[meta] Comply with WCAG guideline 4.1: Compatibility

WCAG Guideline 4.1:

Maximize compatibility with current and future user agents, including assistive technologies.

4.1.1 Parsing:

In content implemented using markup languages, elements have complete start and end tags, elements are nested according to their specifications, elements do not contain duplicate attributes, and any IDs are unique, except where the specifications allow these features. (Level A)

Sufficient HTML-techniques:

• G134: Validating Web pages

#1333730: [Meta] PHP DOM (libxml2) only understands XHTML4, misinterprets HTML5, but D8 must cope with HTML5

• G192: Fully conforming to specifications
• H88: Using HTML according to spec
• Ensuring that Web pages can be parsed by using one of the following techniques:
  • H74: Ensuring that opening and closing tags are used according to specification AND
    H93: Ensuring that id attributes are unique on a Web page AND
    H94: Ensuring that elements do not contain duplicate attributes

  #1734716: File field form label has incorrect id in @for attribute

  • H75: Ensuring that Web pages are well-formed

Reference:

• http://www.w3.org/WAI/GL/UNDERSTANDING-WCAG20/ensure-compat-parses.html

4.1.2 Name, Role, Value:

For all user interface components (including but not limited to: form elements, links and components generated by scripts), the name and role can be programmatically determined; states, properties, and values that can be set by the user can be programmatically set; and notification of changes to these items is available to user agents, including assistive technologies. (Level A)

Sufficient HTML-techniques:

• G108: Using markup features to expose the name and role, allow user-settable properties to be directly set, and provide notification of changes using technology-specific techniques below:
  • H91: Using HTML form controls and links
  • H44: Using label elements to associate text labels with form controls

  #933004: Test that all form elements have a title for accessibility

  • H64: Using the title attribute of the frame and iframe elements

  We don't use frames or iframes in core.

  • H65: Using the title attribute to identify form controls when the label element cannot be used

  #933004: Test that all form elements have a title for accessibility

  • H88: Using HTML according to spec

Reference:

• http://www.w3.org/WAI/GL/UNDERSTANDING-WCAG20/ensure-compat-rsv.html

See also:

• http://www.w3.org/WAI/GL/WCAG20/#ensure-compat