Namespaces in XML rules and definitions:
Elements and attributes that are in namespaces are called qualified
All unprefixed attributes are unqualified
All prefixed elements are qualified
Unprefixed elements may or may not be qualified. They are qualified if they are in a default namespace.
Each schema has a target namespace
Each schema can define elements in attributes in its target namespace
A schema can also define unqualified attributes of elements in its target namespace.
A schema can also define unqualified child elements of elements in its target namespace. Unqualified child elements are called local elements. This is a very bad idea!
A schema may not define elements and attributes in namespaces other than the target namespace; i.e., for each namespace there must be at least one schema
Schemas can reference global elements and attributes defined in other schemas
by importing the schema with xsd:import and
referencing the global elements and attributes defined therein.