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ISSUE-30 (Longdesc) Change Proposal

From: Charles McCathieNevile <chaals@opera.com>
Date: Mon, 26 Oct 2009 18:53:15 +0100
To: "public-html@w3.org" <public-html@w3.org>
Message-ID: <op.u2e5a1spwxe0ny@widsith.local>

I would like to propose that the longdesc attribute from HTML 4 be  
retained in HTML 5 as an allowed attribute on images. This implies the  
following changes to the spec:

at http://dev.w3.org/html5/spec/text-level-semantics.html#the-img-element  
img would also become interactive content with longdesc present. The  
longdesc attribute would be listed as an attribute for the element.

The attribute is described already in HTML 4 [1] 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. The example, which references an image but  
appears to provide useless alt text should not be copied from HTML 4.

Other sections that may change:,, 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. should mention it as a way to make the association between an  
image and the relevant text explicit. 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. 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.

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.

This would require conformance checking to accept the attribute as valid,  
and would imply maintaining the existing requirement on Authoring Tools[2]  
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.

[1] http://www.w3.org/TR/REC-html40/struct/objects.html#adef-longdesc-IMG
[2] http://www.w3.org/TR/ATAG-10/ makes several relevant requiremnts



Charles McCathieNevile  Opera Software, Standards Group
     je parle français -- hablo español -- jeg lærer norsk
http://my.opera.com/chaals       Try Opera: http://www.opera.com
Received on Monday, 26 October 2009 17:54:03 UTC

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