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Re: feedback requested on WAI CG Consensus Resolutions on Text alternatives in HTML 5 document

From: Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com>
Date: Mon, 17 Aug 2009 10:40:36 +0100
Message-ID: <4A892594.1020605@googlemail.com>
To: Maciej Stachowiak <mjs@apple.com>
CC: Steven Faulkner <faulkner.steve@gmail.com>, Ian Hickson <ian@hixie.ch>, HTMLWG WG <public-html@w3.org>, W3C WAI-XTECH <wai-xtech@w3.org>
On 17/08/2009 10:05, Maciej Stachowiak wrote:
>> In situations like:
>>
>> <a href="#"><img src="delete.png" alt=""></a>
>>
>> It's useful to AT for the "img" to be exposed and to be able to access
>> "src" attributes for the purpose of providing a substitute for proper
>> alternative text.
>
> If that's so, then wouldn't it be better for authors to use alt=""
> instead of role="presentation", so that AT can decide whether it needs
> to expose the image anyway?

I don't think role="presentation" is appropriate in that case. It's not 
a presentational image.

> In particular, if your example was marked up
> like this:
>
> <a href="#"><img src="delete.png" role="presentation"></a>
>
> Then isn't it equally necessary and appropriate for AT to expose that
> image?

I think it's important that W3C specs do not produce a situation where 
"role='presentation'" is likely to be widely misused in that way.

I don't think authors should add "role='presentation'" in such cases 
(they should write "alt" text for the control), or that authoring tools 
should add "role='presentation'" if authors fail to write "alt" text for 
controls, or that checkers should suggest "role='presentation'" for 
images that are the only content for controls (they should suggest 
supplying "alt" text).

There may well be a case for assuming authors will get this wrong, and 
saying that UAs should ignore "role='presentation'" for the purpose of 
calculating control text, but that should be fixed at the ARIA spec 
layer, as it's not a problem specific to HTML.

>> http://www.w3.org/TR/WAI-USERAGENT/guidelines.html#tech-missing-alt
>>
>> More tendentiously, perhaps, in situations like:
>>
>> <p>As you can see from the chart below, sales increased in 2008:</p>
>> <img alt="" src="chart.png">
>>
>> Even if users can't consume the chart themselves, it's useful to users
>> to be able to download or hotlink that referenced chart in a
>> collaborative environment (e.g. a corporate wiki).
>>
>> By contrast:
>>
>> <img alt="" src="bullet.png">
>>
>> really is purely decorative; in a collaborative environment that seems
>> likely to be generated by authoring software.
>
> And likewise for these examples - it seems like AT should be left free
> to apply heuristics.

In the first case, I don't think "role='presentation'" should be added 
(it a data chart not a presentational image); in the second case I think 
it should (it's a bullet).

Assuming correct use of the marker (I know, big assumption), the 
advantage for AT is being able to /totally/ ignore the second (purely 
decorative) image, while still providing some sort of access to the 
first. Isn't that an improvement on heuristics?

Furniture photo for a news article about sidewalk disrepair:

<img alt="" src="walking-man.jpg" role="presentation">

Tangentially, I would prefer a way to demark decorative media that was 
native to HTML, and that was mapped to but did not rely on the ARIA 
layer, so that all UAs could make use of it. For example, "User 
Style"-type views in Firefox and Opera, the mobile layout view in Opera 
Mini and so on could omit images, videos, and audio marked as 
decorative. The current ARIA draft seems to block this sort of use:

http://www.w3.org/TR/wai-aria/#ua_noninterference (public)

http://www.w3.org/WAI/PF/aria/#ua_noninterference (editor's)

e.g. <img alt="" src="walking-man.jpg" presentational>

      <object data="walking-man.jpg" presentational>

      <video presentational>

      <audio presentational>

(Yes, this might involve specifying error handling at the HTML layer 
too. :( )

--
Benjamin Hawkes-Lewis
Received on Monday, 17 August 2009 09:41:18 GMT

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