Techniques for WCAG 2.0

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H45: Using longdesc


HTML and XHTML documents that include images that cannot be described in a short text alternative.

This technique relates to:

User Agent and Assistive Technology Support Notes

Some older assistive technologies do not support the longdesc attribute.


The objective of this technique is to provide information in a file designated by the longdesc attribute when a short text alternative does not adequately convey the function or information provided in the image. The longdesc attribute is a URI, the target of which contains a long description of the non-text content.


Example 1

Example Code:

<p><img src="chart.gif" alt="a complex chart" longdesc="chartdesc.html"/></p>


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  1. Check that the img element has a longdesc attribute.

  2. Check that the value of the longdesc attribute is a valid URI of an existing resource.

  3. Check that the content at the target of that URI contains a long description describing the original non-text content associated with it.

Expected Results