Overview#
RFC 2119 is a
RFC describing Key words for use in
RFCs to Indicate Requirement Levels
We refer you to the full text
.
RFC 8174 updates RFC 2119 by clarifying that only
UPPERCASE usage of the key words have the
defined special meanings.
RFC 8174 document is part of
BCP 14.
RFC 2119 includes: (Terms on the same line imply the same meaning)
Guidance in the use of these Imperatives#
Imperatives of the type defined in this memo
MUST be used with care and sparingly. In particular, they
MUST only be used where it is actually required for interoperation or to limit behavior which has potential for causing harm (e.g., limiting retransmissions) For
example, they
MUST NOT be used to try to impose a particular method on implementers where the method is not required for interoperability.
These terms are frequently used to specify behavior with security implications. The effects on security of not implementing a
MUST or
SHOULD, or doing something the specification says
MUST NOT or
SHOULD NOT be done may be very subtle. Document authors should take the time to elaborate the
security implications of not following recommendations or requirements as most implementers will not have had the benefit of the experience and discussion that produced the specification.
There might be more information for this subject on one of the following:
