资料来源 : Free On-Line Dictionary of Computing

RFC 1123
     
         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)