The purpose of this is to provide a diagnostic tool to see if a given
nameserver and/or zone has been set up in a consistent fashion.
Providing only a zone requests a check on the zone as it is currently listed in the DNS. Providing only a nameserver or nameservers requests a basic check on whether a nameserver process is running on the supplied nameserver(s).
Providing both a zone and (a) nameserver(s) requests the full suite of checks to be performed on both the nameserver(s), and the zone as served by those nameserver(s).