Understanding Success Criterion 1.3.2: Meaningful Sequence

Success Criterion 1.3.2 Meaningful Sequence (Level A): When the sequence in which content is presented affects its meaning, a correct reading sequence can be programmatically determined.

Intent

The intent of this Success Criterion 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:

  1. Providing a particular linear order is only required where it affects meaning.
  2. There may be more than one order that is "correct" (according to the WCAG 2.0 definition).
  3. Only one correct order needs to be provided.

Benefits

Examples

Related Resources

Resources are for information purposes only, no endorsement implied.

Techniques

Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this Success Criterion. However, it is not necessary to use these particular techniques. For information on using other techniques, see Understanding Techniques for WCAG Success Criteria, particularly the "Other Techniques" section.

Sufficient Techniques

  1. Ordering the content in a meaningful sequence for all the content in the Web page
  2. Marking sequences in the content as meaningful using one of the following techniques AND Ordering the content in a meaningful sequence for those sequences

  3. Making the DOM order match the visual order
  4. Using the tabIndex property to specify a logical reading order in Flash
  5. PDF3
  6. SL34

Advisory Techniques

Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.

Failures

The following are common mistakes that are considered failures of this Success Criterion by the WCAG Working Group.

Key Terms

correct reading sequence

any sequence where words and paragraphs are presented in an order that does not change the meaning of the content

programmatically determined

determined by software from author-supplied data provided in a way that different user agents, including assistive technologies, can extract and present this information to users in different modalities

Determined in a markup language from elements and attributes that are accessed directly by commonly available assistive technology.

Determined from technology-specific data structures in a non-markup language and exposed to assistive technology via an accessibility API that is supported by commonly available assistive technology.