Returns the namespace of the top level element providing the instance is schema-based rather than a fragment.The member function returns the namespace URI of the top level element providing that the given instance is schema-based and is well-formed. This function returns NULL if the instance is a fragment. If there are many top level elements then they may have different namespace URIs and if there is no top level element then there is nothing to return. It also returns NULL if the instance is non-schema based for compatibility.
Returns the namespace of the top level element providing the instance
is schema-based rather than a fragment.The member function returns the namespace URI of the top level element
providing that the given instance is schema-based and is well-formed.
This function returns NULL if the instance is a fragment.
If there are many top level elements then they may have different
namespace URIs and if there is no top level element then there is nothing
to return. It also returns NULL if the instance is non-schema based for compatibility.