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Re: [css3-mediaqueries] Malformed media query error handling

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 27 Apr 2012 09:22:58 -0700
Message-ID: <CAAWBYDA8TCdG6snr9co4AVm6YDOz37FAFD+rY+MDqtuUZLomMQ@mail.gmail.com>
To: Vasily Stepanov <vasily.stepanov@gmail.com>
Cc: www-style@w3.org
On Fri, Apr 27, 2012 at 1:49 AM, Vasily Stepanov
<vasily.stepanov@gmail.com> wrote:
> According to error handling, described in section 3.1:
> User agents are to handle unexpected tokens encountered while parsing
> a media query by reading until the end of the media query, while
> observing the rules for matching pairs of (), [], {}, "", and '', and
> correctly handling escapes.
> There is an example for this case:
> @media (example, all,), speech { /* only applicable to speech devices */ }
>
> CSS21 says the following in section 4.1.5: An at-rule consists of
> everything up to and including the next semicolon (;) or the next
> block, whichever comes first.
>
> Consider this malformed CSS example:
> @media {example, all,}, speech { /* only applicable to speech devices */ }
>
> () block from the previous example has been replaced with {} block.
>
> So it is unclear how should I parse this malformed CSS.
>
> According to CSS21 I have to parse it like this:
> @media { /* error while parsing rulesets */ }
> /* error while parsing selectors */
>
> According to css3-mediaqueries I have to parse it like this:
> @media /* error while parsing media query */ speech { /* ... */ }

Simon is correct in both his examples - your "CSS21" interpretation is
the right behavior.

I agree that this isn't perfectly clear from the MQ spec - a basic
disadvantage of relying purely on grammar-based error handling.  This
will be tightened up in the future by the Syntax module.  The parser
shouldn't attempt to validate the @media rule until it has been
closed, which happens after the first } in your example.  The stuff
following that first } will parse as a Rule instead, with a selector
of ", speech", and thus will also be ignored.

~TJ
Received on Friday, 27 April 2012 16:23:48 GMT

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