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Re: Heuristic Tests for Data Tables (Discussion)

From: James Graham <jg307@cam.ac.uk>
Date: Tue, 04 Sep 2007 18:43:00 +0100
Message-ID: <46DD9924.6000802@cam.ac.uk>
To: Robert Burns <rob@robburns.com>
CC: Ben 'Cerbera' Millard <cerbera@projectcerbera.com>, Philip Taylor <philip@zaynar.demon.co.uk>, HTMLWG <public-html@w3.org>

Robert Burns wrote:
> Hi James,
> 
> 
> On Sep 4, 2007, at 7:13 AM, James Graham wrote:
> 
>>
>> James Graham wrote:
>>> James Graham wrote:
>>>>
>>>> Ben 'Cerbera' Millard wrote:
>>>>> I wonder how many tables can be made natively accessible? How many 
>>>>> will need to be retrofitted by authors with <th> or scope="" or 
>>>>> headers="" and how likely is that? I guess more studying (like 
>>>>> Philip and I and others have done) and prototyping of 
>>>>> implementations (like James Graham might do)
>>>>
>>>> There's some very early work on this available at [1] (only the 
>>>> HTML4 algorithms are currently implemented). Due to a bug in a 
>>>> html5lib serializer badness occurs when you give it a page 
>>>> containing more than one table. I also haven't checked that it's 
>>>> giving the correct results in almost any cases. However if you want 
>>>> to report bugs feel free.
>>> This now also has some work on the algorithm from the HTML 5 spec, 
>>> with similar caveats as before i.e. it is hideously under tested.
>>
>> I have now moved the table inspector to [1] and added an 
>> "experimental" option which is currently based on the HTML 4 algorithm 
>> with some improvements:
>>
>>  * Optionally treats <td><strong> and <td><b> as headers
>>  * Ignores headers with @scope set when looking for implicit headings 
>> (to see why this is important look at the "Day 2" cell in [4]).
> 
> Its looking good. However, I'm not clear what you mean by this "Ignores 
> headers with @scope set..."  Even when looking at "Day 2" cell its still 
> not clear to me. Could you say a little more about what you mean.

Imagine a table structure like the following

th           1    |   td   2
th scope=row 3    |   td   4
td           5    |   td   6

The question is which headers apply to the td cell 5? It doesn't have any 
heading information set from explicit scope or headers attributes so we fall 
back on the implicit algorithm. Per HTML 4 the implicit algorithm searches up 
the column and marks heading cells as headers of cell 5. The "algorithm" given 
in the HTML 4 spec isn't clear about how the presence of @scope affects this 
association. My initial reading was that @scope is not considered so both cells 
1 and 3 are considered headings for cell 5, whereas excluding cells with @scope 
set, only cell 1 is a heading for cell 5. Reading again, I suppose "Then search 
upwards to find column header cells" is supposed to be taken to exclude headings 
with scope="row[group]" set, which I didn't pick up on when I first implemented 
this, but did change in the experimental version. This is another example of why 
the spec has to be precise in its UA requirements if we want interoperable 
behavior, even though that precision will make sections of the spec less 
accessible to authors.

-- 
"Eternity's a terrible thought. I mean, where's it all going to end?"
  -- Tom Stoppard, Rosencrantz and Guildenstern are Dead
Received on Tuesday, 4 September 2007 17:43:29 GMT

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