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Re: What's the problem? "Reuse of 1998 XHTML namespace is potentially misleading/wrong"

From: Maciej Stachowiak <mjs@apple.com>
Date: Thu, 12 Feb 2009 16:18:38 -0800
Cc: Lachlan Hunt <lachlan.hunt@lachy.id.au>, HTML WG <public-html@w3.org>
Message-id: <152C8694-7537-458B-BC56-002D39210493@apple.com>
To: Larry Masinter <masinter@adobe.com>


On Feb 11, 2009, at 12:46 PM, Larry Masinter wrote:

>>
>> But XHTML2 also has several major incompatibilities with XHTML1,  
>> which
>> would effectively make it impossible to implement both XHTML 1.x  
>> and 2
>> in the same implementation, if they share the same namespace [3].
>
> The fact that one language makes <title>abc</title> equivalent
> to <meta property="title" content="Document Title"/> and the other
> does not does mean the languages are incompatible. But the elements
> "title" and "meta" have the same meaning as vocabulary items, their
> usage is different in the two languages.
>
> I know that there is significant resistance to the idea that you might
> define a vocabulary independent of a language which uses that  
> vocabulary,
> or that you might define a language independent of the processing  
> rules
> by which instances of text in the language should be processed, but
> those separations are fundamental to the design of XML, and the  
> question
> here is about XML namespaces and their use.

What Lachlan raises is an actual technical problem in the design of  
the languages, even if the languages have "the same vocabulary" in  
some sense. It is not possible to implement a user agent that conforms  
to both XHTML5 and XHTML2. In many cases the same elements or  
attributes are defined to have different processing requirements.  
Since DTDs are optional, and since elements in the XHTML namespace may  
appear in a compound document, there is no way to determine which  
processing requirements to use. XHTML2 also has this problem with  
regard to XHTML1.x.

I don't believe any vendor currently plans to support XHTML5 and  
XHTML2 together in the same product, so perhaps this is not a problem  
in practice. But it is still a design flaw in XHTML2 and should be  
fixed by the XHTML2 Working Group.

Regards,
Maciej
Received on Friday, 13 February 2009 00:19:19 UTC

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