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

hi benjamin,
>I'm hoping "role='presentation'" will be used more specifically than how
alt="" has been used in practice, such >that UAs could distinguish between,

as i said previously, i do not consider providing a disitnction between
alt="" and role="presentation" to be useful. it will provide more complexity
for the author, with no gain as far as i can see.


>Example use-case: Joe is a blind advanced screen reader user putting
together a presentation about his >company's performance over the past year.
He goes to the corporate wiki and finds references to charts for >sales in
2008 and profit/loss margins in 2008, but can't find them when reading
through the page. He switches >to a mode that exposes even images with
alt="" and retrieves the charts based on the document sequence.

your example is clearly one that will happen seldomly so arguments about the
relative performance aspects of using the dom over msaa is moot, besides as
I said AT already use the DOM to gain access to a range of other elements.
Providing a mode that makes all img elements  in a document satisfies the
use case you have provided.

>Requiring UAs not to push such images into MSAA seems like a significant
change, so it's worth making sure >it /definitely/ helps AT rather than
hinders them.

doesn't seem that signifcant to me, the purpose of using alt="" is to hide
images from AT, as is  role="presentation" having a common mechanism would
be progess, anyway I will talk to david bolter and marco zehe the
accessibility guys from mozilla to see what they think about it.

>The best way to answer that question may be to ask AT developers which
subset of images they would prefer >included in the accessibility tree. Has
anyone already performed and (ideally) documented that research to a >level
of detail where it could answer the question for my example markup?

not that i know of, please go ahead, if you think it would be worthwhile.
What can be said is that ARIA has been implemented in browsers and AT in
close consultation with the AT vendors, they have not to my knowledge raised
in issues in relation to restricting the scope of role="presentation"
because of concerns regarding its use.

>1. Only the former works with legacy UAs.
>2. Only the former would be usable by current and future UAs (text
browsers, GUI browsers with images >disabled, GUI browsers applying user
styles, any browser when the image download fails, etc.).

in regards to point 1 - practically the lack of an alt attribute and the use
of alt="" have very little practical difference to how AT treat these <img>
elments
in regards to 2 why would only the former be usable by current and future
UA's?
I can style a role="presentation" image

img[role="presentation"] {border:2px solid red}

what practical difference will there be for a gui browser with an alt="" or
role="presentation"?
or a text browser? or any browser when the image download fails?

regards
stevef


2009/8/17 Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com>

> On 17/08/2009 16:39, Steven Faulkner wrote:
>
>> the AT could just as well support a mode where all images are
>> available including those with role="presentation"
>>
>
> It certainly could support a mode that even exposed images with
> "role='presentation'".
>
> It doesn't follow that would be "just as well" (e.g. for meeting Joe's use
> case) as a mode that excluded those images.
>
> I'm hoping "role='presentation'" will be used more specifically than how
> alt="" has been used in practice, such that UAs could distinguish between:
>
>   * images with non-empty text alternatives (e.g. "alt='Sales chart'")
>   * images with empty text alternatives (which can mean a variety of things
> in the web corpus even if it has only one conforming use in HTML5)
>   * images entirely missing text alternatives
>   * images that are definitely decorative (e.g. "role='presentation'" or,
> preferably, "presentational")
>
> Exactly what combination of images a UA chooses to expose in any given mode
> is very much up to the UA.
>
> Currently, the nightly build of Firefox pushes
>
>  <img alt="" src="sales.png">
>
> into MSAA with role equals graphic and name equals null.
>
> Requiring UAs not to push such images into MSAA seems like a significant
> change, so it's worth making sure it /definitely/ helps AT rather than
> hinders them.
>
> You'd also need to make sure that images like:
>
>  <img alt="" title="Sales" src="sales.png">
>
> (or similar sources of text alternatives) were still pushed into MSAA.
>
> > this could be achieved by accessing the HTML DOM rather than the
> accessibility API's
>
> When access to the raw DOM is provided to AT (which is not required for
> conformance with WAI-ARIA as far as I can tell - perhaps it should be!), it
> certainly could be achieved that way.
>
> But when deciding whether to instruct UAs to treat "<img alt='' ...>" the
> same as "<img alt='' role='presentation'>", the question is does it help or
> hinder AT developers to exclude "<img alt='' ...>" from exposure in the
> accessibility tree?
>
> I've not done any serious AT programming myself, but I had a discussion
> with a commercial screenreader developer a couple years ago and they said
> that extracting information from the IE's DOM API was less efficient than
> extracting information from IE's MSAA API.
>
> Based on that, I think whether these "img" elements should be in the tree
> or out of it depends on how often AT wants to expose their presence to end
> users, compared to other "img" elements with and without
> "role='presentation'". The best way to answer that question may be to ask AT
> developers which subset of images they would prefer included in the
> accessibility tree. Has anyone already performed and (ideally) documented
> that research to a level of detail where it could answer the question for my
> example markup?
>
> Regardless of the answer to that question, I think it would be actively
> harmful for HTML5 checkers to suggest replacing "alt=''" with
> "role='presentation'", even for images that are not a source of repair text
> for controls, since:
>
> 1. Only the former works with legacy UAs.
> 2. Only the former would be usable by current and future UAs (text
> browsers, GUI browsers with images disabled, GUI browsers applying user
> styles, any browser when the image download fails, etc.).
>
> I think HTML5 checkers should only give advice about when to add
> "role='presentation'" to "alt=''" if that can cause the image to be treated
> differently by ATs, since:
>
> 1. I don't think teaching authors about language features is a good reason
> to hassle them to add them redundantly.
> 2. Otherwise, I'm unaware of another use case for "role='presentation'" in
> conforming HTML5. Is there one? If there is a use case elsewhere, then
> that's where the advice should be triggered, not on "img".
>
> Likewise, if HTML5 were to add a "presentational" attribute, I don't think
> authors should be advised to replace "alt" with it, and I don't think it
> should be included at all unless it can cause the image to be treated
> differently by UAs.
>
> --
> Benjamin Hawkes-Lewis
>



-- 
with regards

Steve Faulkner
Technical Director - TPG Europe
Director - Web Accessibility Tools Consortium

www.paciellogroup.com | www.wat-c.org
Web Accessibility Toolbar -
http://www.paciellogroup.com/resources/wat-ie-about.html