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Meaningful Sequence
Guideline
When the sequence in which content is presented affects its meaning, a correct reading sequence can be programmatically determined.
Intent
The intent of this regulation is to enable a user agent to provide an alternative presentation of content while preserving the reading order needed to understand the meaning. It is important that it be possible to programmatically determine at least one sequence of the content that makes sense. Content that does not meet this Success Criterion may confuse or disorient users when assistive technology reads the content in the wrong order, or when alternate style sheets or other formatting changes are applied.
A sequence is meaningful if the order of content in the sequence cannot be changed without affecting its meaning. For example, if a page contains two independent articles, the relative order of the articles may not affect their meaning, as long as they are not interleaved. In such a situation, the articles themselves may have meaningful sequence, but the container that contains the articles may not have a meaningful sequence.
The semantics of some elements define whether or not their content is a meaningful sequence. For instance, in HTML, text is always a meaningful sequence. Tables and ordered lists are meaningful sequences, but unordered lists are not.
The order of content in a sequence is not always meaningful. For example, the relative order of the main section of a Web page and a navigation section does not affect their meaning. They could occur in either order in the programmatically determined reading sequence. As another example, a magazine article contains several callout sidebars. The order of the article and the sidebars does not affect their meaning. In these cases there are a number of different reading orders for a Web page that can satisfy the Success Criterion.
For clarity:
- Providing a particular linear order is only required where it affects meaning.
- There may be more than one order that is "correct" (according to the WCAG 2.0 definition).
- Only one correct order needs to be provided.
Finding Applicable Components
Look at the content on the original page to determine the logical order.
Inspecting and Using Components
- Turn off stylesheet for the selected page. It may be necessary to view the source or style editor tab in the browser developer tools to turn off individual stylesheets.
- Check to see if the order of content yields the same meaning as the original.
Section 508/WCAG 2.0 Failure Conditions
- When stylesheets are disabled, does the logical order of the content differ from the original page?
- Fails 1194.22(d): Readable Style Sheets.
- Fails 1.3.2 Meaningful Sequence.
Reporting Test Results
Any failure in Section 508 Failure Conditions results in: Fails Baseline Requirement #22.
When CSS is disabled, all meaningful images stay AND the logical order remains then: Passes Baseline Requirement #22.
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