It is unclear from the scope
<http://www.w3.org/TR/2005/WD-CDR-20051219/#scope> (section 1.1) that this
document is about one document referencing another and not about documents
using mixed namespace declarations. Section 1.3 makes this even more
vague. Please revise section 1.1 and 1.3 such that it is clear what the
document is about and what problems it tries to solve.