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Re: Style sheets for access

From: Jason White <jasonw@ariel.ucs.unimelb.EDU.AU>
Date: Sat, 6 Dec 1997 10:25:48 +1100 (AEDT)
To: WAI Interest Group <w3c-wai-ig@w3.org>
Message-ID: <Pine.SUN.3.95.971206100839.16951C-100000@ariel.ucs.unimelb.EDU.AU>
This issue has been discussed before on this list, in the context of media
types. The outcome of those deliberations can be conveniently
recapitulated by contrasting two examples.

1. The user's default style sheet is of type media="aural". In this case,
only subsequent style sheets of type media="oral" will modify the user's
preferences. This is a desirable outcome, for it allows the author, should
he or she wish to do so, to exercise control over the audio rendering,
with the default being supplied by the user.

2. The media type of the user's default style sheet is a parameterized
value, for instance a hypothetical media type of media="screen enlarged",
which is not presently defined in any specification but which, for the
sake of illustration, may be regarded as designating a style sheet which
establishes a large font and perhaps a particular colour scheme. Now there
are two ways in which subsequent styles of the same base type, in this
scenario they would be of type media="screen", could be treated: (I) they
could be ignored; (II) they could participate in the cascade and thus
override the provisions of the default style sheet of type media="screen
enlarged".

Now it was generally agreed, in our previous treatment of this topic, that
behaviour (II) should be preferred. It was argued that, for example, it
would be absurd if the provisions of a default style sheet of type
media="braille embossed 40" could not be modified by a style later in the
cascading order of type media="braille". However, as the example of large
fonts indicates, there are cases in which behaviour (I) as enumerated
above would be the preferable option, thereby preventing style sheets of
type media="screen enlarged" from being subject to later styles of type
media="screen".

One solution might be to introduce a directive into CSS which, if present
in a style sheet, indicates that only subsequent styles which match the
media type exactly will participate in the cascade. Thus, in the default
style sheet of type media="screen enlarged", the proposed directive would
be included. Any later style sheet of type media="screen" would, pursuant
to this directive, be excluded from the cascade, since it would not
exactly match the media type of "screen enlarged". A fortiori, any later
style of type media="screen enlarged", whether supplied by the user or the
author, would match and would thus participate in the cascade.
Received on Friday, 5 December 1997 18:26:10 GMT

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