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Re: A possible presentational hints proposal for CSS 2.1

From: Chris Lilley <chris@w3.org>
Date: Tue, 8 Oct 2002 20:21:33 +0200
Message-ID: <19305369953.20021008202133@w3.org>
To: www-style@w3.org, Stuart Ballard <sballard@netreach.com>
CC: Ian Hickson <ian@hixie.ch>, Rijk van Geijtenbeek <rijk@iname.com>

On Tuesday, October 8, 2002, 6:37:51 PM, Stuart wrote:


SB> Chris Lilley wrote:
>> On Tuesday, October 8, 2002, 5:28:07 PM, Stuart wrote:

>> SB> May I suggest including language that allows other XML vocabularies to 
>> SB> explicitly designate attributes as presentational if they want to?
>> 
>> 
>> Such as, for example, languages that are themselves presentational?
>> That would be a lot better than merely looking at HTML and deciding
>> that all XML has no presentational attributes.
>> 
>> Rather than talk about 'transitional phases' and so forth, i suggest:
>> 
>> a) distinguishing between presentational and non-presentational XML
>> grammars. For example, MathML has two grammars, one of each type.
>> 
>> b) stating that non-presentational grammars should not have, or add,
>> presentational attributes.

SB> Unfortunately, as you point out later, this doesn't fit with several 
SB> already-existing XML vocabularies.

I'm not sure that I do - which ones were you thinking of that were
a) in XML
b) were not presentational
c) had presentational attributes?

>> c) stating that presentational attributes should have the exact same
>> name, syntax, and semantics as the corresponding property. They then
>> become zero-specificity "default styling" which is readily "restyled"
>> by any CSS selector. this is, for example, the case in CSS.

SB> I'm not sure that all attributes in classic HTML can be shoehorned into 
SB> this rule. Are you?

Since classic HTML is not XML, whatever it does or does not do is not
relevant to this part of the discussion. But, I would assert (since
you ask) that classic HTML does none of the three things that I
suggested:

- it does not clearly distinguish between presentational and non
presentational, claims to be one and is pretty much exclusively
focused on the other.

- the 'grown, not designed' attributes and elements atre mainly
distinguished by not being the same as the corresponding properties in
name, or allowed syntax, or presentational effect; neither one to one
nor by a simple mapping.

Further, it is experience with the messy failure to do these things
that motivates my list.

I was thinking primarily of XSL and of SVG when writing the list;
MathML does some of it and fails some of it.

>> While being more realistic and less antagonistic to other W3C
>> specifications, this approach also - by encouraging use of stylistic
>> attributes, rather than the style attribute, for presentational
>> grammars - encourages restylability. Currently, lots of tools that
>> construct content incrementally spit out xml elements with style
>> attributes on each element. Due to the high specificity of the style
>> attribute, this makes later restyling hard in CSS2 and impossible in
>> CSS 2.1

SB> I agree with this reasoning, but I'm not going to go into it because 
SB> it's a tangent from the issue at hand.


I see them as closely related; the effect of what one spec does on
what another spec does, or on what implementations do, cannot be
ignored.

SB> I hope that the W3C eventually agrees with this and comes up with
SB> a solution, though :)

Yes. Working on it.

>> Presentation attributes are not just a legacy issue.

SB> Point.

>> SB> Thus, I'd suggest treating XHTML Transitional as
>> SB> HTML,
>> 
>> No!! Its XML, uses the XML Object Model, etc. Don't muddy things
>> further by treating some XML as HTML.

SB> I meant "in the same way as the proposal currently treats HTML", not 
SB> "pretend that it *is* HTML".

Ah - okay.

>> SB>   For other XML languages where the document type or schema
>> 
>> or namespace (for namespace qualified attributes)

SB> Point.

>> This is where I really wish that the presentation attributes in XSL
>> (and in SVG) had been defined in their own namespace. I still think
>> that would have been a better solution.

SB> I agree, but since they're not, we need a solution for those existing 
SB> specs.

To be clear - I proposed this, but it was not accepted. I was just
noting in passing that it would have made the 'unknown XML grammar'
case more tractable; attributes that are namespace qualified are
easier to deal with than anonymous attributes in the element
partition, that might or might not be the same as similarly named
attributes in a different element partition.

SB> And, of course, for XHTML Transitional, which falls into the same 
SB> category (some presentational and some semantic attributes).

SB> I think my language (with your specific proposed additions, such as the 
SB> namespace issue) could cover MathML, XSL-FO and SVG perfectly well.

Probably. I would need to see it all as one piece of text rather than a
series of diffs to be sure, but I agree its likely that it would.

SB>  In
SB> fact, the treatment of classic HTML (and what I proposed for XHTML 
SB> Transitional) is really just part of the same thing, except that the use 
SB> of CSS with HTML is so ubiquitous that it makes sense for the CSS 
SB> authors to explictly list the presentational attributes for that language.

Perhaps.

SB> The only difference is that now the treatment of presentational 
SB> attributes is no longer just a legacy issue, but since the proposed 
SB> language never mentioned "legacy" at all, the bulk of it still stands.

Point taken.




-- 
 Chris                            mailto:chris@w3.org
Received on Tuesday, 8 October 2002 14:22:00 GMT

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