W3C home > Mailing lists > Public > www-style@w3.org > April 2005

Re: User constant declarations in style sheets

From: Werner Donné <werner.donne@re.be>
Date: Wed, 27 Apr 2005 11:10:58 +0200
Message-ID: <426F5722.9020303@re.be>
To: Mikko Rantalainen <mikko.rantalainen@peda.net>
CC: www-style@w3.org

I agree that those problems have to be solved and that it would take a
long time for UAs to support it, but that is true for any proposed
change in the syntax. So the criterion is if enough people find it
worthwhile. Any proposed feature will have great difficulty in finding
some momentum if it is dismissed immediately after its posting. When
a proposal is dismissed, the least one can expect is that the given reasons
are to the point.

What about CSS3? In the current culture it will be very difficult as well
for any of it to be adopted.

Mikko Rantalainen wrote:
> Werner Donné wrote:
>> David Woolley wrote:
>>> The key design rule for CSS grammars is backwards compatibility.  All 
>>> new
>>> syntax must result in the new construct being ignored by browsers 
>>> that don't support the new features.
>> If the "lh" in the example would be interpreted as a unit by a browser 
>> that
>> doesn't support the constants feature, the browser would have to 
>> conclude a
>> wrong length was specified and should therefore ignore the rule. What 
>> is so
>> special about it then?
> The problem is that *you* get to define what "lh" means. For example, in 
> your example you defined that
> const lh: 1.2em;
> which means that 2lh is equivalent to 2.4em if I've understood 
> correctly. The point is that *if* this is allowed there's no way to ever 
> define any new unit without requiring UA to support this "const" feature 
> too. For example, W3C couldn't define a new unit "lh" because your 
> already example uses it. If W3C defined lh as anything else but "1.2em", 
> your stylesheet would get broken - that is, unless the UA also supported 
> "const" so it could decipher what your stylesheet really means. UA 
> shouldn't be required to support "const" feature to support all the 
> units defined in the spec.
> The problems that need to be solved:
> 1) How to express contants so that old UA correctly ignore those?
> 2) Does this feature prevent other features in the future?
> 3) How does the cascade work with the user style sheet?
> 4) If user style sheet already defines similarly named constant, what 
> should happen?
> In the end, the question remains: is it really worth the trouble 
> considering that real world UAs would support this feature only after a 
> really long time?

Werner Donné  --  Re BVBA
Engelbeekstraat 8
B-3300 Tienen
tel: (+32) 486 425803	e-mail: werner.donne@re.be
Received on Wednesday, 27 April 2005 09:11:06 UTC

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