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Technique H45:Using longdesc

Obsolete

The longdesc attribute is obsolete in the HTML Living Standard, and was never widely supported. Use an a element or an image map to link to the description.

About this Technique

This technique is not referenced from any Understanding document.

This technique applies to HTML documents that include images that cannot be described in a short text alternative.

Techniques are examples of ways to meet Web Content Accessibility Guidelines (WCAG). They are not required to meet WCAG. Content can satisfy the normative requirements of WCAG even if it does not use any of the documented techniques. See About WCAG Techniques.

Description

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.

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.

Examples

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>

Related Resources

No endorsement implied.

Tests

Procedure

  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

  • #1 through #3 are all true
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