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Re: Minutes for July 30th, 2009 RDFa Telecon

From: Philip Taylor <pjt47@cam.ac.uk>
Date: Wed, 05 Aug 2009 15:11:59 +0100
Message-ID: <4A79932F.2050905@cam.ac.uk>
To: martin@weborganics.co.uk
CC: Manu Sporny <msporny@digitalbazaar.com>, RDFa Developers <public-rdf-in-xhtml-tf@w3.org>
Martin McEvoy wrote:
> 
> ...
> 
> Is there anything wrong with using xmlns: in the way I have proposed 
> above?  as I am unsure of what the Issues may be?, I think structure an 
> content are more clearly defined....? also xmlns is not depreciated in 
> html5 so really what's the cost?

HTML 5 (in its text/html serialisation) currently doesn't allow xmlns: 
to be used in that way. The only thing it allows is 
xmlns="http://www.w3.org/1999/xhtml" on an HTML element, and a few 
special cases in inline MathML/SVG content. Anything else is invalid.

It's unlikely that HTML 5 would allow xmlns: (or any other attribute 
name containing a colon) in valid documents, because it would either 
encourage violation of the "DOM Consistency" principle 
(http://www.w3.org/TR/html-design-principles/) or would risk violating 
"Support Existing Content".

(Web browsers parse xmlns:prefix="..." in text/html as an attribute with 
local name "xmlns:prefix" in no namespace, whereas XML parsers give it 
local name "prefix" in the XMLNS namespace, hence the DOM inconsistency 
(which affects namespace-aware DOM APIs, CSS selectors, etc), so people 
should be discouraged from using syntax with unexpected behaviour like 
that, to avoid making the language more confusing than it already is; 
and changing text/html parsers to be consistent with XML would break 
some current pages that rely on the current behaviour.)

-- 
Philip Taylor
pjt47@cam.ac.uk
Received on Wednesday, 5 August 2009 14:12:35 GMT

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