[1] RFC 2606 - Reserved Top Level DNS Names, 2021-03-28T07:19:55.000Z, 2021-04-09T08:41:39.119Z https://tools.ietf.org/html/rfc2606#section-2

[2] RFC 6761 - Special-Use Domain Names ( (2013-06-27 22:35:13 +09:00 版)) http://tools.ietf.org/html/rfc6761#section-6.5