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Re: function and impacts (was: @scope and @headers reform)

From: James Craig <jcraig@apple.com>
Date: Mon, 22 Sep 2008 19:32:09 -0700
Message-Id: <FE82D4E2-2DB3-49EF-93A6-66EC0C390980@apple.com>
To: Al Gilman <alfred.s.gilman@ieee.org>, Chris Wilson <Chris.Wilson@microsoft.com>
Cc: W3C WAI-XTECH <wai-xtech@w3.org>, public-html@w3.org, Gez Lemon <gez.lemon@gmail.com>

Al Gilman wrote:

> + note: I think we should be able to come up with a definition
> of header hierarchy where there is consensus that this is present
> in the table genre that we have to cover.  It's widespread.

In most regular table/grid cases, it may be a more productive effort  
to define the implicit scope for headers that do not have an explicit  
author-defined association with cells. For example, "headers inside  
first row or table header group assume col scope, and first-cell  
headers in the table body group assume row scope" with some caveats  
for conflicts. In over 99% of the cases, a clearly-defined algorithm  
for calculating implicit scope is going to replace the need for  
explicit author-defined associations. In most of the other edge cases  
@scope will suffice, and in very rare cases, a more explicit  
association could be achieved via @headers or @aria-labelledby.

It is my understanding that @headers, while valuable, is almost never  
used. Like the long-term longdesc testing, has there been any attempt  
to determine where and how often @headers is used?

In most cases where @headers is necessary, the author would do better  
to change the information architecture of the table into a more  
understandable form, instead of "accessifying" an already overly  
complex table grid. Although the section does not explicitly mention  
tables, this is in line with the WCAG 1.0 recommendation to convey  
information as simply as possible. In other words, if an HTML table is  
too complex for @scope, it's probably also too complex for non- 
disabled viewers to decipher it easily, even without assistive  
technology.

WCAG 1.0 Guideline 14. Ensure that documents are clear and simple.
http://www.w3.org/TR/WCAG10/#gl-facilitate-comprehension

> ++ browser provides via DOM a method to learn the "immediate critical
> context" (in bottom-up @headers-like direction) for cells that  
> combines
> the results of @scope-implications analysis with @headers data.  These
> are cumulative; @headers does not cancel @scope.

Assuming @headers sticks around and isn't replaced by something more  
general like @aria-labelledby, I don't agree with this scenario.  
Headers associated through scope (implicit or explicit) should be  
cumulative, but if an author has explicitly defined @headers, that  
specific association should cancel @scope.
Received on Tuesday, 23 September 2008 02:32:53 GMT

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