W3C home > Mailing lists > Public > www-style@w3.org > May 2012

Re: [css3-mediaqueries] "not", "only" and "and" as media_type

From: Florian Rivoal <florianr@opera.com>
Date: Fri, 25 May 2012 15:59:36 +0200
To: "WWW Style" <www-style@w3.org>, "Kang-Hao (Kenny) Lu" <kennyluck@csail.mit.edu>
Message-ID: <op.wevahmy14p7avi@localhost.localdomain>
The spec does indeed call for B. I'd be tempted to say that
we should leave it as is, as B is a relatively sane behavior
given the situation, but since nobody implements it this
way, maybe we should question that.

I am not a huge fan of A. From an authors' point of view, I would expect  
that either 'only', 'and' and 'not' are all valid names for media types  
that happens to never match, or the three of them are invalid.

The only reason to justification for A is ease of implementation,
and that's likely to go way over most authors's head, so they'll
never remember what's valid and what's not.

  - Florian


On Tue, 22 May 2012 22:47:31 +0200, Kang-Hao (Kenny) Lu  
<kennyluck@csail.mit.edu> wrote:

> My reading of the current grammar
>
>   # media_query
>   #  : [ONLY | NOT]? S* media_type S* [ AND S* expression ]*
>   #  | expression [ AND S* expression ]*
>   #  ;
>   # media_type
>   #  : IDENT
>   #  ;
>
> suggests that "not", "only" and "and" can be used as media_type and
> therefore the following are all valid: "not and (width)", "not not",
> "not and and (width)". However, no browser implements this. Here are
> some options:
>
> A. Change the spec: "not" and "only" as media_type cannot be valid
> unless it's preceded by "not" or "only".
>
> == valid ==
> and [ and (expr) ]*
> [ not | only ] [ not | only | and ] [ and (expr) ]*
>
> == invalid ==
> [ not | only ] [ and (expr) ]*
>
> Firefox12 and IE9 implement this. I probably support this. If we had
> started writing this section using a state machine-based instead of a
> rule-based approach, we would have been closer to this, I think.
>
> I think I support this. The concrete proposal is to change
>
>   # media_query
>   #  : [ONLY | NOT]? S* media_type S* [ AND S* expression ]*
>   #  | expression [ AND S* expression ]*
>   #  ;
>   # media_type
>   #  : IDENT
>   #  ;
>
> to
>
>   | media_query
>   |  : [ONLY | NOT] S* media_type S* [ AND S* expression ]*
>   |  | media_type_no_keywords S* [ AND S* expression ]*
>   |  | expression [ AND S* expression ]*
>   |  ;
>   | media_type
>   |  : IDENT
>   |  ;
>   | /*
>   |  * There is a constraint on it that it must not be {O}{N}{L}{Y} or
>   |  * {N}{O}{T}
>   |  */
>   | media_type_no_keywords
>   |  : IDENT
>   |  ;
>
> B. Don't change the spec (besides perhaps add some test cases to the
> test suite)
>
> == valid ==
> and [ and (expr) ]*
> [ not | only ] [ not | only | and ] [ and (expr) ]*
> [ not | only ] [ and (expr) ]*
>
> == invalid ==
>
> This is actually implementable (I have a patch for Gecko[1], though the
> code is admittedly quite crappy.).
>
>
> C. Change the spec: "not", "only" and "and" cannot be media_type.
>
> == valid ==
>
> == invalid ==
> and [ and (expr) ]*
> [ not | only ] [ not | only | and ] [ and (expr) ]*
> [ not | only ] [ and (expr) ]*
>
> Chromium nightly and Opera12alpha implement this. I am slightly opposed
> to this because, for the majority of normal cases, an extra check to see
> if it's "and" is required.
>
>
> I should note that while some of these are only observable via CSSOM,
> the ones starting with "not" can be observed without scripts, say:
>
> data:text/html,<style>@media not not {:root{background: green;}}</style>
>
> data:text/html,<style>@media not and and (width) {:root{background:
> green;}}</style>
>
> [1] https://bugzilla.mozilla.org/show_bug.cgi?id=757554#c3
>
>
> Cheers,
> Kenny
Received on Friday, 25 May 2012 14:22:36 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 17:20:54 GMT