-*- outline -*-

* What characters may be used for host name?

As say RFC 952 hostname is a text string up to 24 characters drawn from the alphabet
(A-Z), digits (0-9), minus sign (-), and period (.).

As say RFC 1035:

  <domain> ::= <subdomain> | " "

  <subdomain> ::= <label> | <subdomain> "." <label>

  <label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]

  <ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str>

  <let-dig-hyp> ::= <let-dig> | "-"

  <let-dig> ::= <letter> | <digit>

  <letter> ::= any one of the 52 alphabetic characters A through Z in
  upper case and a through z in lower case

  <digit> ::= any one of the ten digits 0 through 9