Dear all, According to your suggestions and thinkings including mine, I updated the IPTR document. In short, ONLY ONE ACE domain name is enough for the PTR RR, though maybe there are a lot iDNs in UTF-8 stored in IPTR RRs. I hope I explain them clearly. Strictly speaking, a set of canonical IDNs. In short, in every single language, it is possible that more than ONE domain name exist for the same host.
Any comment is welcome.