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Namespace declarations for 'xml' and 'xmlns'

From: Jeni Tennison <jeni@jenitennison.com>
Date: Wed, 23 Sep 2009 14:42:07 +0100
Message-Id: <C12DF347-0D9B-46EA-A826-1BD83746D6B9@jenitennison.com>
To: "public-rdf-in-xhtml-tf.w3.org list" <public-rdf-in-xhtml-tf@w3.org>

One thing that Philip's tests highlight is the special handling of the  
'xml' and 'xmlns' prefixes.

In XML, the 'xml' and 'xmlns' prefixes are implicitly bound, such that  
every element effectively has a namespace declaration binding 'xml' to  
the XML namespace and 'xmlns' to the XMLNS namespace. It is illegal to  
define the XMLNS namespace or to bind the XML namespace to any prefix  
other than 'xml'.

In RDFa, the set of namespace mappings is initialised to empty, and  
are "created by authors via the XML namespace syntax".

My questions are:

1. Does the use of the XML namespace syntax within RDFa include the  
constraints on the bindings of the 'xmlns' and 'xml' prefixes?

   (a) is an xmlns:xmlns="..." attribute invalid (and hence ignored)?
   (b) is an xmlns:xml="http://example.org/" attribute invalid (and  
hence ignored)?

2. Is it intended that the namespace bindings seen by RDFa processors  
is different from those seen by standard XML processors (due to the  
lack of implicit bindings for the XML and XMLNS namespaces)?

Thanks in advance for clarifications.

Jeni Tennison
Received on Wednesday, 23 September 2009 13:42:48 UTC

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