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[CSS21] Issue 4: Clarification Needed: Default Media Type if None Specified [DRAFT2]

From: Gregory J. Rosmaita <oedipus@hicom.net>
Date: Tue, 18 Dec 2007 03:25:38 +0000
To: wai-xtech@w3.org
Message-Id: <20071218032436.M68708@hicom.net>

[Reviewer's Note: this post refers to the Candidate Recommendation draft 
of CSS 2.1,
http://www.w3.org/TR/2007/CR-CSS21-20070719
comments upon which are due by 20 December 2007]


In the CSS2.1 section on media types, it explicitly states:

<q 
src="http://www.w3.org/TR/CSS21/media.html#media-types">
Media types are mutually exclusive in the sense that a user 
agent can only support one media type when rendering a 
document. However, user agents may use different media types 
on different canvases. For example, a document may 
(simultaneously) be shown in 'screen' mode on one canvas and 
'print' mode on another canvas. 

Note that a multimodal media type is still only one media 
type. The 'tv' media type, for example, is a multimodal 
media type that renders both visually and aurally to a 
single canvas. 
</q>

Which undermines the argument that the @media all rule applies when no 
specific media type is specified; however, it has been made plain -- at 
least in email form -- from the editors of the CSS 2.1 draft -- that the 
@media all rule DOES apply when no specific media type is specified; 
consult:

<http://lists.w3.org/Archives/Member/wai-liaison/2007May/0023.html>

as Al Gilman, WAI PF's chair, pointed out during this exchange, in the 
Visual Formatting Model section, the display property is explicitly 
defined as pertaining to all media types, and yet, in the definition of 
the none value for the display property is found the following:

<q 
cite="http://www.w3.org/TR/CSS21/visuren.html#display-prop">

none 
   This value causes an element to generate no boxes in the 
   formatting structure (i.e., the element has no effect on 
   layout). Descendant elements do not generate any boxes 
   either; this behavior cannot be overridden by setting 
   the 'display' property on the descendants. 

   Please note that a display of 'none' does not create an 
   invisible box; it creates no box at all. CSS includes 
   mechanisms that enable an element to generate boxes in 
   the formatting structure that affect formatting but are 
   not visible themselves. Please consult the section on 
   visibility for details. 
</q>

Which can be read as: "when the display property's value is none, it is 
not included in the formatting structure (that is, layout), but should 
still be available as a kind of generated content, which occupies no part 
of the visual canvas, but which is rendered in the aural canvas."

Other than in the definition of the display property, this reviewer 
couldn't find another instance in the draft that indicates that it 
applies 
to all media types.

It is, therefore, the Protocols & Formats working group's request that 
such verbiage be explicitly added to the CSS2.1 Technical Recommendation 
wherever and whenever appropriate, so as to remove any ambiguity as to 
the default media type when no media type is defined.
Received on Tuesday, 18 December 2007 03:25:45 GMT

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