- From: Jason White <jasonw@ariel.ucs.unimelb.edu.au>
- Date: Fri, 16 Apr 1999 14:12:35 +1000 (AEST)
- To: WAI Markup Guidelines <w3c-wai-gl@w3.org>
It should also be remembered that the priorities and checkpoints are based on what is needed for access (at different levels of accessibility), and that convenience or otherwise for content developers is not a relevant consideration except in so far as a choice needs to be made between two or more strategies that are equally advantageous from the standpoint of access, but which can not be implemented with equal ease or convenience, in which case the the more practicable solution is to be preferred. Thus, questions pertaining to the likely effect of guidelines concerned with tables on developer acceptance of the guidelines should not influence the decisions of the working group, which must be made on principled grounds, based on the definitions of priorities as given in the document itself and also on the access barriers which layout tables create. This is why there is a rather strictly defined set of circumstances in which layout tables can be used, without requiring generation of an alternative, structurally and semantically rich, version of the document, namely those conditions under which the structure and content are adequately reflected in the markup and the tables are not acting as a substitute for other markup constructs, but only as a kludge to force a particular rendering by visual user agents. By avoiding TH, CAPTION, and other such elements in layout tables, a user agent can distinguish between layout and data tables. Furthermore, the single column requirement avoids problems in respect of primitive screen readers (I might be wrong of course, but it still seems to me that there would be a significant constituency of screen reader users who would find multi-column tables problematic without the wide availability of linearisation software). A formulation similar to the following might be appropriate (comments are welcome): "5.3: Avoid using tables for layout unless the required formatting effects can not be achieved with style language features supported by user agents. (Priority 2). [Note discussing the evolution of style sheet positioning and the anticipated implementation of this capability by user agents, and pointing out that layout tables constitute an abuse of HTML markup as defined in W3C Recommendations on HTML.] 5.4 If tables are used for layout, (a) do not use TH cells to produce special font effects; this will also enable screen readers, braille or speech-based browsers, etc., to distinguish layout tables from those which contain genuine tabular information. (b) Ensure that within the table cells, correct markup is used to convey the structure of the document (including headings, paragraphs, lists, etc.), and that an appropriate reading order would be preserved if the table were linearized. See also checkpoints 3.2, 3.3 and 3.4. Priority 2 Note: Some screen readers can not decolumnize tables. It is therefore necessary to avoid the use of layout tables, or provide an alternative page, if a multi-column format is desired. See checkpoint 10.3." In the glossary, definition of linearization as applied to tables: ignoring table-related markup, etc.
Received on Friday, 16 April 1999 00:12:42 UTC