def _add_rr(self, name, ttl, rd, deleting=None, section=None):
        """Add a single RR to the update section."""

        if section is None:
            section = self.authority
        covers = rd.covers()
        rrset = self.find_rrset(section, name, self.zone_rdclass, rd.rdtype,
                                covers, deleting, True, True)
        rrset.add(rd, ttl)
Add a single RR to the update section.