HTML and XHTML documents that include images that cannot be described in a short text alternative.
This technique relates to Success Criterion 1.1.1: Non-text Content (Sufficient).
The objective of this technique is to provide information in a file designated by
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.
Authors can provide a description for an image by including text in a separate resource or within the text of the page containing the image. An advantage of using a separate resource for the description is that it is easily reusable for multiple instances of the same image, it does not add on-page visual clutter to the original document, and the description's end-point is apparent to the user. An advantage of providing the description within the same page as the image is that all users can access the description. A limitation of the on-page method, as well as in providing multiple descriptions on a single separate page, is that current implementations supporting longdesc do not identify the long description's end-point. Authors can solve this by providing a well-formed description, which identifies the where the description ends.
Example 1: Using longdesc to refer to a long description contained on a separate resource.
<p><img src="chart.gif" alt="a complex chart" longdesc="chartdesc.html"/></p>
Example 2: Using longdesc to refer to a long description within the same page.
<img longdesc="thispage.html#desc" alt="Line graph of the number of subscribers" src="http://www.company/images/graph.png"> <div id="desc"> <h3>Long Description: Line graph of the number of subscribers</h3> <!-- Full Description of Graph --> <p>Long description ends.</p> <div>
Resources are for information purposes only, no endorsement implied.
- Check that the
imgelement has a longdesc attribute.
- Check that the value of the
longdescattribute is a valid URI of an existing resource.
- Check that the content at the target of that URI contains a long description describing the original non-text content associated with it.
- #1 through #3 are all true