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Re: [CSS3-color] Errata

From: Chris Lilley <chris@w3.org>
Date: Wed, 8 Feb 2012 12:02:21 +0100
Message-ID: <1421536926.20120208120221@w3.org>
To: Anton Prowse <prowse@moonhenge.net>
CC: www-style@w3.org
Hello Anton,

This email relates to your mail

This was discussed by the CSS WG

based on that and subsequent informal discussion, I propose the following resolution to the three points you raise. 

Comment 1

We don't see it as confusing (it is indeed, as you suggest, 
trying to explain the origins of the spec and says so explicitly:
"The specification is the result of the merging of relevant parts of the following Recommendations and Working Drafts, and the addition of some new features." This is why the specifications mentioned in that section are non-normative).

We propose to resolve your comment by explicitly stating, in section 1 Introduction, "This section is non-normative".

Comment 2

The wording "Container element" is indeed SVG terminology. The definitions are given in


but to summarise, in SVG elements are divided into two classes: graphics element (which draw stuff) and container elements (whose children may draw, but they themselves do not directly draw). 

There is no such distinction in CSS, but the critical issue is that, when something that has children, and the 'something' has its opacity property set to a non-initial value, you render that something *and its children* as if the opacity was 1, then change the opacity of the whole rendering. You do not render by propagating the opacity separately to all the children.

This is already described in the prose, thus:

"Conceptually, after the element (including its descendants) is rendered into an RGBA offscreen image, the opacity setting specifies how to blend the offscreen rendering into the current composite rendering."

I propose to address your comment by changing 

"If the object is a container element" 


"If the object has children" in the definition of the property value, and then adding, in the descriptive prose, "For SVG, 'has children' is equivalent to being a container element [SVG11]" where 'container element' links to
and [SVG11] links to SVG 1.1 in the normative references.

Comment 3

Your proposed wording isn't quite sufficient because "treated as though it has the index: 0" also has an effect on the painting level of descendents.

Instead, we suggest to address your comment by changing 

"except that ‘auto’ is treated as ‘0’" 


"except that a computed value of 'auto' behaves as if its z-index were zero" 

to make it clear that it doesn't change the computed value.


 Chris Lilley   Technical Director, Interaction Domain                 
 W3C Graphics Activity Lead, Fonts Activity Lead
 Co-Chair, W3C Hypertext CG
 Member, CSS, WebFonts, SVG Working Groups
Received on Wednesday, 8 February 2012 11:05:56 UTC

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