xs:redefine and interoperability problems

Hi,

I'm not sure whether this is the right forum for my question, but here
it goes, please forward me somewhere else if this is offtopic.

Suppose the following schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="http://www.w3.org/1999/xhtml"
           xmlns="http://www.w3.org/1999/xhtml">

  <xs:redefine schemaLocation="http://www.w3.org/MarkUp/SCHEMA/xhtml11.xsd">

    <xs:group name="tr.content">
      <xs:sequence>
        <xs:choice maxOccurs="unbounded">
          <!-- Remove th: <xs:element ref="th"/> -->
          <xs:element ref="td"/>
        </xs:choice>
      </xs:sequence>
    </xs:group>

  </xs:redefine>

</xs:schema>

Xerces-J and .NET validators are complaining about circular group
references.

XSV and libxml are happy with such schema.

Saxon-SA, MSXML 4.0 and Xerces-J complain about tr.content group not
being defined in xs:redefined schema (it is in fact defined in schema
which is included into the redefined schema).

As a dedicated RELAX NG user I could smile under my beard ;-)
But anyway, I thought that WXS interoperability is better in 2007.

Is my schema correct? If no, why? If yes, will be underspecified
behaviour (which is probably cause of incompatibilities between
implementations) improved in WXS 1.1?

Thanks,

				Jirka

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