<snip>
   The
   domain name that owns a DNAME record is allowed to have other
   resource record types at that domain name, except DNAMEs, CNAMEs, or
   other types that have restrictions on what they can coexist with.
<snip>
   DNAME RRs MUST NOT appear at the same owner name as an NS RR unless
   the owner name is the zone apex; if it is not the zone apex, then the
   NS RR signifies a delegation point, and the DNAME RR must in that
   case appear below the zone cut at the zone apex of the child zone.

   If a DNAME record is present at the zone apex, there is still a need
   to have the customary SOA and NS resource records there as well.
   Such a DNAME cannot be used to mirror a zone completely, as it does
   not mirror the zone apex.

   DNAME is a singleton type, meaning only one DNAME is allowed per
   name.  The owner name of a DNAME can only have one DNAME RR, and no
   CNAME RRs can exist at that name.  These rules make sure that for a
   single domain name, only one redirection exists; thus, there's no
   confusion about which one to follow.  A server ought to refuse to
   load a zone that violates these rules.