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[Bug 10455] Mint a describedby attribute for the img element

From: <bugzilla@jessica.w3.org>
Date: Sat, 28 Aug 2010 22:12:02 +0000
To: public-html-a11y@w3.org
Message-Id: <E1OpTd4-0008I0-7Q@jessica.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=10455


Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |bhawkeslewis@googlemail.com




--- Comment #12 from Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com>  2010-08-28 22:12:00 ---
When *combined* with sister technologies like ARIA and HTML+RDFa, doesn't HTML5
already meet Requirements 1 and 6?

> 1. A programmatic mechanism to reference a specific a structured
> description, internal or external to the document.

We can reference descriptions internal to the document:

   <img src="foo.jpg" alt="{Short alternative}" aria-describedby="long">
   <p id="long">{Long description}</p>

We can transclude long descriptions:

   <img src="foo.jpg" alt="{Short alternative}" aria-describedby="long">
   <iframe id="#long" href="long-description.html" seamless></iframe>

We can indicate a link points to a long description for an image:

   <img src="foo.jpg" id="image" alt="{Short alternative}"
        resource="long-description.html">
   <p>
       <a xmlns:dc="http://purl.org/dc/elements/1.1/" about="#image"
          href="long-description.html"
          rel="http://purl.org/dc/elements/1.1/description">
           Long description
       </a>
   </p>

We can reference an external resource as the long description with invisible
metadata:

   <img id="image"
        src="foo.jpg" 
        xmlns:dc="http://purl.org/dc/elements/1.1/"
        alt="{Short alternative}"
        about="#image"
        rel="dc:description"
        resource="long-description.html">

> 6. A method to reference a longer description of an image, without including
> the content in the main flow of a page.

"aside" designates content that is not part of the "main flow". This could be
combined with "aria-describedby" like so:

    <img alt="Short alternative" aria-describedby="long">
    <aside id="#long">Long alternative</aside>

Requirements 2-5 look like UI requirements, rather than requiring additional
language features.

I may be mistaken, but I think ARIA, HTML5, and HTML-RDFa technologies allow
user agents to adopt the UI behaviour detailed in Requirements 2-5 in relation
to "dc:description", "aria-describedby" and "aside". (If someone believes they
do not, could they please cite where the drafts forbid which behaviour
described?)

I've no objection to including non-normative suggestions for UI in these
drafts, or other documents such as the ARIA User Agent Implementation Guide 1.0
or UAAG 2.0 Techniques. But, in general, ARIA, HTML5, and HTML-RDFa do not
*mandate* any particular UI, and I don't think that they should make an
exception for long descriptions. I've no particular reason to think user agents
*will* adopt the described behaviour, but I've little confidence in the magic
power of the spec to force them too either, or any reason to believe such ex
cathedra mandates would be ideal for all users in all circumstances.

I've elaborated how I think HTML5 could meet Requirements 1 and 6, and be have
conforming implementations meeting Requirements 2-5, when used together with
these other technologies.

However, I've argued elsewhere that HTML5 should maintain a *native* facility
for designating long alternatives for "img" elements, and that on balance
keeping "longdesc" is the best choice:

http://www.w3.org/2002/09/wbs/40318/issue-30-objection-poll/results

If we do mint a new feature and it differs significantly from
"aria-describedby" (for example, by taking a URI as a value rather than an
IDREF), then it should be called something *other* than "describedby" to reduce
confusion on the part of authors (e.g. a "longdescriptionhref" attribute or a
"longdescription" element).

But if we mint a new feature because "aria-describedby" is *not* sufficient for
image long descriptions - for example, if being able to reference external
documents as long descriptions is critical - then we should also be trying to
fix ARIA (the generic level).

Looking at the above, the key reason proposed for minting a new attribute
differing from "aria-describedby" is in order to designate external documents
as long descriptions. Why do users need this? Why hasn't PFWG expressed this
requirement in ARIA?

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Received on Saturday, 28 August 2010 22:12:03 UTC

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