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[css3-writing-modes] a third option for implementing logical properties

From: L. David Baron <dbaron@dbaron.org>
Date: Thu, 21 Oct 2010 12:35:56 -0700
To: www-style@w3.org
Message-ID: <20101021193556.GA19023@pickering.dbaron.org>
I wanted to raise a third option for how to deal with logical
properties in addition to the two I cited in
http://lists.w3.org/Archives/Public/www-style/2010Jun/0003.html .

The proposal now in
http://dev.w3.org/csswg/css3-writing-modes/#logical-prop requires
strict adherence to CSS cascading rules.  An implementation can do
this using the approach described in
http://lists.w3.org/Archives/Public/www-style/2002Sep/0049.html .

However, if we allow implementation-defined deviation from the CSS
cascading rules when determining the relative priority of
declarations of a logical and physical property **in the same
ruleset**, then I think the required implementation complexity is
significantly reduced.  (If we did this, I would suggest making use
of such property pairs within the same ruleset an authoring
conformance error.)

In particular, with this approach, implementations would no longer
need the extra pseudo-properties to track the relative priority of
declarations within the same declaration, and they could do the
relevant computations at cascade time after determining the
direction.

(Getting this reduction in complexity might somewhat limit
implementation approaches, since it requires computing 'direction'
before cascading any properties with logical/physical pairs.  I
think that's not a problem in Gecko, so this approach would simplify
our implementation of logical properties significantly.  I'd be
interested to hear if it would help in other implementations.)

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Thursday, 21 October 2010 19:36:31 GMT

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