Yes, as long as they don't use the same prefixes and at most one of
them is the default XML namespace. For example, in the following, the
http://www.google.org/ and http://www.bar.org/ namespaces are both in
scope for all elements:
One consequence of this is that you can place all XML namespace
declarations on the root element and they will be in scope for all
elements. This is the simplest way to use XML namespaces.