W3C home > Mailing lists > Public > public-html-a11y@w3.org > April 2011

Re: [text] starter draft of clarification on alt validation, for discussion

From: Judy Brewer <jbrewer@w3.org>
Date: Mon, 25 Apr 2011 13:18:57 -0400
Message-Id: <E1QEPUD-0000Wz-2V@maggie.w3.org>
To: HTML Accessibility Task Force <public-html-a11y@w3.org>
Note that based on the discussion today
http://www.w3.org/2011/04/25-text-minutes.html
some of the items and the content in the response below will be changing.

Summary as of the end of today's "Text Alternatives Sub-Group" call 
include, with respect to the six sub-decisions on validation of alt:
- aria-labelledby -- leave as is (no response)
- role=presentation -- Rich & Steve discussing, will propose text to the list
- meta name=generator -- John drafting (with Leif? Judy invite)
- private communications -- leave as is (no response)
- title -- Steve and Geoff will each propose additional content
- figcaption -- Geoff & Judy discussing, will propose text to the list

We're looking for responses on these by mid-week, so that we can 
prepare a comprehensive clarification email by Friday that the Text 
Alternatives Sub-Group can review for potential consensus at our 
upcoming call on Monday May 2nd.

Thanks,

- Judy

At 11:55 AM 4/25/2011 -0400, Judy Brewer wrote:
>DRAFT for discussion purposes only.... partly for approach, party 
>for content...
>
>[DRAFT]
>
>Dear All,
>
>With regard to the HTML Working Group Co-Chairs' decisions, as 
>described in the following email...
>
>http://lists.w3.org/Archives/Public/public-html/2011Apr/0451.html
>
>
>...which discussed the following information...
>
>>There is a basic disagreement in the group on the validity
>>requirements for alt.  The result was two issues, six change
>>proposals, and a straw poll for objections:
>>
>>http://www.w3.org/html/wg/tracker/issues/31
>>http://www.w3.org/html/wg/tracker/issues/80
>>http://lists.w3.org/Archives/Public/public-html/2010Jul/0050.html
>>http://www.w3.org/html/wg/wiki/ChangeProposals/ImgElement20090126
>>http://www.w3.org/html/wg/wiki/ChangeProposals/ImgElement20100706
>>http://www.w3.org/html/wg/wiki/ChangeProposals/ImgElement20100707
>>http://www.w3.org/html/wg/wiki/ChangeProposals/ImgElement20100510
>>http://www.w3.org/html/wg/wiki/ChangeProposals/ImgElement20100504
>>http://www.w3.org/2002/09/wbs/40318/issue-31-80-validation-objection-poll/results
>
>
>...and which arrived at the following six conclusions...
>
>>Therefore, the HTML Working Group hereby decides that:
>>
>>    * The presence of aria-labelledby does not make missing alt conforming.
>>    * The presence of role=presentation does not make missing alt conforming.
>>    * The presence of <meta name=generator> makes missing alt conforming.
>>    * Use of private communications does not, in itself, make 
>> missing alt conforming.
>>    * The presence of title makes missing alt conforming.
>>    * The presence of figcaption makes missing alt conforming.
>
>
>...and which furthermore proposed addressing these through 
>implementation of a combination of the following two Change Proposals...
>
>>The two Change Proposals closest to these results are those identified
>>as Requirement Set 1 and Requirement Set 4:
>>
>>     http://lists.w3.org/Archives/Public/public-html/2010Jul/0050.html
>>     http://www.w3.org/html/wg/wiki/ChangeProposals/ImgElement20100707
>>
>>These Change Proposals agree with each other and with the WG decision
>>on aria-labeldby, role=presentation and figcaption.
>>
>>On the generator mechanism and the title attribute, Requirement Set 1
>>aligns with the WG decision:
>>
>>     http://lists.w3.org/Archives/Public/public-html/2010Jul/0050.html
>>
>>On the email exception, Requirement Set 4 aligns with the WG decision:
>>
>>     http://www.w3.org/html/wg/wiki/ChangeProposals/ImgElement20100707
>>
>>Thus, overall, the WG adopts the Requirement Set 1 proposal with
>>regards to aria-labelledby, role=presentation, <meta name=generator>,
>>title and figcaption; but Requirement Set 4 with regards to the email
>>exception.
>
>
>...we note that the following information was not considered. The 
>respondents on the surveys mentioned above had not anticipated that 
>this information would be unknown to the Co-Chairs, and so have 
>described this information in some detail within this mail, and 
>presented test samples to illustrate failures associated with the 
