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 10:09:26 +0200
Message-ID: <426F48B6.2010208@re.be>
To: David Woolley <david@djwhome.demon.co.uk>
CC: www-style@w3.org

David Woolley wrote:
>>I can't see why. In the example the lines would always be in proportion
>>to the font. If you use absolute measures, increasing the font size could
>>make the lines overlap. Perhaps there is a catch you might care to explain.
> Overlapping is exactly what happens if you, like most people who use
> line-height, use anything except pure numbers.  If you use em sizes,
> the line height is only correct for the font size on the element for
> which the line-height property was applied.  If you use 1.2, as does
> the specimen style sheet the CSS specification, the line height is
> proportional even if the font size is changed in a sub-element (possibly
> by another style sheet). 

I understand that now. However, that doesn't change the fact that the line
height could be made symbolic and that other rules could be expressed in
terms of it. This is true for other values as well. You seem to count on the
fact that design tools will fix the problem, but you should realize that
such tools are not used by everybody.

>>Well, that is what grammars are for, isn't it? They are with us since quite
>>a while now.
> 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?

>>Absolutely not. If you want to keep the text in phase, you must make sure
> I would say that was well beyond the scope of CSS.  It will break as soon
> as another style sheet intervenes.  CSS should be designed on the basis that
> you are not the only person controlling the layout.  If you want absolute
> control, please use tagged PDF instead.

That is a very easy way to get rid of the matter. How can you just say like
that which typographic aspect is in or out of the scope of CSS? On what is it
based? The construct I have used as an example (remember!) will not break
any faster than other style features. At design time one can work out fall
back solutions.

I should remind you that CSS has a print media type. It is normal to expect
better quality on paper. This part of CSS does not get the proper attention.

>>If every proposed feature is going to be rejected purely on the basis of
>>browsers being immobile, then why bother with CSS3 at all? On this list
> It is a fundamental design principle of CSS that new features should not
> prevent older browsers from interpreting the parts of the style sheet they
> understand.  It also ought to be a fundamental design principle of "web
> designers" to ensure that, for example by preceding a rule for a new feature
> with a fall back rule, that their designs also exhibit that backwards 
> compatibility.

This is all very true, but can you point out how the proposed constants
feature violates these principles?
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 08:09:32 UTC

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