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CTG rules: rel="stylesheet"

From: Eduardo Casais <casays@yahoo.com>
Date: Mon, 11 May 2009 04:33:32 -0700 (PDT)
Message-ID: <168869.76950.qm@web45011.mail.sp1.yahoo.com>
To: public-bpwg@w3.org

I would like to deal with an issue that had been left hanging some weeks ago: 
considering external style sheets explicitly marked as suitable for handhelds.

DESCRIPTION

It is possible to flag an external style sheet as mobile-optimized:

	<link type="text/css" rel="stylesheet" media="handheld" 
		href="http://www.thedomain.com/thestylesheet.css" />

Similarly, the CSS standard, section 7.3, defines external style sheets marked as 
"all" as "suitable for all devices":

	<link type="text/css" rel="stylesheet" media="all" 
		href="http://www.thedomain.com/thestylesheet.css" />


PROPOSAL

External style sheets explicitly marked as "handheld" or as "all" in a link element
are not to be transformed by CT-proxies. This becomes a mandatory rule in the CTG
document.


ARGUMENTS

1) From experience, it appears that some deployed CT-proxies filter out every single
external style sheet; there is no justification for this, and it should not happen.

2) media="handheld"

2.a) Referring to an external style sheet as being intended for handhelds is an 
unambiguous, conclusive indication that it does not need to be transformed to make
it compatible with mobile devices. 

2.b) As a matter of fact, the same arguments as for alternate page representations 
(link with "alternate" attribute) flagged as "handheld" apply by analogy.

3) media="all"

3.a) It appears that a number of browsers, especially newer, more powerful ones, 
ignore CSS marked as media="handheld" in favour of style sheets identified as "full 
Web". See www.alistapart.com/articles/returnofthemobilestylesheet. To cater for 
this situation, flagging an external style sheet as media="all" is appropriate, hence
CT-proxies must be prevented from interpreting media="all" as something liable to be
transformed.

3.b) Addressing the issue in 3.a) by extending media declarations thusly: 
media="handheld, all" is unsafe. In particular, there are feature phones that
cannot handle this syntax, so that no CSS gets loaded at all (some SonyEricsson for 
instance). 

3.c) Duplicating the links to external CSS is possible (i.e. one link to a style 
sheet marked as "all", another to the same style sheet marked as "handheld") is
possible. However, this forces developers to introduce redundant declarations
into their content because of an interpretation of the media attribute that is at 
odds with the CSS standard.


E.Casais


      
Received on Monday, 11 May 2009 11:34:14 UTC

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