code: public static ZoneTransferIn
  newIXFR(Name zone, long serial, boolean fallback, SocketAddress address,
  	TSIG key)
  {
  	return new ZoneTransferIn(zone, Type.IXFR, serial, fallback, address,
  				  key);
  }
docs: Instantiates a ZoneTransferIn object to do an IXFR (incremental zone
  transfer).
  @param zone The zone to transfer.
  @param serial The existing serial number.
  @param fallback If true, fall back to AXFR if IXFR is not supported.
  @param address The host/port from which to transfer the zone.
  @param key The TSIG key used to authenticate the transfer, or null.
  @return The ZoneTransferIn object.