See Understanding Techniques for WCAG Success Criteria for important information about the usage of these informative techniques and how they relate to the normative WCAG 2.0 success criteria. The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.0.
Applies to the Document Object Model (DOM) for XML.
This failure relates to:
Editorial Note: Comment LC-2861 pointed out the two failure conditions are pretty separate. We might want to split this technique. However, Comment LC-2860 resulted in deleting the second failure condition, so 2861 may need revisiting.
The objective of this technique is to ensure that Web pages can be interpreted consistently by user agents, including assistive technology. If specific relationships in a Web page are ambiguous, different user agents, including assistive technologies, could present different information to their users. Users of assistive technology, for example, may have different information presented to them than users of other mainstream user agents. Some elements and attributes in markup languages are required to have unique values, and if this requirement is not honored, the result can be irregular or not uniquely resolvable content.
An id attribute value that is not unique.
An SVG document uses id attributes on
title elements (for alternative text) in
order to reuse in other locations in the document. However,
one of the title elements has an id that is
also used elsewhere in the document, so the document is
ambiguous.
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Check that elements or attributes that refer to unique identifiers inside the same document have a corresponding id value.
Note that for XML document types defined by a DTD, this refers to attributes of type ID, IDREF or IDREFS. For XML document types defined by a W3C XML Schema, this refers to elements or attributes of type ID, IDREF or IDREFS. (For compatibility, the types ID, IDREF and IDREFS should only be used on attributes, but using them for elements is possible, according to XML Schema Part 2: Datatypes Second Edition.) For other schema languages, check the corresponding mechanisms for specifying IDs and references to IDs.
If #1 is false, then this failure condition applies and the content fails Success Criterion 4.1.1.