[2] 
>IDNA does not apply to domain names in the NAME and RDATA fields of
DNS resource records whose CLASS is not IN.  This exclusion applies
to every non-IN class, present and future, except where future
standards override this exclusion by explicitly inviting the use of IDNA.

;; [1] [CITE@en[RFC 3490 - Internationalizing Domain Names in Applications (IDNA)]] ([TIME[2011-01-08 12:07:35 +09:00]] 版) <http://tools.ietf.org/html/rfc3490#section-3.2.1>

;; [3] [CITE@en[RFC 5891 - Internationalized Domain Names in Applications (IDNA): Protocol]] ([TIME[2011-02-05 07:34:21 +09:00]] 版) <http://tools.ietf.org/html/rfc5891#section-3.2.1>