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From: Paul Bohman
Date: Jan 12, 2005 10:35AM

In light of the discussion about long descriptions and the longdesc
attribute, I thought I'd give a little input on the techniques of
providing descriptions for complex images, though I realize that my
response will address a larger concern than the specific issue brought
up (how to describe evacuation routes).

In general, there are 4 ways to describe complex graphics, listed below
in order of effectiveness (for most situations):
1. Provide the long description in the context of the document itself.
2. Provide a link to a long description via a normal text link.
3. Provide a link to a long description via the longdesc attribute.
4. Provide a link to a long description via a "d" link.

For the majority of cases, it is best to provide the text within the
same document as the image, because that way everyone can access it
without having to go to another page and without having to worry about
problems with assistive technologies or browsers.

The other options listed above may fit different circumstances, but are
less universal.

Both the longdesc attribute and the d-link concept were
well-intentioned, but problematic in terms of technology support, and in
terms of implementation--on a conceptual level--even within the best
technologies.

A bit more detail is available in the WebAIM tutorial at:
http://www.webaim.org/techniques/images/6

--
Paul Bohman
Director of Products and Services
WebAIM (Web Accessibility in Mind)
www.webaim.org
Utah State University
www.usu.edu