Question on namespaces and DTDs

Hi

I have a question about DTDs and "Namespaces in XML".

First of all, is it true that any well-formed XML document according to
"Namespaces in XML" must be well-formed according to XML 1.0 in the
first place?   Is it true that "Namespaces in XML" is - syntactically -
a subset of XML 1.0? 

If the answer is yes, suppose that a document contains an element whose
QName is  "abc:el".  If the document contains a DTD, how should this
element type be declared?   As "abc:el", I guess.  What if the document
also contains another element  "xyz:el"  and the "xyz" prefix is bound
to the same namespace name as "abc"?  I guess that, at the DTD level,
"abc:el" and "xyz:el" are two distinct element types and both must be
declared independently.  

Are my conclusions right?

Alessandro Triglia