DNS/RFC/6761について、ここに記述してください。


Special-Use Domain Names
https://tools.ietf.org/html/rfc6761

This document specifies under what circumstances special treatment is
   appropriate, and in what ways.


6.2.  Domain Name Reservation Considerations for "test."

6.3.  Domain Name Reservation Considerations for "localhost."

6.4.  Domain Name Reservation Considerations for "invalid."

6.5.  Domain Name Reservation Considerations for Example Domains
{{{
   1.  Users SHOULD understand that example names are reserved for use in documentation.

   2.  Application software SHOULD NOT recognize example names as
       special and SHOULD use example names as they would other domain names.


   7.  DNS Registries/Registrars MUST NOT grant requests to register
       example names in the normal way to any person or entity.  All
       example names are registered in perpetuity to IANA:

}}}