- From: Ben 'Cerbera' Millard <cerbera@projectcerbera.com>
- Date: Fri, 27 Jun 2008 12:45:16 +0100
- To: "Charles McCathieNevile" <chaals@opera.com>, "Dan Connolly" <connolly@w3.org>, "James Graham" <jg307@cam.ac.uk>, "Ian Hickson" <ian@hixie.ch>
- Cc: "HTMLWG" <public-html@w3.org>, "WCAG 2.0 Comments" <public-comments-wcag20@w3.org>
Dan Connolly wrote: > [...] the current HTML 5 draft allows @headers on td but not on th. > [...] > [...] I can't see any particular reason to use @headers on th [...] Chaals wrote: > [...] There are cases where you have nested headers - i.e. some corner > header will apply to the subheaders (th cells) of a row or column. [...] Heirarchical row headers using <th headers> also exist. There was a thread about these in October 2007: <http://lists.w3.org/Archives/Public/public-html/2007Oct/thread.html#msg159> An example is the second row of data from this table (and others from that website): <http://www.fbi.gov/ucr/05cius/offenses/expanded_information/data/shrtable_02.html> Their exhaustive use of headers+id and scope="col" would be unnecessary on all other cells thanks to good automatic header association. Along similar lines, the "Cash flow statement" table on this page: <http://www.disability.qld.gov.au/budget/06-07/mps/financial.html> The parent row header of each group ends with ":". It uses <th id>. The child row headers within that group point to their parent row header using <th headers>. The rest of the table uses plain <th> and plain <td>, so this mixes the headers+id mode with auto association. James Graham, Simon 'zcorpan' Pieters and I wondered about how to do this. James's algorithm tries to handle it by applying a per-cell exclusion if the headers attribute is present, IIRC: <http://lists.w3.org/Archives/Public/public-html/2008Mar/0075.html> There are also tables which use <td scope> and expect it to work. Partly because HTML4 advises mixed-purpose cells to use <td>, as Steve Faulkner pointed out. FWIW, this falls under the "allow both to be mixed" aspect of how I think we should be approaching accessibility: <http://lists.w3.org/Archives/Public/public-html/2007Aug/0003.html> I sent a message in April 2008 querying limitations in the improved (aka "cleverer") association algorithm which was added to HTML5: <http://lists.w3.org/Archives/Public/public-html/2008Apr/0727.html> The header association algorithm for HTML5 is here: <http://www.whatwg.org/specs/web-apps/current-work/multipage/tabular.html#header-and-data-cell-semantics> Ian Hickson promptly responded, saying a burred line between data cells and header cells would make tables too confusing for authors and "really wasn't worth it": <http://lists.w3.org/Archives/Public/public-html/2008Apr/0743.html> The impression I got from my research is that authors are already making tables which blur this line (or are oblivious to it): <http://sitesurgeon.co.uk/tables/> Ian used whilst doing his own, more extensive research on these issues: <http://lists.w3.org/Archives/Public/public-html/2008Mar/0215.html> For the most part, the current algorithm looks like it does a good job of figuring out what should be associated with what. The way forward, imho, is: * Continued research into making as many of these work as possible. * Requiring small and simple markup from authors of new tables. * Supporting existing tables. * Really bad legacy tables (such as those which use <td> for everything with neither scope nor headers+id) may need a few changes to work (such as using <th> for their header cells) but this should be minimised where possible. * Prototype implementations. * Iterate through ideas and prototypes. * Assess successes and failures. * Describe it precisely in a sane amount of spec text. Perhaps it's impossible to tick *all* the boxes on that list. But I'd like to keep trying. Mozilla are sponsoring me to do more work on this and other issues: <http://projectcerbera.com/blog/2008/05#day29> At the moment, I'm re-organising and rationalising my websites. Once that is done, you can expect more noise from me. :) (I'm not sure when a message is supposed to be hooked up with Tracker.) -- Ben 'Cerbera' Millard <http://projectcerbera.com/me/>
Received on Friday, 27 June 2008 11:46:10 UTC