What does an XML namespace URI point to?
An XML namespace URI is simply an identifier. It is not guaranteed to point to anything and, in general, it is a bad idea to assume that it does. This point causes a lot of confusion, so we’ll repeat it here: XML NAMESPACE URIs ARE JUST IDENTIFIERS. THEY ARE NOT GUARANTEED TO POINT TO ANYTHING. An early version of the W3C’s XML Schemas used XML namespace URIs to point to an XML Schema document containing the definitions of the element types and attributes named in the namespace. However, this proved very controversial and the idea has been withdrawn.
