Record
withDClass(int dclass, long ttl) {
	Record rec = cloneRecord();
	rec.dclass = dclass;
	rec.ttl = ttl;
	return rec;
}
Creates a new record identical to the current record, but with a different
class and ttl.  This is most useful for dynamic update.
src/main/java/core/org/xbill/DNS/Record.java