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standards terminology non-normative terminology Specifications in RFCs contain normative keywords, as defined in RFC 2119, to signify requirements, permission or prohibitions. These include MUST, SHOULD and MAY, which are commonly recorded in all CAPITALS (but need not be). The words are sometimes also intended with non-normative meaning; this different usage can be confusing. Happily there are adequate alternatives for non-normative meanings. For such situations, this document provides some alternatives to the normative vocabulary of RFC 2119.

To indicate a degree of requirement, permission or prohibition for an aspect of a specification, words such as MUST, SHOULD and MAY are defined as normative vocabulary in the formal aspects of the RFC series.. However it is also natural to use them non-normatively, in a narrative fashion. Even when this is permitted, such as RFCs that do not invoke the conventions of RFC 2119, non-normative use of these words is often confusing; their normative meaning is too deeply ingrained in the culture of the RFC series. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in . Fortunately, there are other words readily available, in lieu of the RFC 2119 words. These alternatives, or their equivalents, SHOULD be used instead of their normatively-encumbered vocabulary. The words "needs to" and "necessary" SHOULD be used to connote that something is essential. The words "ought", "encouraged" and "suggest strongly" SHOULD be used to connote that something is strongly urged. The words "can" and "might" SHOULD be used to indicate the possibility or capability of performing an action. The words "is allowed to" or "is permitted to" SHOULD be used to indicate permission to perform an action. The word "not" can be freely used with any of the above suggestions and will not be taken to have any separate RFC 2119 connotation. The word only takes on a special meaning when it is combined with one of the RFC 2119 normative words. For example, "ought not" is non-normative, while "should not" and "SHOULD NOT" are normative in the RFC 2119 sense. RFCs that cite RFC2119 vocabulary usage MUST NOT employ the listed, normative vocabulary for non-normative meaning. RFCs that do not cite RFC2119 SHOULD NOT employ that vocabulary. Note that the above list of synonyms is not meant to be exhaustive; other non-RFC2119-normative words MAY also be used at the author's discretion. Authors who follow these guidelines MAY incorporate a declaration at the beginning of their document, but note that this is not required. This document can be discussed on the ietf@ietf.org mailing list.

Ran Atkinson

This document has no IANA considerations.

The 2119 terms are frequently used to specify behavior with security implications. The effects on security of changing something from a "MUST" to a "needs to", or vice versa, can be very subtle, as one has normative meaning and the other does not. Document authors need to take the time to consider the effects of using non-normative verbiage as specified in this document instead of the normative verbiage from 2119.

&RFC2119;