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Not versus, but plus (was: ALT tag vs. LONGDESC)

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From: John Foliot - bytown internet
Date: Mar 7, 2002 3:01PM

Kevin,

EVERY <img> requires the ALT attribute, some *May* also require the LONGDESC
attribute on top of the ALT attribute. If the image is conveying
information beyond what would be on the surface, then employ the LONGDESC
attribute which links to a text file with a fuller explanation.

For example, you have a web page with an image of a pie chart:

<img src="piechart.gif" height="300" width="300" alt="pie chart showing
browser usage statistics" longdesc="/longdesc/piechart.html">

For non-graphic browsers, the alt tag is describing "what" the image is,
however, should the user wish to "see" what the percentages are, they would
follow the LONGDESC link to "piechart.html" which would be a text version of
the browser usage stats (it could be a simple .txt file as well).

To my knowledge, currently only IBM's HomePage reader supports the LONGDESC
attribute, so you may also see the "d" link used. While not a W3C
recommendation (nor I believe Section 508), some advocacy groups propose it
as a stop-gap measure while waiting for the browsers/assistive software to
catch up:

<img src="piechart.gif" height="300" width="300" alt="pie chart showing
browser usage" longdesc="/longdesc/piechart.html"><a
href="/longdesc/piechart.html" title="text description of user stats">d</a>

Some feel that the d-link is "ugly", but you could set the colour of that
link as the same colour as your page background (when browsers universally
support the visibility attribute of CSS2 you could use that as well):

<a href="pichart.html" title="text description of user stats"
style="visibility: hidden; color: White; font-size: 1pt;">d</a>

<opinion>
While normally I would say that we should never set font sizes as absolutes,
I'm also a believer of exceptions to every rule, and this would be one of
them. It could be argued that this may remove the link from text only
browsers, but generally they rarely (if ever) support style sheets anyway,
and we all need to accept the fact that aesthetics DO play a role in our
work. The d link is not mandated anywhere, it's inclusion is simply one
more assistive coding device that web developers may apply, and speech
browsers/screen readers will still "hear" this link. It's a balance thing,
and IMHO I've added more than I've removed...
</opinion>

The bottom line however is the use of LONGDESC is a judgement call, which is
one of the reasons why an automated "compliancy tester" (i.e.: Bobby or
equiv) is never the final word... it's a great testing tool, but not the
only one you should use (I believe even Bobby's web site says something to
the equivalent)

HTH

JF






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