from
The Free On-line Dictionary of Computing (8 July 2008)
RFC 1123
<networking, standard> The {RFC} "Requirements for Internet
Hosts Application and Support" which clarifies or changes the
specification of protocols given in earlier RFCs.
RFC 1123 defines the terms "MUST", "SHOULD", "MAY",
"unconditionally compliant", "conditionally compliant".
Capitals are used to emphasise that the official definition of
the word is being used.
MUST or REQUIRED means an absolute requirement for
conformance.
SHOULD or RECOMMENDED means the item can be ignored under
certain circumstances, although the full implications should
be understood.
MAY or OPTIONAL means the implementor can choose, usually
depending on whether it is needed or not.
Something "unconditionally compliant" meets all the MUST and
SHOULD requirements, "conditionally compliant" meets all the
MUST requirements and "not compliant" - does not meet some
MUST requirement.
For example, RFC 1123 amends RFC952 to say software MUST
handle either a letter or a digit as the first character of a
{hostname}.
{(rfc:1123)}.
(1996-01-13)