docs: def check_valid_locations(self, locations=None):
          """Fail if 'locations' contains bad destinations.
          """
          if locations is None:
              locations = self.locations
          for location in locations:
              if (not self.is_server(location) and
                  not self.is_ssh_url(location) and
                  not self.has_host(location)):
                  err_exit('Unknown location: %(location)s' % locals())