- From: Gez Lemon <gez.lemon@gmail.com>
- Date: Tue, 25 Nov 2008 17:58:33 +0000
- To: "Robert J Burns" <rob@robburns.com>
- Cc: "Laura Carlson" <laura.lee.carlson@gmail.com>, joshue.oconnor@cfit.ie, "Al Gilman" <Alfred.S.Gilman@ieee.org>, "Janina Sajka" <janina@a11y.org>, "Michael Cooper" <cooper@w3.org>, "HTML WG" <public-html@w3.org>
2008/11/25 Robert J Burns <rob@robburns.com>: > 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. I think we need to consider the purpose of headers before solving problems that may not exist. The purpose of the attribute is to specify the headers for a particular cell so that they can be queried by a user or announced to provide context when the user navigates along a particular axis. When the user queries the cell, only the headers pointed to by the headers attribute should be announced. The fact that the headers themselves may have headers is irrelevant; they would only be required if the user navigates to the header cell, and request headers for that cell. If that wasn't the case, any chained header would result in irrelevant information being announced to the user. I think it's sufficient to say that cyclic references for headers is illegal, without defining rules to prevent something happening that couldn't happen. I think the confusion arises from the phrase, "This seems to some degree to be unfounded". Concerns about cyclic references causing problems in implementations are either founded or unfounded. I can't think how cyclic headers could cause a problem with implementations, but maybe someone has? Cheers, Gez -- _____________________________ Supplement your vitamins http://juicystudio.com
Received on Tuesday, 25 November 2008 17:59:10 UTC