xsd schema limitations in IntelliSense and others

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I'm enjoying the wide-range of uses of XML in the VS .Net offerings. I'm a
bit caught-offf, however, over lack of clear documentation on what is and
what is not supported. Can anyone point me to a reference doc?

The current (latest of several) little xml issues is that it seems
IntelliSense doesn't handle <xsd:include>, <xsd:import>, <xsd:redefine> nor
various interesting constructs such as extending a complex type or
specifying a substitutionGroup. Are these limitations documented anywhere?
Has anyone had luck using any of these with Intellisense?

(There's a similar issue with DataSets and .xsd, but it seems that might be
more due to the default nested format that MS uses for its datasets. And
there's an OK work-around writing code to do dataSet.Merge()...)

Thanks,

Ezra E.