: the HTTP method for the rule if there are different
                       URLs for different methods on the same endpoint.
        :param force_external: enforce full canonical external URLs. If the URL
                               scheme is not provided, this will generate
                               a protocol-relative URL.
        :param append_unknown: unknown parameters are appended to the generated
                               URL as query string argument.  Disable this
                               if you want the builder to ignore those.
        :param url_scheme: Scheme to use in place of the bound
            :attr:`url_scheme`.

        .. versionchanged:: 2.0
            Added the ``url_scheme`` parameter.

        .. versionadded:: 0.6
           Added the ``append_unknown`` parameter.
        c