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Re: Adaptive Image Element Proposal

From: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>
Date: Thu, 6 Sep 2012 01:49:59 +0200
To: Kornel Lesiński <kornel@geekhood.net>
Cc: public-html@w3.org, whatwg <whatwg@whatwg.org>
Message-ID: <20120906014959201677.b0236edd@xn--mlform-iua.no>
Kornel Lesiński, Wed, 05 Sep 2012 22:29:22 +0100:
> On Tue, 04 Sep 2012 22:53:57 +0100, Leif Halvard Silli wrote:

> so if I understand this correctly, the <picture> element can be 
> defined to allow "Name From: contents", and then it will work fine as 
> role="img" and structured alternative content in the element.

I agree that it could work the way you say. But I don't know if it 
should considered to be 100% equal to role=img. E.g if <picture 
role=img> would be treated different from <picture>, then they would 
not be equal. (One would expect that an explicit role=img on <picture> 
should have the same effect as if you apply role=img on e.g. a <div>.)

Also, I doubt that one can expect the mark-up to be handled as mark-up. 
AT would probably only see it as "flattened" content. We are in the 
same "land" as we are with other hidden content ...
 
>> You mean, treat <img>’s @alt like the <caption> of <table>, for
>> instance? That is: Make it <img> a required part of the <picture>
>> construct, for instance? I do think that integrating <img> into
>> <picture> as a part of the picture compound element, sounds
>> interesting. And it could be possible, I guess.
> 
> Not exactly required. Simply read alternative content from element's 
> content. If you find <img> there, then read its alt. If you find 
> text, table or something else, then read that.

So you want <picture>'s alternative text to be "whatever it contains". 
I don't rule that out. But it is not compatible with the img role - for 
the reasons I have outlined before, but also due to what I say below.

>> One thing to think about is this: If we e.g. have a <table> which we
>> declare as presentational, then we also, per the ARIA rules, declare
>> the elements that are part of the <table> construct of that particular
>> table (<td>, <tr> etc) as presentational. So, if <img> was seen as part
>> of <picture>, then, to declare <picture> as presentational would also
>> affect the <img>.
> 
> Yes, I think it makes sense.
> 
> <picture role=presentation></picture> would be equivalent to <img 
> alt=""> (presentational image).
> 
> <picture --role=img--></picture> would be equivalent to <img> (missing alt).

That's OK. And correct. But you don't mention this:

    <picture role=presentation><img alt="Content."></picture>

According to "normal" ARIA rules, the above would be a presentational 
<picture> with a non-presentational <img> inside. Because, here we 
touch a slightly confusing aspect of ARIA 1.0. At least until one gets 
it: role=presentation does not mean that the content is hidden *except* 
if the element is one where the accessible content of the native 
element is provided via attributes - as is the case for <img>.

So, unless we say that <img> has a *special* role in <picture> - that 
it is an integrated part of <picture> (same as <td> in <table>), then 
it does not make sense that <picture role=presentation> should have any 
effect on anything *except* on the <picture> element itself. But not on 
its children.

Because, you see: For non-void elements, if you apply role=img to them, 
then you hide their content, while if you apply role=presentation, then 
you "open them up". Whereas for void elements, like <img> and (in 
theory at least) <area>, then it is role=presentation that closes them 
and the native role that opens them up.

We could say that no *textual* content (and also no <img> elements with 
other roles than  presentation) inside <picture> would make the 
<picture> presentational. That would be congruent with the rule that 
says that an <img> with empty alt is presentational.

But we cannot say that role=presentation - in any by it self - should 
have any effect. Because we can, as I see it, not demand that 
role=presentation and role=img should work in a different way when 
applied to <picture> compared to when applied to other elements.

So - knock on woods - we only have two options:

Model (1): 
    Define <picture><img></picture> as a compound element where
    the content by default is provided via the <img> element but
    where other textual content by default is ignored. An
   'accessible content model' like that reminds *strongly* about
    role=img. In fact, it is role=img, with some twists.

    EXAMPLE:

    <picture>
     <img alt="I am a key content picture image. And I, the
               alt attribute of the img element, defines the
               accessible label of the picture element." />
         But! Everything outside the img element, such as this
         text, is by default ignored by AT.
    </picture>

Model (2):
    Say that <picture> defaults to role=presentation. I have to
    say that, in my book, what you have describes reminds about
    that! Keep in mind, also, that as long as a <picture>
    *only* contains an <img alt=foo> element, then for most
    intents and purposes, an AT user would not perceive any
    difference between model (1) and model (2). 

Keep in mind, as well, that if we went for model (1), then it would 
only take that the author manually added <picture role=presentation> to 
get the model (2). The really confusing thing, for model (1) would be 
if the author manually added <picture ROLE=IMG>, because then the AT 
would probably not look for alternative text in the <img> anymore. 
However, this could be solved by making it a conformance criteria to 
*not* apply role=img to <picture>.
     
The model (1) could probably be extended with e.g. the <desc> element 
that Laura suggested. In other words: One could create "fields" that 
would be handled in predefined ways. Note that model (1) does not 
follow role=img in a strict sense - only in the sense that a <picture> 
should by default be conveyed to users as an image.

I would say that the <canvas> model borders on model (2).

> <picture --role=img-->alternative</picture> would be equivalent to 
> <img alt="alternative"> (alternative present).
-- 
leif halvard silli
Received on Wednesday, 5 September 2012 23:50:35 GMT

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