Techniques for WCAG 2.0

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# F62: Failure of Success Criterion 1.3.1 and 4.1.1 due to insufficient information in DOM to determine specific relationships in XML

## Applicability

Applies to the Document Object Model (DOM) for XML.

This failure relates to:

- Success Criterion 1.3.1 (Info and Relationships)
  - How to Meet 1.3.1 (Info and Relationships)
  - Understanding Success Criterion 1.3.1 (Info and Relationships)
- Success Criterion 4.1.1 (Parsing)
  - How to Meet 4.1.1 (Parsing)
  - Understanding Success Criterion 4.1.1 (Parsing)

## Description

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.

## Examples

### Failure Example 1

- 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.

- A DAISY document uses the `imgref` attribute on the `caption` element to link captions with images. However, `imgref` attribute value does not refer to the `id` attribute of the `img` element to which it belongs, so the user agent cannot find the caption for that image.

## Resources

Resources are for information purposes only, no endorsement implied.

## Related Techniques

(none currently listed)

## Tests

### Procedure

1. Check that all id values within the document (as defined by the schema) are unique.

2. 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.

### Expected Results

- If #1 or #2 is false, then this failure condition applies and the content fails the Success Criterion.

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