code: def bind(cls, ns, location=None):
          
          if location is None:
              location = ns
          cls.locations[ns] = location
docs: Bind a namespace to a schema location (URI).
          This is used for imports that don't specify a schemaLocation.
          @param ns: A namespace-uri.
          @type ns: str
          @param location: The (optional) schema location for the
              namespace.  (default=ns).
          @type location: str