribute boolean pubDate;
  readonly attribute Date valueAsDate;
};

The time element represents either a time on a 24 hour clock, or a precise date in the proleptic Gregorian calendar, optionally with a time and a time-zone offset. [GREGORIAN]

This element is intended as a way to encode modern dates and times in a machine-readable way so that, for example, user agents can offer to add birthday reminders or scheduled events to the user's calendar.

The time element is not intended for encoding times for which a precise date or time cannot be established. For example, it would be inappropriate for encoding times like "one millisecond after the big bang", "the early part of the Jurassic period", or "a winter around 250 BCE".

For dates before the introduction of the Gregorian calendar, authors are encouraged to not use the time element, or else to be very careful about converting dates and times from the period to the Gregorian calendar. This is complicated by the manner in which the Gregorian calendar was phased in, which occurred at different times in different countries, ranging from partway through the 16th century all the way to early in the 20th.

The pubdate attribute is a boolean attribute. If specified, it indicates that the date and time given by the element is the publication date and time of the nearest ancestor article element, or, if the element has no ancestor article element, of the document as a whole. If the element has a pubdate attribute specified, then the element needs a date. For each article element, there must no more than one time element with a pubdate attribute whose nearest ancestor is that article element. Furthermore, for each Document, there must be no more than one time element with a pubdate attribute that does not have an ancestor article element.

The datetime attribute, if present, gives the date or time being specified. Otherwise, the date or time is given by the element's contents.

If the element needs a date, and the datetime attribute is present, then the attribute's value must be a valid date string with optional time.

If the element needs a date, but the datetime attribute is not present, then the element's textContent must be a valid date string in content with optional time.

If the element does not need a date, and the datetime attribute is present, then the attribute's value must be a valid date or time string.

If the element does not need a date, but the datetime attribute is not present, then the element's textContent must be a valid date or time string in content.

The date, if any, must be expressed using the Gregorian calendar.

If the datetime attribute is present, the user agent should convey the attribute's value to the user when rendering the element.

The time element can be used to encode dates, for example in Microformats. The following shows a hypothetical way of encoding an event using a variant on hCalendar that uses the time element:

<div class="vevent">
 <a class="url" href="http://www.web2con.com/">http://www.web2con.com/</a>
  <span class="summary">Web 2.0 Conference</span>:
  <time class="dtstart" datetime="2007-10-05">October 5</time> -
  <time class="dtend" datetime="2007-10-20">19</time>,
  at the <span class="location">Argent Hotel, San Francisco, CA</span>
 </div>

(The end date is encoded as one day after the last date of the event because in the iCalendar format, end dates are exclusive, not inclusive.)

The time element is not necessary for encoding dates or times. In the following snippet, the time is encoded using time, so that it can be restyled (e.g. using XBL2) to match local conventions, while the year is not marked up at all, since marking it up would not be particularly useful.

<p>I usually have a snack at <time>16:00</time>.</p>
<p>I've liked model trains since at least 1983.</p>

Using a styling technology that supports restyling times, the first paragraph from the above snippet could be rendered as follows:

I usually have a snack at 4pm.

Or it could be rendered as follows:

I usually have a snack at 16h00.

The dateTime IDL attribute must reflect the datetime content attribute.

The pubDate IDL attribute must reflect the pubdate content attribute.

User agents, to obtain the date, time, and time-zone offset represented by a time element, must follow these steps:

  1. If the datetime attribute is present, then use the rules to parse a date or time string with the flag in attribute from the value of that attribute, and let the result be result.
  2. Otherwise, use the rules to parse a date or time string with the flag in content from the element's textContent, and let the result be result.
  3. If result is empty (because the parsing failed), then the date is unknown, the time is unknown, and the time-zone offset is unknown.
  4. Otherwise: if result contains a date, then that is the date; if result contains a time, then that is the time; and if result contains a time-zone offset, then the time-zone offset is the element's time-zone offset. (A time-zone offset can only be present if both a date and a time are also present.)
time . valueAsDate

Returns a Date object representing the specified date and time.

The valueAsDate IDL attribute must return either null or a new Date object initialised to the relevant value as defined by the following list:

If the date is known but the time is not
The time corresponding to midnight UTC (i.e. the first second) of the given date.
If the time is known but the date is not
The time corresponding to the given time of 1970-01-01, with the time zone UTC.
If both the date and the time are known
The time corresponding to the date and time, with the given time-zone offset.
If neither the date nor the time are known
The null value.

