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Re: PFWG report on @headers status

From: Robert J Burns <rob@robburns.com>
Date: Tue, 25 Nov 2008 09:31:28 -0600
Cc: joshue.oconnor@cfit.ie, "Al Gilman" <Alfred.S.Gilman@ieee.org>, "Janina Sajka" <janina@a11y.org>, "Michael Cooper" <cooper@w3.org>, "Gez Lemon" <gez.lemon@gmail.com>, "HTML WG" <public-html@w3.org>
Message-Id: <0031B9C3-C46C-44E0-B2A2-DD33CFF860EF@robburns.com>
To: "Laura Carlson" <laura.lee.carlson@gmail.com>

Hi Laura,

On Nov 25, 2008, at 9:04 AM, Laura Carlson wrote:
> One thing that I would like to document in the Wiki is the design  
> notes sub-point on cyclic referencing. You mentioned:
>> There has bee some concern voiced about the potential for cyclic
>> references if chained headers were allowed in the specification. This
>> seems to some degree to be unfounded. The relationship between a
>> header and any corresponding chained/nested/ conceptual header that
>> follows it is uni-directional and not bi-directional. This also
>> follows if the id of a <td> cell is to be referenced from a chained
>> header.
> How is this point semi-founded? How can it be addressed and resolved  
> as  either "founded" or "unfounded"?
> I thought that detail had been discussed previously and had been  
> resolved:
> http://lists.w3.org/Archives/Public/public-html/2008Sep/0457.html
> In order to make progress on this issue, it would be good to declare  
> this point one way or the other.

One thing I've recommended before is that we require the headers  
attribute to only reference cells before themselves (the referenced  
cell has to make sense as a header cell for the referencing cell). In  
terms of document conformance this could be confined even tighter. In  
terms of processing conformance, UAs must only process headers  
attributes that reference prior cells in tree order. All other headers  
attribute values must be ignored (i.e., those referencing cells that  
follow in tree order). We could also add that headers cannot reference  
cells in the tfoot element for completeness.

With these rules, there is no possibility of a circular referencing of  
header cells. The author may accidentally include such circular  
references, but by ignoring references that follow the referencing  
cell, the error-handling is determined completely.

Take care,
Received on Tuesday, 25 November 2008 15:32:07 UTC

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