3.4.1. Prescan

3.4.1.1. The Update Section is parsed into RRs and each RR's CLASS is checked to see if it is ANY, NONE, or the same as the Zone Class, else signal a FORMERR to the requestor. Using the definitions in Section 1.2, each RR's NAME must be in the zone specified by the Zone Section, else signal NOTZONE to the requestor.

3.4.1.2. For RRs whose CLASS is not ANY, check the TYPE and if it is ANY, AXFR, MAILA, MAILB, or any other QUERY metatype, or any unrecognized type, then signal FORMERR to the requestor. For RRs whose CLASS is ANY or NONE, check the TTL to see that it is zero (0), else signal a FORMERR to the requestor. For any RR whose CLASS is ANY, check the RDLENGTH to make sure that it is zero (0) (that is, the RDATA field is empty), and that the TYPE is not AXFR, MAILA, MAILB, or any other QUERY metatype besides ANY, or any unrecognized type, else signal FORMERR to the requestor.

3.4.1.3. Pseudocode For Update Section Prescan

      [rr] for rr in updates
           if (zone_of(rr.name) != ZNAME)
                return (NOTZONE);
           if (rr.class == zclass)
                if (rr.type & ANY|AXFR|MAILA|MAILB)
                     return (FORMERR)
           elsif (rr.class == ANY)
                if (rr.ttl != 0 || rr.rdlength != 0
                    || rr.type & AXFR|MAILA|MAILB)
                     return (FORMERR)
           elsif (rr.class == NONE)
                if (rr.ttl != 0 || rr.type & ANY|AXFR|MAILA|MAILB)
                     return (FORMERR)
           else
                return (FORMERR)