- From: Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com>
- Date: Thu, 19 Apr 2012 23:52:15 +0100
- To: Laura Carlson <laura.lee.carlson@gmail.com>
- Cc: "Michael[tm] Smith" <mike@w3.org>, public-html-a11y@w3.org
On Thu, Apr 19, 2012 at 12:24 PM, Laura Carlson <laura.lee.carlson@gmail.com> wrote: > If you have specific verbiage that you would like to propose to be included > that would enable you to support the details section of the CP please do elaborate. I was pointing out one implication that's been repeated in a few different contexts that doesn't make sense to me based on my understanding of the APIs involved. With respect to the CP as a whole … Your CP suggests we change the W3C HTML snapshot to make @aria-describedby referencing @hidden a "may" not a "should not". Maybe that's a good idea, but I'm not sure what rationale your CP offers for that change. ARIA vaguely defines algorithms for the calculation of accessible names and descriptions, but it does clearly state that calculated accessible names and descriptions are exposed as plain text. @aria-describedby may contribute to accessible names and descriptions. Therefore it would be bad practice to use @aria-describedby to point to elements which, when reduced to plain text by these algorithms, do not produce a good accessible name or description. It makes sense for this to be reflected in an author conformance requirement. But whether the referent elements are @hidden makes no difference to how they are reduced to plain text. Therefore it does not make sense to add this to the definition of HTML @hidden as though @hidden were the problem with reduction of markup to plain text: "This technique [referencing @hidden content with @aria-describedby] should not be used for longer content that have structured text (e.g., headings, anchors, list markup, table markup, etc.), as rich text is stripped to string text, resulting in all semantic structure being lost." ARIA should define what an accessible description is and set an author conformance requirement that accessible names and descriptions calculated according to its algorithm must be appropriate, giving some examples and explanations of good and bad usage. As far as I can tell from ARIA's normative requirements, HTML5 is free to define @hidden so that its elements have an effective label of the empty string in ARIA's algorithms if we wanted to prevent @hidden content ever being exposed as accessible names and descriptions. I think Jonas's suggestion that authors will use @aria-describedby to point to @hidden content whatever our specs say is a plausible argument against doing so. Even so, HTML5 is also free to say authors must not use @aria-describedby to @hidden content, regardless of how such markup is processed when they do. For example, we might want to forbid providing text alternatives for images using this technique, on the basis text alternatives should also be available in text-mode clients, when images are disabled, when images fail to load due to network failures, etc. but it's not clear how text alternatives referenced in this way should be incorporated into the view tree for user agents implementing the standardized rendering. If ARIA included a technique for creating a description-for relationship between two nodes in the tree that did not imply the reduction of the description node to plain text then it would be appropriate to forbid that technique to point to @hidden content on the basis that it's not clear how descriptions under @hidden could be made visible for user navigation and interaction for example with a screen magnifier. But ARIA does not have such a technique (yet) so this objection to referencing @hidden is not especially important. (Yes, the ARIA implementation guide suggests mapping @aria-describedby to a description-for relationship - available in IAccessible2, ATK, and UI Automation - and allowing users to navigate to that content. But as ARIA proper also requires user agents to expose @aria-describedby in accessible name and description calculation, best practice continues to dictate that users author under the assumption @aria-describedby will be exposed to the user as plain text.) -- Benjamin Hawkes-Lewis
Received on Thursday, 19 April 2012 22:53:04 UTC