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Re: [CSS 2.1] @charset, @import, and error recovery

From: L. David Baron <dbaron@dbaron.org>
Date: Fri, 7 Mar 2008 20:46:26 -0800
To: Justin Rogers <justrog@microsoft.com>
Cc: "www-style@w3.org" <www-style@w3.org>
Message-ID: <20080308044625.GA9348@ridley.dbaron.org>

On Saturday 2008-01-26 16:58 -0800, Justin Rogers wrote:
> > > Browsers are inconsistent here.
> 
> > How?
> 
> 
> I've given an example below. I've messed up two charset rules supplied
> a bogus page and media, given a valid import (a.css which is DIV {
> color: purple }), followed by an invalid one, followed by another
> valid one (c.css which is DIV { color: green; })...

Sorry to have dropped this one on the floor for a while.

> @charset "utf-8" foo bar baz;
> @charset "utf-8" foo bar baz;
> @page { }
> @media { }
> @import url(a.css);
> @import url(b.css) foo bar;
> @import url(c.css);

There's a problem with your example.  The @page rule in it is actually
perfectly valid.  Therefore any browser that supports @page should
pretty clearly ignore the @import rules based on the current spec.

So I'm not sure there's as much of an inconsistency as you thought.

Compare the following:
  http://dbaron.org/css/test/2008/import-after-page
  http://dbaron.org/css/test/2008/import-after-pagg
  http://dbaron.org/css/test/2008/import-after-media

In Firefox, the first two are green, since @page is not supported or
parsed.  But the third is black and underlined.  The same is true of
IE7.  This means the ignored @page and @pagg rules are not used to
determine whether to ignore the @import, but the used @media rule is.

In Opera 9.26, the one with @page is black (@import ignored), but the
one with @pagg is green (@import used).  This makes sense since @page is
supported in Opera.

In Safari 3.0.4, all three are black (so there is some inconsistency).


I don't think any clarification to the spec is strictly needed, since 
http://www.w3.org/TR/2007/CR-CSS21-20070719/syndata.html#at-rules says:
  # CSS 2.1 user agents must ignore any '@import' rule that occurs
  # inside a block or after any valid statement other than an @charset
  # or an @import rule. 
Note the "any *valid* statement".  This requirement is a conformance
requirement on user agents.

However, there is the statement at
http://www.w3.org/TR/2007/CR-CSS21-20070719/cascade.html#at-import
(which you quoted in the first message in this thread):
  # Any @import rules must precede all other rules (except the @charset
  # rule, if present).
which is a conformance requirement on style sheets.  Perhaps to make
this clearer, we should add "In CSS 2.1," or "In valid CSS 2.1 style
sheets," to the beginning of the sentence.  We could also add an
additional sentence following it saying:
  # See the <a href="syndata.html#at-rules">section on parsing</a> for
  # when user agents must ignore @import rules.

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Saturday, 8 March 2008 04:46:36 GMT

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