Add a subtype segment

        Args:
            subtype (str): May be one of ``['a', 'c', 'r']``. See the
                `Reference Definition <https://elections.democracyclub.org.uk/reference_definition>`_.
                for valid election type/subtype combinations.

        Returns:
            IdBuilder

        Raises:
            ValueError

def with_subtype(self, subtype):
        """Add a subtype segment

        Args:
            subtype (str): May be one of ``['a', 'c', 'r']``. See the
                `Reference Definition <https://elections.democracyclub.org.uk/reference_definition>`_.
                for valid election type/subtype combinations.

        Returns:
            IdBuilder

        Raises:
            ValueError
        """
        self._validate_subtype(subtype)
        self.subtype = subtype
        return self