W3C home > Mailing lists > Public > public-html-a11y@w3.org > March 2012

Re: Drop longdesc, get aria-describedat?

From: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>
Date: Tue, 13 Mar 2012 17:44:26 +0100
To: Charles McCathieNevile <chaals@opera.com>
Cc: Silvia Pfeiffer <silviapfeiffer1@gmail.com>, John Foliot <john@foliot.ca>, RichardSchwerdtfeger <schwer@us.ibm.com>, W3C WAI-XTECH <wai-xtech@w3.org>, HTMLAccessibility Task Force <public-html-a11y@w3.org>
Message-ID: <20120313174426383822.80f525cd@xn--mlform-iua.no>
Charles McCathieNevile, Tue, 13 Mar 2012 08:08:46 +0100:
> On Tue, 13 Mar 2012 06:40:48 +0100, Leif Halvard Silli:
>> One thing that struck me, as I was writing this - at least the things
>> relating to fallback, is that much of what I was describing probably
>> only makes sense for the <img> element. Simply because only the <img>
>> element has a such a specific behavior whenever it isn't displayed.
> Longdesc isn't default fallback, it is extended support. (Or some 
> such terminology).

In the bug, then it was Alexey from Webkit who asked if the longdesc 
URL - that is to say: the link, not the content at the end of the link 
- should be rendered visually as a link 'if image loading is disabled'. 
I thought that sounded like a great idea, and hence I said 'yes' to 
that. Why would that be a bad idea?

Note that he had 'disabled image loading' - and not 'rotten image URL' 
- in mind, in case that is important. [There are less concerns when 
image are disabled, one should think.]

PS: The CSS WG has shown interest for being able to style broken 
images: http://lists.w3.org/Archives/Public/www-style/2012Jan/0168

PPS: In Opera, if @src points to something that Opera doesn't recognize 
as an image file, then the contextual menu fails to render, and so the 
long description becomes unavailable. Seems like a bug?

>> E.g. for <video>, <audio> etc, then there is no guaranteed fallback.
>> And even if there is fallback, it isn't guaranteed to be a textual
>> substitute.
> There's no guarantee that the long explanation of an image is 
> textual, either. (Somewhere there is an example I made with audio, to 
> illustrate a different idea, or think of multi-modal CAPTCHA).

Right. But that's completely another issue, AFAICT.

What I had in mind was, that when an image URL is broken, then we know 
what we get: We get the alt text, and in most browsers we also get an 
icon to signal 'lacking image'. For video, if the video URLs are broken 
or the forma is not supported, then -a- we do not get a 'lacking video' 
icon'; -b- we might get flash fallback; -c- we might get a link to 
download the file to the disk. In short: We don't know what we get. And 
so, we cannot, as easily, e.g. decide to render the longdesc URL as a 
link if the video doesn't render, because it might break the fallback.

>> This, IMO, points towards 'the HTML feature' rather than
>> 'an ARIA feature'.
> Right.

But note that the chairs have asked for *more* justification for why 
the CP ask for why @longdesc is needed specifically for <img>.
Leif Halvard Silli
Received on Tuesday, 13 March 2012 16:45:07 UTC

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