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

From: Leif Halvard Silli <lhs@malform.no>
Date: Tue, 23 Sep 2008 11:31:37 +0200
Message-ID: <48D8B779.6050508@malform.no>
To: James Craig <jcraig@apple.com>
CC: Al Gilman <alfred.s.gilman@ieee.org>, Chris Wilson <Chris.Wilson@microsoft.com>, W3C WAI-XTECH <wai-xtech@w3.org>, public-html@w3.org, Gez Lemon <gez.lemon@gmail.com>

James Craig 2008-09-23 04.32:

> 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.


> [snip] 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. 


What 99%? Those when authors have not used any TH cells at all?

HTML 4 already has a such clearly-defined algorithm for finding 
heading information, when TH cells *are* present, see section 
11.4.3. (And even better: that algorithm incoroprates @headers.)

Just as a @scope-like algorithm can be generalised to work also 
when there is no @scope and not even any TH cells, the general 
@headers-incoprating algorithm of HTML, can also be extended to 
work under the same circumstances.

> 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?

Have you are anyone calculated how far we would come if we dropped 
@scope and instead went 100% for @headers?

Note: the @headers-incorporating algorithm of HTML 4, is part of 
the @headers feature there. You must take that into account when 
counting how often you see the @headers attribute.

> 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. [snip]


What you say here would still apply even if we go for @headers 
instead of @scope: It is more vital - covers more broadly - if one 
first uses TH cells properly before considering @headers.

The HTML 5 draft's point of view, is that @scope is natural, and 
@headers is extra. That view is false. We have 3 choices: @scope, 
@headers or both.

Currently the draft proposes to use both, allthough @headers is 
reduced to the very stupid use of it that you argues against. 
(Just as it is stupid to use @scope if the algorithm makes it 
unneccessary, it is also stupid to use @headers if the 
@headers-like algorithm of HTMl 4 makes it unneccessary.) [That 
said, when using @headers, we are at least doing something that AT 
can take advantage of.]

If we really want to simplify, we could just as well drop @scope 
entirely, and only go for @headers. That would allow us to have 
one attribute less.

Al said:
 >> + note: @scope-like markup requires more burdensome processing 
 >> on the client side to get the associations to the user than
 >> does @headers-like markup.

I would assume that Al does not consider the general algorithm of 
HTML 4 as "@scope-like". @scope and "@scope-like" solutions start 
with the header cells and "propagate" the headerness to the other 
cells. The @headers-incorporating algorithm of HTML 4, as well as 
the very @headers attribute, starts with the cell and looks for 
the header cells. So it should be simpler.


>> ++ 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.

Here I agree with you. This is also the way HTML 4 sees it.
-- 
leif halvard silli
Received on Tuesday, 23 September 2008 09:32:24 UTC

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