6. Addresses used in examples SHOULD use fully qualified domain names
instead of literal IP addresses, and SHOULD use example fqdn's
such as foo.example.com instead of real-world fqdn's. See
[RFC2606] (Eastlake, D. and A. Panitz, "Reserved Top Level DNS
Names," June 1999.) for example domain names that can be used.
Why the SHOULD? Presumably, because you don't want naive folk to take
the examples in the RFC and use them in local config files and such,
causing problems or other undesirable effects when they (unexpectedly)
get used in the real world..
But in cases where this really is not a concern, there is also
presumably not a need to _require_ use of the example names.
