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Re: ISSUE-30 (Longdesc) Change Proposal

From: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>
Date: Thu, 29 Oct 2009 22:18:46 +0100
Message-ID: <4AEA06B6.7010006@xn--mlform-iua.no>
To: Charles McCathieNevile <chaals@opera.com>
CC: Jonas Sicking <jonas@sicking.cc>, "public-html@w3.org" <public-html@w3.org>
Charles McCathieNevile On 09-10-29 10.29:

> On Thu, 29 Oct 2009 07:29:52 +0100, Jonas Sicking:
>> On Wed, Oct 28, 2009 at 6:19 PM, Leif Halvard Silli:
>>> Jonas Sicking On 09-10-29 00.57:
>>>> On Wed, Oct 28, 2009 at 7:59 AM, Leif Halvard Silli:
>>>>> Jonas Sicking On 09-10-27 20.15:
>>>>>> On Tue, Oct 27, 2009 at 7:09 AM, Leif Halvard Silli:
>>>>>>>> I agree that @longdesc and @aria-describedby aren't exactly the  
>>>>>>>> same. However they are very similar.
> 
> Yes, they are.


[...]

>> The same can not be said for @longdesc ... Yes, there is
>> more than zero uptake, but I don't think there is enough to warrant
>> having duplicate (or near-duplicate) features.
> 
> There is significant uptake in the ancillary materials - the books,  
> courses, how-to pages and so on, that already use longdesc. Stripping it  
> out doesn't always make us friends either.
> 
> Since it isn't that complicated (Opera recently implemented it, in trivial  
> time, iCab has had it for ages as have screen readers that look for it on  
> their own, there is a nice plugin for Mozilla) and since it has a lot of  
> supporting material already, we can take advantage of that fact to explain  
> more of aria to authors.


And at least the IE+JAWS combo supports it as well.

> It is possible that we should deprecate longdesc  
> - point out that it is obsolete, *if* aria-describedby can do the same job  
> in the real world. But I don't think that day has yet arrived, and until  
> it does, leaving an existing and well-described HTML feature that is  
> useful (admittedly not to the whole universe, but to some people in some  
> cases) in the spec seems a more rational choice.

So, I am putting more weight on the differences than either of 
you, I guess. ;-)

One important reason I emphasize that @longdesc is different from 
aria-describedby is because it is a very simple technology - a 
link. A link to only just one resource. "Real" fallback is also 
always just one thing, and it is simple. Unlike aria-describedby, 
which can be used to collect several related resources into a 
whole. It is as if one may "mash up" a fallback text with it.

ARIA requires much more of the UA. And since I have never tried 
ARIA, I have a hard time imagining how it works. I also do not 
know how well it is supported. (And we're told that A11Y users 
upgrade less often.)

I also imagine that it is easy to do things wrong with it. Much 
has been said about the problem of hidden data etc. And such links 
that only A11Y users experience could easily become out of sync 
with the document.

  OK, the longdesc link is also kind of hidden for those who do 
not use A11Y equipment. But the longdesc thing is so tightly 
linked to the fallback idea, that it is is easy to understand, as 
author: All images should have fallback. Some of them in the form 
of a longdesc. And that' it.

I read about the "computation of a text equivalent" in ARIA ... 
But how can I be certain that I "compose" the fallback right? How 
can I be certain about how it will be presented at all?

I made a demo during my stay in this group, where I used CSS 
:target{} to hide and show the longdesc. Again, since it is a 
link, I know how to deal with a link.

But, of course, when aria-describedby only contains a single 
IDREF, then one may - as author - treat it more in the same way as 
one may treat @longdesc. And - in fact - then one could probably 
link to the very same description - simultaneously - with both 
@longdesc and aria-describedby - provided the description is kept 
inside the same document.

So, I see that the issues are related ... Heck, @alt is even 
included in the ARIA text equivalent computation algorithm. 
(While @longdesc doesn't seem to be ... Which seems odd to me. If 
the longdesc is part of the document then it could be included.)
-- 
leif halvard silli
Received on Thursday, 29 October 2009 21:19:27 GMT

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