Major http://docs.oasis-open.org/specGuidelines/ndr/namingDirectives-v1.3.html#xml-namespaces requires that:
TCs must define a namespace versioning policy for any XML namespace declared in a specification, and must communicate the text expressing such policy to the TC Administrator for incorporation into the appropriate namespace document.
The requirement refers to http://www.w3.org/TR/webarch/#versioning-xmlns.