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Re: ISSUE-4: Versioning, namespace URIs and MIME types ISSUE-60

From: Ian Hickson <ian@hixie.ch>
Date: Fri, 20 Feb 2009 04:12:37 +0000 (UTC)
To: Robert J Burns <rob@robburns.com>
Cc: HTML WG <public-html@w3.org>
Message-ID: <Pine.LNX.4.62.0902200403130.6186@hixie.dreamhostps.com>
On Thu, 19 Feb 2009, Robert J Burns wrote:
> HTML5 has specified error-handling for the 'img' element. I guess it is 
> not an issue then. But you began this particular thread with an example 
> of an 'img' element which you claimed was a compatibility problem in 
> that alternate text for the image might either be expressed as the value 
> of the 'alt' attribute or in the contents of the element.

The only problem I was trying to show is that an implementation that 
implements both XHTML2 and XHTML1 in the same namespace would be faced 
with an irreconcilable difference in semantics when an element in the 
"http://www.w3.org/1999/xhtml" namespace with the tag name "img" is 
created without any other context, since the two specs have conflicting 
requirements (or rather, since XHTML2 has requirement that conflict with 
the requirements imposed by legacy content). This is merely intended to 
show that if XHTML2 does use the same namespace as XHTML1, the two 
languages cannot be sanely implemented in the same user agent.

The point being that HTML5 has no real choice regarding what namespace it 
uses, and that any compatibility issue that XHTML2 has is actually not a 
clash with XHTML5 but a clash with XHTML1. I also indicated that in my 
opinion this is not necessarily even a problem for XHTML2, since it may be 
(as indicated by XHTML2 itself in section 1.1.2) that "strict element-wise 
backwards compatibility is no longer necessary", and thus that software 
need not implement both languages at all.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Friday, 20 February 2009 04:13:16 UTC

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