ACTION-982: style sheets

ACTION-982

Propose some specific text ref ISSUE-298 (style sheets).

The fundamental idea is to avoid irrelevant transformations of resources that are 
unambiguously identified as mobile-optimized. Style sheets are a case in point. I
already mentioned that there are proxy deployments that strip out style elements
(inline or external) marked as handheld without any particular justification.

I propose to add the following text in 4.2.9 after the very first bullet point:

-------
o  the content is CSS and within the scope of a @media declaration explicitly 
   associated with the handheld media type;
o  the content is an included resource explicitly associated with the handheld
   media type;
-------

The first bullet point takes care of two situations:
1.  inline and internal style rules, bracketed by @media handheld, ... { ...rules...}
2.  CSS rules contained in an external style sheet and themselves bracketed as in 1.
In both cases, the CSS in question is self-descriptively marked as mobile-specific.

The second bullet point takes care of two further situations:
2.  external style sheets referred to from an HTML/XHTML document: 
    <link rel="stylesheet" media="handheld,..." href="..." type="text/css" />
3.  external style sheets referred to from another sheet:
    @import url("...") handheld, ...;
In both cases, the referred resource is explicitly identified via a link as mobile
specific.

Given the haphazard state of CSS implementations in mobile devices, it is impossible
to rely on the first technique (@media) only; as a matter of fact, several mobile
browsers handle @media incorrectly or not at all. Describing the properties of a
resource via the link to it is the safest way and it is standards compliant. That 
this mechanism was not standardized to take into account transformation proxies
may be regrettable, but it is no justification not to try making sure that mobile
optimized sites are respected. Analysing content and then deciding to retrieve
resources depending on the media type is already considered in the guidelines in
section 4.2.7 -- and many operations of modern transcoders imply some form of session
anyway. Finally, this of course does not prevent operations such as compressing style
sheets, correcting syntax errors and the like.


E.Casais

Received on Friday, 19 June 2009 19:07:20 UTC