public boolean
isIXFR() {
	return (rtype == Type.IXFR);
}
Returns true if the response is an IXFR-style response (List of Deltas).
This will be true only if an IXFR was performed and the server provided
an incremental zone transfer.
src/main/java/core/org/xbill/DNS/ZoneTransferIn.java