def bind(cls, ns, location=None):
        """
        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
        """
        if location is None:
            location = ns
        cls.locations[ns] = location