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Re: [css3-mediaqueries] handling of unknown media types

From: Stewart Brodie <stewart.brodie@antplc.com>
Date: Tue, 10 Jun 2008 14:02:08 +0100
To: "Anne van Kesteren" <annevk@opera.com>
Cc: www-style@w3.org
Message-ID: <6a23494e06691324690e1846c5ffe0d150d85e09@localhost>

"Anne van Kesteren" <annevk@opera.com> wrote:

> David Baron has suggested he prefers a different type of error handling  
> for unknown media types. E.g., that 'not foo' evaluates to true and  
> instead of being ignored. This would avoid having to hardcode a specific  
> set of known media types. E.g., if 'not projection' was to evaluate to  
> true as well in user agents not supporting projection. (This would also be
> more in line with existing implementations of Opera and WebKit.)

It does seem more logical to me to have "not" always invert the result of
the evaluation.  That way you can write if-then-else style media queries in

@media foo and (bar) and (baz) { }
@media not foo and (bar) and (baz) { }

and know that exactly one of the two will match.

However, I'm not too bothered - my implementation can handle it easily
either way, as queries are always evaluated ignoring the 'not' and then the
result of the query evaluation (yes, no, invalid) is mapped to a final
"yes/no" answer taking into account any not.

> If we do this I think it would be the first time an unrecognized IDENT  
> ends up in the CSSOM. I'm not really convinced that's a good idea, but I  
> don't feel strongly about it.

It's not even just IDENT tokens: the "3d-glasses" example in the MQ spec is
a DIMENSION - so I have a hack that reserialises DIMENSION tokens when I'm
looking for a media type in the parser.

What is the current status of the CSSOM specification - is the 30 Dec 2007
editor's draft still the latest version?  Currently, I'm using that draft as
guidance to how to expose the media query information through DOM, as that's
the most complete part of the document and it seems sensible to me and
doesn't conflict with DOM L2 Style.

I would like it very much if "example" serialised to "not all", along with
all other invalid queries - it would make my job an awful lot easier and
make the code safer.

Currently, if I don't recognise a media type, currently I do actually store
it as a string, so that I can regenerate it for MediaList.mediaText (DOM L2
and CSSOM).  The MQ spec says things like (examples in section 3): 'When all
media queries in a media query list are ignored, it is the same as if "not
all" was specified.'   Is it talking about evaluation of the MQ only, or the
serialisation too?  Should "example" be serialised as "example" or "not
all"?   Should an invalid feature cause the whole media query to be
discarded and replaced by "not all" for serialisation purposes?  Laying down
the serialisation rules would also make it a lot easier to write testcases,

> Unless more people are opposed I'll try to make this change before the
> telcon tomorrow so we can move forward with this specification again.

I don't mind which way it is, as long as a decision is made and stuck to :)

Stewart Brodie
Software Engineer
ANT Software Limited
Received on Tuesday, 10 June 2008 13:02:49 UTC

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