When a Date object is to be returned, a new one must be constructed.

In the following snippet:

<p>Our first date was <time datetime="2006-09-23">a Saturday</time>.</p>

...the time element's valueAsDate attribute would have the value 1,158,969,600,000ms.

In the following snippet:

<p>Many people get up at <time>08:00</time>.</p>

...the time element's valueAsDate attribute would have the value 28,800,000ms.

In this example, an article's publication date is marked up using time:

<article>
 <h1>Small tasks</h1>
 <footer>Published <time pubdate>2009-08-30</time>.</footer>
 <p>I put a bike bell on his bike.</p>
</article>

Here is another way that could be marked up. In this example, legacy user agents would say "today", while newer user agents would render the time in a locale-specific manner based on the value of the attribute.

<article>
 <h1>Small tasks</h1>
 <footer>Published <time pubdate datetime="2009-08-30">today</time>.</footer>
 <p>I put a bike bell on his bike.</p>
</article>

Here is the same thing but with the time included only. Because the element is empty, legacy user agents will not show anything useful; user agents that implement this specification, on the other hand, would show the date and time in a locale-specific manner.

<article>
 <h1>Small tasks</h1>
 <footer>Published <time pubdate datetime="2009-08-30T07:13Z"></time>.</footer>
 <p>I put a bike bell on his bike.</p>
</article>

4.6.10 The code element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The code element represents a fragment of computer code. This could be an XML element name, a filename, a computer program, or any other string that a computer would recognize.

Although there is no formal way to indicate the language of computer code being marked up, authors who wish to mark code elements with the language used, e.g. so that syntax highlighting scripts can use the right rules, may do so by adding a class prefixed with "language-" to the element.

The following example shows how the element can be used in a paragraph to mark up element names and computer code, including punctuation.

<p>The <code>code</code> element represents a fragment of computer
code.</p>

<p>When you call the <code>activate()</code> method on the
<code>robotSnowman</code> object, the eyes glow.</p>

<p>The example below uses the <code>begin</code> keyword to indicate
the start of a statement block. It is paired with an <code>end</code>
keyword, which is followed by the <code>.</code> punctuation character
(full stop) to indicate the end of the program.</p>

The following example shows how a block of code could be marked up using the pre and code elements.

<pre><code class="language-pascal">var i: Integer;
begin
   i := 1;
end.</code></pre>

A class is used in that example to indicate the language used.

See the pre element for more details.

4.6.11 The var element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The var element represents a variable. This could be an actual variable in a mathematical expression or programming context, or it could just be a term used as a placeholder in prose.

In the paragraph below, the letter "n" is being used as a variable in prose:

<p>If there are <var>n</var> pipes leading to the ice
cream factory then I expect at <em>least</em> <var>n</var>
flavors of ice cream to be available for purchase!</p>

For mathematics, in particular for anything beyond the simplest of expressions, MathML is more appropriate. However, the var element can still be used to refer to specific variables that are then mentioned in MathML expressions.

In this example, an equation is shown, with a legend that references the variables in the equation. The expression itself is marked up with MathML, but the variables are mentioned in the figure's legend using var.

<figure>
 <math>
  <mi>a</mi>
  <mo>=</mo>
  <msqrt>
   <msup><mi>b</mi><mn>2</mn></msup>
   <mi>+</mi>
   <msup><mi>c</mi><mn>2</mn></msup>
  </msqrt>
 </math>
 <figcaption>
  Using Pythagoras' theorem to solve for the hypotenuse <var>a</var> of
  a triangle with sides <var>b</var> and <var>c</var>
 </figcaption>
</figure>

4.6.12 The samp element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The samp element represents (sample) output from a program or computing system.

See the pre and kbd elements for more details.

This example shows the samp element being used inline:

<p>The computer said <samp>Too much cheese in tray
two</samp> but I didn't know what that meant.</p>

This second example shows a block of sample output. Nested samp and kbd elements allow for the styling of specific elements of the sample output using a style sheet.

<pre><samp><span class="prompt">jdoe@mowmow:~$</span> <kbd>ssh demo.example.com</kbd>
Last login: Tue Apr 12 09:10:17 2005 from mowmow.example.com on pts/1
Linux demo 2.6.10-grsec+gg3+e+fhs6b+nfs+gr0501+++p3+c4a+gr2b-reslog-v6.189 #1 SMP Tue Feb 1 11:22:36 PST 2005 i686 unknown

<span class="prompt">jdoe@demo:~$</span> <span class="cursor">_</span></samp></pre>

4.6.13 The kbd element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The kbd element represents user input (typically keyboard input, although it may also be used to represent other input, such as voice commands).

