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RE: ALT tag vs. LONGDESC

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From: Jukka Korpela
Date: Mar 8, 2002 1:23AM

Kevin Price wrote:

> The W3C guidelines don't make it clear to me when exactly to
> use an ALT tag only or when to use the LONGDESC tag.

("Attribute", not "tag".)

I guess the inexactness is intentional: It is a matter of judgement, where
different things need to be considered, and any fixed limits could be
misleading.

The Guidelines recommend:

"For complex content (e.g., a chart) where the "alt" text does not provide a
complete text equivalent, provide an additional description using, for
example, "longdesc" with IMG or FRAME, a link inside an OBJECT element, or a
description link."

So the question is whether the alt text provides all the information needed.
I wouldn't interpret "complete" in an absolutely literal sense; for example,
an image could be a photo that contains lots of details that are irrelevant
for the communicative purpose.

Note that the Guidelines recommend providing additional description, without
fixing any particular technique, such as LONGDESC, for it. Personally, I'd
say that normal textual links are preferable, since they are so much better
supported, and would make the availability of textual alternative apparent
to everyone. It can be useful as an alternative even if the user has no
problems with seeing the image; maybe he understands the image better after
reading the textual alternative.

I was surprised at seeing that there _is_ some support to LONGDESC, though
it's not very obvious: Netscape 6 has the feature that if I right-click on
an image, then select "Properties", I get a popup box that contains the word
"Description" followed by the LONGDESC URL as a link. I wonder how many
people know about this possibility.

> It seems like there should be a
> number of character limit for an ALT tag.

There's no fixed limit, but there are different reasons to avoid line breaks
when writing an ALT attribute value. In practice, if the ALT text would be
longer than what conveniently fits into one line, I'd consider using a link
to a separate textual alternative, perhaps using an ALT attribute value that
just mentions this. But it's sometimes a tough decision. Things often work
smoother to people using pages without images if I can use longish ALT texts
when needed.

--
Jukka Korpela
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