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Re: conflation of issues or convergence of interests?

From: Jason White <jasonw@ariel.its.unimelb.edu.au>
Date: Sun, 29 Jul 2007 13:15:02 +1000
To: "Patrick H. Lauke" <redux@splintered.co.uk>
Cc: Lachlan Hunt <lachlan.hunt@lachy.id.au>, Sander Tekelenburg <st@isoc.nl>, public-html@w3.org, wai-xtech@w3.org
Message-ID: <20070729031502.GA4869@jdc.local>

On Sun, Jul 29, 2007 at 03:22:22AM +0100, Patrick H. Lauke wrote:

> But, unless I'm mistaken, no current UA even renders HTML5's <audio> and 
> <video>, so comparing how they currently handle HTML4's <object> may not be 
> all that relevant. And if the spec stated that UAs need to handle fallback 
> content a certain way (possibly making reference to UAAG 1.0 in passing as 
> well) that gives users control, would that be a likely step in the right 
> direction? 

Yes, that's moving in exactly the right direction.
> Or is the historically flaky implementation of <object> going to 
> kill this idea off right from the get-go?

It shouldn't kill the idea off at all. If there are concrete 
problems with OBJECT that can be avoided in the design of the new elements,
while still exposing the desired semantics, then those considerations should
be taken into account so as to facilitate implementation of <audio> and
<video>.

As mentioned earlier in this thread, a uniform means of referring to
alternative content is desirable for consistency reasons.

Implementors of HTML 4 are faced with ALT, LONGDESC and OBJECT, each having
its own semantics. Regrettably, ALT is likely to remain for some time to come,
due primarily to the inadequate content model of IMG. So, if ALT is left in
place, I would suggest simplifying the design by choosing a single mechanism
for (1) linking to alternative content, and (2) allowing block-level
alternative content to appear in a document. In both cases, the relationship
between the alternative content, and the primary content, would be explicit in
the markup.

The second requirement - block-level alternatives in the document itself,
could be dispensed with, as long as the UA is allowed to traverse the link to
the alternative content without user intervention, and to insert it into the
document. If the link is at the inline level, though, having block-level
content inserted into the document tree could pose significant problems, and
so far as I know, there are no existing conventions for dealing with document
fragments. Thus the best solution would appear to be
a block-level element:
<alt for="IDREF"> [alternative content belongs here - either a link or a full
alternative] </alt>

Open questions are:

1. Whether to allow multiple alternatives to refer to the same element, and if
so the semantics of the selection mechanism.

2. Whether to allow nested alternatives, as in OBJECT, which would achieve the
same result.

In comparing these and other options, including alternative proposals for
solving the same problem, the experience of implementors with OBJECT becomes
relevant and useful. For example, a "one alternative per resource" rule could
simplify implementation at the expense of flexibility, but on balance it might
be worth the trade-off - that's a matter which would need to be discussed.

If a general alternative content mechanism is introduced, I, for one, would be
comfortable to see LONGDESC relegated to history.
Received on Sunday, 29 July 2007 03:15:13 GMT

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