Techniques for WCAG 2.0

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# F17: Failure of Success Criterion 1.3.1 and 4.1.1 due to insufficient information in DOM to determine one-to-one relationships (e.g., between labels with same id) in HTML

## Applicability

Applies to the Document Object Model (DOM) for HTML and XHTML

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 it is 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. For example, when id attribute values are not unique, they are particularly problematic when referenced by labels, headers in data tables, or used as fragment identifiers, as user agents do not have enough information to provide determine essential relationships (i.e., to determine which label goes with which item).

## Examples

### Failure Example 1

- A label element whose for attribute value is an idref that points to a non-existent id

- An id attribute value that is not unique.

- An accesskey attribute value that is not unique

## Resources

No resources available for this technique.

## Related Techniques

(none currently listed)

## Tests

### Procedure

1. Check for id and accesskey values which are not unique within the document.

2. Check that attribute values that have an idref value have a corresponding id value.

3. For tables that use the axis attribute, check that all values listed in the axis attribute have a corresponding id value in a table header cell in the same table.

4. For client-side image maps, check that the value of the usemap attribute has a corresponding id value if the usemap attribute is not a URI.

### Expected Results

- If step #1, step #3 or step #4 is true or step #2 is false, then this failure condition applies and the content fails the success criterion.

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