def _additionalRecords(self, answer, authority, ttl):
        """
        Find locally known information that could be useful to the consumer of
        the response and construct appropriate records to include in the
        I{additional} section of that response.

        Essentially, implement RFC 1034 section 4.3.2 step 6.

        @param answer: A L{list} of the records which will be included in the
            I{answer} section of the response.

        @param authority: A L{list} of the records which will be included in
            the I{authority} section of the response.

        @param ttl: The default TTL for records for which this is not otherwise
            specified.

        @return: A generator of L{dns.RRHeader} instances for inclusion in the
            I{additional} section.  These instances represent extra information
            about the records in C{answer} and C{authority}.
        """
        for record in answer + authority:
            if record.type in self._ADDITIONAL_PROCESSING_TYPES:
                name = record.payload.name.name
                for rec in self.records.get(name.lower(), ()):
                    if rec.TYPE in self._ADDRESS_TYPES:
                        yield dns.RRHeader(
                            name, rec.TYPE, dns.IN,
                            rec.ttl or ttl, rec, auth=True)

        Find locally known information that could be useful to the consumer of
        the response and construct appropriate records to include in the
        I{additional} section of that response.

        Essentially, implement RFC 1034 section 4.3.2 step 6.

        @param answer: A L{list} of the records which will be included in the
            I{answer} section of the response.

        @param authority: A L{list} of the records which will be included in
            the I{authority} section of the response.

        @param ttl: The default TTL for records for which this is not otherwise
            specified.

        @return: A generator of L{dns.RRHeader} instances for inclusion in the
            I{additional} section.  These instances represent extra information
            about the records in C{answer} and C{authority}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/authority.py