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CSS constraints

From: Jason White <jasonw@ariel.ucs.unimelb.EDU.AU>
Date: Mon, 6 Oct 1997 09:09:18 +1000 (AEST)
To: WAI HC Working Group <w3c-wai-hc@w3.org>
Message-ID: <Pine.SUN.3.95.971006084248.14756A-100000@ariel.ucs.unimelb.EDU.AU>
Following Al's example, I wish to make explicit the constraints which I
take to be fundamental in proposing enhancements to the CSS 2
specification. These constraints apply both to the table reading issue and
to the tree transformation properties which I have proposed.

1. CSS syntax does not permit the use of variables, the construction of
loops or the conditional execution of commands. Perhaps the @MEDIA rule
can be regarded as amounting to a limited form of conditional statement,
but in general, such constructs are unavailable.

2. The concept of applying style properties to selected elements of a
document is fundamental to CSS 2, as is the basic syntax of selectors and
style properties.

3. The existing range of selectors and style properties, as defined in the
current CSS 2 draft, is, so far as possible, to remain unmodified,
although the WAI may propose such changes (if any) that are deemed
necessary for the purpose of ensuring accessibility. Extensions can
however be proposed with a greater degree of freedom, provided that they
can be justified as desirable for the purpose of enhancing the formatting
of documents in braille, audio or other media (such as text-only displays)
that are of importance to people with disabilities.

My tree transformation proposal fully respects the foregoing limitations,
since it envisages that the transformation properties would be applied to
elements which are to be selected on the basis of their CLASS and ID
values, in accordance with CSS syntax. The transformations are to be
applied sequentially throughout a document in the order in which the
transformation rules appear in the style sheet.

My suggestion for adding style properties to facilitate the audio
rendering of tables, modifies CSS syntax to the extent of permitting
commands to be embedded in text strings, whereby reference to the cells of
a table can be made. The essence of the proposal, however, does not rely
on this extension and could be implemented without it, albeit less
elegantly. It should be noted that in the current CSS 2 draft, the
sections on generic prefix/suffix text and numbering, two of the areas
which are high on the WAI agenda, are simply "place holders" and do not
contain any substantive material.
Received on Sunday, 5 October 1997 19:09:41 UTC

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