code: public static ResourceRecordSet<PTRData> ptr(String name, String ptrdname) {
      return new PTRBuilder().name(name).add(ptrdname).build();
    }
docs: creates ptr set of ptr single {@link denominator.model.rdata.PTRData PTR} record for the
  specified name.
  
  @param name     ex. {@code denominator.io.}
  @param ptrdname ex. {@code ptr1.denominator.io.}