Hi Bill,
I would start by quoting some text from XMP Spec Part 1 section 8.1 Core Properties - Overview
“This document does not claim ownership over those namespaces. Their
respective owners may define additional XMP names in those namespaces, whether properties, structure
fields, or qualifiers.
NOTE Unless local conditions dictate otherwise, XMP processors are encouraged to support the unrestricted use of XMP
properties in these and other namespaces. There is no intent that the properties defined here be the only allowed ones.”
Therefore, XMP Toolkit SDK doesn’t validate the namespace properties in a XMP, defined even in the Specifications, against some schema.
I hope this answers your question – as the support for the http://www.w3.org/2001/XMLSchema-instance schema is not needed by design.
Thanks
Inder