code: def _register_client_authenticator(klass, name):
      
      # pylint: disable-msg=W0212
      CLIENT_MECHANISMS_D[name] = klass
      items = sorted(CLIENT_MECHANISMS_D.items(), key = _key_func, reverse = True)
      CLIENT_MECHANISMS[:] = [k for (k, v) in items ]
      SECURE_CLIENT_MECHANISMS[:] = [k for (k, v) in items
                                                      if v._pyxmpp_sasl_secure]
docs: Add a client authenticator class to `CLIENT_MECHANISMS_D`,
      `CLIENT_MECHANISMS` and, optionally, to `SECURE_CLIENT_MECHANISMS`