ChangeProposals/longdesc

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Issue 30 longdesc Change Proposal

The following is the Change Proposal for ISSUE 30

Editor: Charles McCathieNevile (chaals@opera.com)

Please address feedback to the HTML Working Group mailing list (public-html@w3.org).

Summary

I would like to propose that the longdesc attribute from HTML 4 be retained in HTML 5 as an allowed attribute on images.

Details

This implies the following changes to the spec:

at img would also become interactive content with longdesc present. i.e. add "or longdesc" after "usemap" in the phrase "If the element has a usemap attribute" under the 'Categories' item. The longdesc attribute would be listed as an attribute for the element. i.e. Add "longdesc" to the list of content attributes, and "attribute DOMString longdesc;" to the attributes listed in the DOM Interface for the img element.

The longdesc attribute is described already in HTML 4 and the description can be re-used, although it should be made clear that the URI to which longdesc refers can be a relative reference to some part of the same page (in order to be explicit about which content is associated with the image), or a different page. I.e. in the first sentence at [1], add text such as "which may refer to a point within the current page or to a different page" after the work "link".

The example, which references an image but appears to provide useless alt text should not be copied from HTML 4.

Other sections that should change:

  • 4.8.2.1.1, 4.8.2.1.2, 4.8.2.1.3 should all mention that a longdesc *may* be provided to provide a detailed *description* of the image, e.g. to help a person who cannot see it to find it from a description.
  • 4.8.2.1.5 should mention it as a way to make the association between an image and the relevant text explicit.
  • 4.8.2.1.6 should mention it as the preferred way to point to a description of the image if this is desired, rather than mis-using the alt attribute for this purpose.
  • 4.8.2.1.9 should mention that where an image is a key part of the content, it should have sufficient text in the alt attribute to replace the image, and using the longdesc attribute for critical information is a mistake. However, it can be used for additional information if desired.

Rationale

This has been a controversial topic. It is clear that longdesc is relevant only to a fraction of images on the Web, and that it is only provided in a few of the cases where it is actually relevant. It is also clearly subject to bogus values to a large extent (perhaps the majority of the time). And its use is relatively limited, even by those who might be expected to appreciate it.

However, it has been implemented multiple times successfully. The fact that there is bad data associated might account for low overall usage, but has relatively little impact on implementations, which can readily choose to simply ignore values which are not URIs, or even to present the value to the user, and relatively little impact on the user, who can still benefit from a *good* usage.

Impact

This has no impact on existing HTML-4 browsers, many of which fail to make longdesc accessible other than via the DOM. Failure to make this change will have an impact on assistive technologies such as screen readers, which use the longdesc attribute to find descriptions of images.

This would require conformance checking to accept the attribute as valid, and would imply maintaining the existing requirement on Authoring Tools to allow the author to use this functionality. It would maintain conformance of HTML-4 tools and content, rather than the current expected change leaving them non-conforming.

References

  1. longdesc in HTML 4.01
  2. The Authoring Tool Accessibility Guidelines 1.0 makes several relevant requirements