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Re: @headers on th too or just td?

From: Dan Connolly <connolly@w3.org>
Date: Thu, 26 Jun 2008 15:55:30 -0500
To: Robert J Burns <rob@robburns.com>
Cc: "public-html@w3.org WG" <public-html@w3.org>, public-comments-wcag20@w3.org
Message-Id: <1214513730.11021.385.camel@pav.lan>

On Thu, 2008-06-26 at 22:56 +0300, Robert J Burns wrote:
> HI Dan,
> 
> On Jun 26, 2008, at 9:49 PM, Dan Connolly wrote:
> 
> > I did a little investigation into ISSUE-20 table headers...
> >  http://www.w3.org/html/wg/tracker/issues/20
> > attached are a couple files I was trying to make
> > into test cases.
> >
> > The first one is from relevant WCAG 2 technique that somebody
> > referred me to...
> >
> > H43: Using id and headers attributes to associate data cells with  
> > header
> > cells in data tables from Techniques for WCAG 2.0
> > http://www.w3.org/TR/WCAG20-TECHS/H43.html
> >
> > I played around with that and validator.nu which led
> > me to discover that the current HTML 5 draft allows
> > @headers on td but not on th.
> >
> > "The td element may have a headers content attribute specified."
> >  -- http://www.w3.org/html/wg/html5/#the-td
> >  Editor's Draft 25 June 2008
> >
> > I suppose that suffices as far as I know... I can't
> > see any particular reason to use @headers on th, though
> > this does suggest the example in the WCAG 2 techniques
> > should get revised.
> 
> For authoring simplicity headers on TH cells is more important than  
> headers on TD cells. In fact it would be better for document  
> conformance to allow them only on TH cells than to allow them on TD  
> cells. A properly specified data / header cell association algorithm  
> will already associate data cells with the most immediate header  
> cells. Allowing authors to associate those header cells with other  
> header cells means that authors only add the IDREF to a few header  
> cell rather than maybe thousands of data cells.

just when I thought I was starting to understand this stuff...
now I'm totally confused.

In H43, how would a screen reader know that 15% goes with
both "Exams" and "1" without a headers attribute
on the <td>?

> I'm not aware if Ben came up within tables that needed headers on the  
> TD cells, but I can't come up with any off of the top of my head (as  
> long as @headers can be used on TH cells). However, not allowing  
> @headers on TD cells means authors have to repeat the same attribute  
> value thousands of times in some tables (where it would otherwise be  
> once or twice).
> 
> Take care
> Rob
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
gpg D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Thursday, 26 June 2008 20:54:07 GMT

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