Schema in UTF-8 instance in UTF-16?

Hello Everybody,

I'm a member of a group developing standard XML schemas (in English), based
on which, members worldwide develop instance documents, according to their
needs. Worldwide means populating them with data in various languages,
scripts etc. For some languages the more suitable choice of encoding would
be UTF-16, but our in schemas we use UTF-8. Recently we are struggling with
the following question: would it be possible to use both, i.e. a schema
encoded in UTF-8 and an instance in UTF-16? That would mean that tags are
encoded in UTF-8 and data (attribute values and element contents) in UTF-16.
Is it possible to parse such a document? Is there any mechanism to
facilitate that or to 'switch' between UTF sets at the XML level?

I would appreciate any suggestions or references

Thank you

Ewa Iwicka