code: public static ResourceRecordSet<PTRData> ptr(String name, Collection<String> ptrdnames) {
      return new PTRBuilder().name(name).addAll(ptrdnames).build();
    }
docs: creates ptr set of {@link denominator.model.rdata.PTRData PTR} records for the specified name.
  
  @param name      ex. {@code denominator.io.}
  @param ptrdnames ptrdname values ex. {@code [ptr1.denominator.io., ptr2.denominator.io.]}