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Re: Proposal of @ua

From: Andrew Fedoniouk <news@terrainformatica.com>
Date: Tue, 27 Nov 2007 12:00:01 -0800
Message-ID: <474C7741.8000908@terrainformatica.com>
To: Todd Russell <groovechicken@gmail.com>
CC: www-style@w3.org

Todd Russell wrote:
>> I suggest to add support(attribute[,value]) function instead.
>>
>> So this:
>>
>> @media screen and has(renderer:Trident)
>> {
>>   a.exlink {display:inline-block;}
>> }
>>
>> can be rewritten as
>>
>> @media screen and support( display, inline-block  )
>> {
>>   a.exlink {display:inline-block;}
>> }
>> @else
>> {
>>   a.exlink {display:block; }
>> }
>
> Sorry to butt in, but I couldn't help noticing something obvious.  
> Forgive me if this has been discussed already as I am new around here.
>
> Why not the following?:
>
> @media screen and
> {
>     a.exlink {display:inline-block;}
> }
> @else
> {
>     a.exlink {display:block; }
> }
>
That will complicate things significantly. Parsing errors handling is 
established already. Say someone will try to use our flex units:

@media screen and
{
    a.exlink { width :2*;  }
    p { width :200px;  }
}
@else
{
    a.exlink { width :200px;  }
}

CSS mandates that height :2*; has to be ignored until closing ';' if UA 
does not recognize such units.
And it makes sense. Also I believe that almost all CSS parsers establish 
attribute only parsing context.
It would be difficult to redesign such parsers to support rollbacks of 
sets of attributes.

As in our case flex units makes sense only if UA support layout manager 
module (it uses, say, 'flow' attribute)  then we can write this as

@media screen and support(flow)
{
    a.exlink { width :2*;  }
    p { width :200px;  }
}
@else
{
    a.exlink { width :200px;  }
}

and this will work.

Typical implementation of support(flow) can be table-driven in UA's 
source code thus pretty reliable and straightforward - good chance that 
it will reflect actual set of supported attributes and features.

Andrew Fedoniouk.
http://terrainformatica.com
Received on Tuesday, 27 November 2007 20:00:24 GMT

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