def _multi_parameter(args):
            """
            According to the spec::

                If more than one capability is named, the RFC1459 designated
                sentinel (:) for a multi-parameter argument must be present.

            It's not obvious where the sentinel should be present or if it
            must be omitted for a single parameter, so follow convention and
            only include the sentinel prefixed to the first parameter if more
            than one parameter is present.
            """
            if len(args) > 1:
                return (':' + args[0],) + args[1:]
            return args