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Re: [CSS2.1] Replaced elements

From: Bert Bos <bert@w3.org>
Date: Tue, 13 Sep 2005 16:57:33 +0200
To: "Staffan Mhln" <staffan.mahlen@comhem.se>
Cc: www-style@w3.org
Message-Id: <200509131657.33583.bert@w3.org>

On Wednesday 10 August 2005 18:28, Staffan Mhln wrote:
> > On Wednesday 2005-06-15 18:24 +0200, Staffan Mhln wrote:

> > > Whats the reason for choosing the approach that the CSS renderer
> > > needs to be aware of a ratio rather than that the embedded media
> > > needs to be made aware of the CSS constraints?

The CSS WG discussed your suggestion and decided not to change the 
algorithm in CSS 2.1. There may be room for other algorithms in CSS3, 
but that needs investigation, probably in cooperation with the CDF WG.

Defining how to treat replaced objects with a known aspect ratio is an 
improvement over the previous situation. There are more defined cases 
now than before. (In particular the case of SVG without an intrinsic 
size but with a fixed aspect ratio.) And we are pretty confident that 
there will be good interoperability on this algorithm.

In the case of SVG, the CSS and SVG WGs actually had a joint meeting on 
this topic last March and the result was the algorithm that is now in 
CSS 2.1. Width, height and aspect ratio is all that an SVG graphic can 
contain. There is simply no more information available.

There are objects (HTML+CSS documents in particular) that have complex 
relations between width and height. In general in such cases we don't 
want to wait for a plug-in to compute the width from the height or vice 
versa. In CSS 2.1, such replaced elements will simply get a fixed 
height.

Transcluding HTML in HTML seamlessly, without a scrollbar, is a topic 
that needs investigation: is it needed? is XInclude a better solution? 
or SSI? what other properties than width/height would apply to the 
transcluded object? does it inherit properties?

It is something the CSS WG and the CDF WG will have to discuss together. 
If some new model is defined for that case, it is likely to not only 
affect style, but also other things (can you tab to a button in the 
nested document? can a form be partly in the container and partly in 
the nested document? if the embedding is seamless, then what about 
copyright or security?).

Your approach (don't ask the plug-in for its size, but enter a 
negotiation until the plug-in and the container agree) is useful input 
to that discussion. It is not an unknown technique (the X Window System 
uses it to negotiate between a window manager and an application), but 
it is new on the Web and thus not suitable for CSS 2.1.



Bert
-- 
  Bert Bos                                ( W 3 C ) http://www.w3.org/
  http://www.w3.org/people/bos                               W3C/ERCIM
  bert@w3.org                             2004 Rt des Lucioles / BP 93
  +33 (0)4 92 38 76 92            06902 Sophia Antipolis Cedex, France
Received on Tuesday, 13 September 2005 14:57:47 GMT

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