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   RE: [xml-dev] Problems with xs:redefine

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> I would think, however, that you could *directly 
> substitute the
> elements contained in the group, for the group element 
> itself* (since that's
> what comes out in the XML instance), in the redefined element 
> definition
> instead. Saxon-SA allows this, but Xerces complains that the 
> element is then
> not a valid restriction of the content model of the base. 
> Any idea what the correct interpretation of the spec is? 

The spec states an intent (to paraphrase: A is a valid restriction of B if
and only if the set of valid instances of A is a subset of the set of valid
instances of B) and then gives an algorithm which doesn't have the desired
property. The general view is that the algorithm is normative even though it
is known to be incorrect. Saxon implements an improved algorithm published
by Henry Thompson and Richard Tobin in 2003; although this algorithm is
closer to the stated intent of the spec, it's non-conformant.

Michael Kay


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