When the kbd element is nested inside a samp element, it represents the input as it was echoed by the system.

When the kbd element contains a samp element, it represents input based on system output, for example invoking a menu item.

When the kbd element is nested inside another kbd element, it represents an actual key or other single unit of input as appropriate for the input mechanism.

Here the kbd element is used to indicate keys to press:

<p>To make George eat an apple, press <kbd><kbd>Shift</kbd>+<kbd>F3</kbd></kbd></p>

In this second example, the user is told to pick a particular menu item. The outer kbd element marks up a block of input, with the inner kbd elements representing each individual step of the input, and the samp elements inside them indicating that the steps are input based on something being displayed by the system, in this case menu labels:

<p>To make George eat an apple, select
    <kbd><kbd><samp>File</samp></kbd>|<kbd><samp>Eat Apple...</samp></kbd></kbd>
</p>

Such precision isn't necessary; the following is equally fine:

<p>To make George eat an apple, select <kbd>File | Eat Apple...</kbd></p>

4.6.14 The sub and sup elements

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which these elements may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Use HTMLElement.

The sup element represents a superscript and the sub element represents a subscript.

These elements must be used only to mark up typographical conventions with specific meanings, not for typographical presentation for presentation's sake. For example, it would be inappropriate for the sub and sup elements to be used in the name of the LaTeX document preparation system. In general, authors should use these elements only if the absence of those elements would change the meaning of the content.

In certain languages, superscripts are part of the typographical conventions for some abbreviations.

<p>The most beautiful women are
<span lang="fr"><abbr>M<sup>lle</sup></abbr> Gwendoline</span> and
<span lang="fr"><abbr>M<sup>me</sup></abbr> Denise</span>.</p>

The sub element can be used inside a var element, for variables that have subscripts.

Here, the sub element is used to represents the subscript that identifies the variable in a family of variables:

<p>The coordinate of the <var>i</var>th point is
(<var>x<sub><var>i</var></sub></var>, <var>y<sub><var>i</var></sub></var>).
For example, the 10th point has coordinate
(<var>x<sub>10</sub></var>, <var>y<sub>10</sub></var>).</p>

Mathematical expressions often use subscripts and superscripts. Authors are encouraged to use MathML for marking up mathematics, but authors may opt to use sub and sup if detailed mathematical markup is not desired. [MATHML]

<var>E</var>=<var>m</var><var>c</var><sup>2</sup>
f(<var>x</var>, <var>n</var>) = log<sub>4</sub><var>x</var><sup><var>n</var></sup>

4.6.15 The i element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Content attributes:
Global attributes
DOM interface:
Uses HTMLElement.

The i element represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, a ship name, or some other prose whose typical typographic presentation is italicized.

Terms in languages different from the main text should be annotated with lang attributes (or, in XML, lang attributes in the XML namespace).

The examples below show uses of the i element:

<p>The <i class="taxonomy">Felis silvestris catus</i> is cute.</p>
<p>The term <i>prose content</i> is defined above.</p>
<p>There is a certain <i lang="fr">je ne sais quoi</i> in the air.</p>

In the following example, a dream sequence is marked up using i elements.

<p>Raymond tried to sleep.</p>
<p><i>The ship sailed away on Thursday</i>, he
dreamt. <i>The ship had many people aboard, including a beautiful
princess called Carey. He watched her, day-in, day-out, hoping she
would notice him, but she never did.</i></p>
<p><i>Finally one night he picked up the courage to speak with
her—</i></p>
<p>Raymond woke with a start as the fire alarm rang out.</p>

Authors are encouraged to use the class attribute on the i element to identify why the element is being used, so that if the style of a particular use (e.g. dream sequences as opposed to taxonomic terms) is to be changed at a later date, the author doesn't have to go through the entire document (or series of related documents) annotating each use. Similarly, authors are encouraged to consider whether other elements might be more applicable than the i element, for instance the em element for marking up stress emphasis, or the dfn element to mark up the defining instance of a term.

Style sheets can be used to format i elements, just like any other element can be restyled. Thus, it is not the case that content in i elements will necessarily be italicized.

4.6.16 The b element

Status: Last call for comments

Categories
Flow content.
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model: