def skip(self, attr):
        """
        Get whether to skip (filter-out) the specified attribute.
        @param attr: An attribute.
        @type attr: I{Attribute}
        @return: True if should be skipped.
        @rtype: bool
        """
        ns = attr.namespace()
        skip = (
            Namespace.xmlns[1],
            'http://schemas.xmlsoap.org/soap/encoding/',
            'http://schemas.xmlsoap.org/soap/envelope/',
            'http://www.w3.org/2003/05/soap-envelope',
        )
        return ( Namespace.xs(ns) or ns[1] in skip )