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Re: [css21] @import parsing

From: Bert Bos <bert@w3.org>
Date: Tue, 10 Mar 2009 18:16:21 +0100
To: www-style@w3.org
Message-Id: <200903101816.21827.bert@w3.org>
Maybe it's useful to write down why @import is the way it is, because 
that probably hasn't been written down anywhere yet. It may help to 
decide in the future what can come before an @import and what can't.

The @import was designed using two principles (which in turn were meant 
to make it as easy as possible for users to remember how CSS worked):

1) The meaning of the rules in the imported style sheet doesn't depend 
on where the @import is called from. The caller only determines whether 
the style sheet is imported or not. Thus the caller (whether HTML or 
CSS) may attach conditions, such as Media Queries, but it may not 
change the meaning of any keyword or construct in the imported style.

2) Any rule in an imported style sheet can be overridden by a rule with 
the same specificity in the importing style sheet, but never the other 
way round.

These rules are reminiscent of the import statements in Java or Modula, 
but different from the #include of C. (The #include of C has 
more "power" in theory, but the principle of least power applies here, 
and import is easier to understand.)

However, to make sure that people who have the C model in their mind are 
not confused, we arranged the syntax so that there is no difference 
between import and include, namely by making the @import always the 
very first thing in the style sheet. So it doesn't matter if you think 
of @import as a macro, as in C, the eventual result of the style sheets 
happens to match that mental model as well.



Bert
-- 
  Bert Bos                                ( W 3 C ) http://www.w3.org/
  http://www.w3.org/people/bos                               W3C/ERCIM
  bert@w3.org                             2004 Rt des Lucioles / BP 93
  +33 (0)4 92 38 76 92            06902 Sophia Antipolis Cedex, France
Received on Tuesday, 10 March 2009 17:16:59 GMT

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