>proposed approaches. These clarifications follow.
>
>
>On the Co-Chair's decision on aria-labelledby:
>
>>    * The presence of aria-labelledby does not make missing alt conforming.
>
>The purpose of alt is to provide alternative text on images, and to 
>allow a user agent to render text in place of the images when images 
>are turned off.
>
>As an example, applications such as Yahoo! mail render alt text for 
>images when web page content is embedded in a mail message. This 
>allows applications and browsers to only fetch images if a user 
>really needs them, improving download performance; and providing a 
>label to explain to the sighted user what is missing.
>
>aria-labelledby is used to reference a label that is already visible 
>on the page, similar to an image caption. Authors put these captions 
>or labels in order to assist the sighted user in providing context 
>about the user.
>
>Both the label and the alt text serve the same purpose when images 
>are turned off; and both provide a label. It does not seem 
>appropriate  to force the author to provide two labels for the same 
>image, and to have two labels rendered when images are turned of. 
>Both will supply a label or "name" for the image in the accessibility API.
>
>Consequently, we request that the Co-Chairs consider allowing 
>aria-labelledby to be used to point to a label as a suitable 
>alternative to alt.
>
>
>On the Co-Chair's decision on role=presentation:
>
> > * The presence of role=presentation does not make missing alt conforming.
>
>Alt having a value of "" tells the user and assistive technology 
>that the image is presentational. Yet, with alt="" an assistive 
>technology (AT) must still filter out the image when it has no 
>intrinsic value other than to be decorative or be used as a spacer.
>
>Unlike alt="", role="presentation" has the added value of removing 
>the image from the accessibility API object tree, effectively 
>filtering out the image and improving assistive technology 
>performance. Furthermore, a role of presentation is to state the 
>intent of the author in a declarative fashion. For these reasons, 
>role="presentation" should be considered a suitable alternative to 
>requiring alt when it adds no meaningful information to an AT.
>
>As background, note that in most cases, browsers map browser content 
>to platform accessibility APIs, and an accessible object with a 
>standard API interface is created for each DOM object in a web page. 
>These objects are referenced and communicated with by an AT to 
>process accessibility information about visible objects in the web page.
>
>
>On the Co-Chair's decision on the presence of title making missing 
>alt conforming:
>
> > * The presence of title makes missing alt conforming.
>
>Title has a completely different function from alt in HTML.
>
>Title is used to generate a tooltip, and is invisible when images 
>are turned off. Alt does not generate a tooltip, and is visible when 
>images are turned off.
>
>If title is allowed as alternative text over alt it will break 
>applications such as Yahoo! mail; it will also break a commonly-used 
>feature, in less powerful mobile phones, where images are turned off 
>to improve performance.
>
>If title were to be used in place of alt then when images are turned 
>off in the browser, nothing meaningful will be shown in the browser.
>
>Furthermore, having title take precedence over alt will result in 
>tooltips being generated on decorative images and spacers, which 
>would do tremendous harm to the user experience.
>
>It should be noted that title is used as a last resort when other 
>measures cannot be employed to compute the label or "name" of an 
>object in the accessibility API mapping for browsers.
>
>Please note the following demonstrations of failures resulting from 
>the proposed approach:
>
>http://www.paciellogroup.com/blog/misc/HTML5/alt-tests/screenshots.html
>
>
>On the Co-Chair's decision on the presence of figcaption making 
>missing alt conforming:
>
>* The presence of figcaption makes missing alt conform
>
>[clarification pending]
>
>
>Please let us know if additional clarification is needed, and thank 
>you in advance for your re-consideration.
>
>Regards,
>
>....
Received on Monday, 25 April 2011 17:22:15 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Friday, 27 April 2012 04:42:36 GMT