dns.rdataset.DifferingCovers:
An attempt was made to add a DNS SIG/RRSIG whose covered type is
not the same as that of the other rdatas in the rdataset.
dns.rdtypes.mxbase.UncompressedMX:
Base class for rdata that is like an MX record, but whose name is
not compressed when converted to DNS wire format, and whose
digestable form is not downcased.
dns.rdtypes.nsbase.UncompressedNS:
Base class for rdata that is like an NS record, but whose name is
not compressed when convert to DNS wire format, and whose
digestable form is not downcased.