def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def _verify_toplevel_json(self, replay_data):
        fn = self._filename

        if "version" not in replay_data:
            raise TransactionReplayError(fn, _('Missing key "{key}".'.format(key="version")))

        self._assert_type(replay_data["version"], str, "version", "string")

        _check_version(replay_data["version"], fn)