HTML and XHTML
This technique relates to Success Criterion 2.4.3: Focus Order (Failure).
This document describes a failure that occurs when the tab order does not follow logical relationships and sequences in the content.
Focusable elements like links and form elements have a tabindex attribute. The elements receive focus in ascending order of the value of the tabindex attribute. When the values of the tabindex attribute are assigned in a different order than the relationships and sequences in the content, the tab order no longer follows the relationships and sequences in the content.
One of the most common causes of this failure occurs when editing a page where tabindex has been used. It is easy for the tab order and the content order to fall out of correspondence when the content is edited but the tabindex attributes are not updated to reflect the changes to the content.
The following example incorrectly uses tabindex to specify an alternative tab order:
<ol> <li><a href="main.html" tabindex="1">Homepage</a></li> <li><a href="chapter1.html" tabindex="4">Chapter 1</a></li> <li><a href="chapter2.html" tabindex="3">Chapter 2</a></li> <li><a href="chapter3.html" tabindex="2">Chapter 3</a></li> </ol>
If this list is navigated by the tab key, the list is navigated in the order Homepage, chapter 3, chapter 2, chapter 1, which does not follow the sequence in the content.
The tab order has been set explicitly in a Web page by providing tabindex attributes for all fields. Later, the page is modified to add a new field in the middle of the page, but the author forgets to add a tabindex attribute to the new field. As a result, the new field is at the end of the tab order.
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- HTML 4.01 Tabbing navigation
- If tabindex is used, check that the tab order specified by the tabindex attributes follows relationships in the content.
- If check #1 is false, then this failure condition applies and content fails the Success Criterion.