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Network Working Group                                          T. Hansen
Internet-Draft                                         AT&T Laboratories
Intended status: Informational                                D. Crocker
Expires: December 25, 2015                   Brandenburg InternetWorking
                                                           June 23, 2015


                     Non-Normative Synonyms in RFCs
                  draft-hansen-nonkeywords-non2119-03

Abstract

   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 RFC 2119 words are sometimes also
   used with non-normative meaning; this non-normative usage can be
   confusing and it is better to restrict the RFC 2119 words to be used
   solely as normative directives.

   Happily, natural languages permit variation in phrasing, so that
   meaning can be retained without use of this otherwise-normative
   vocabulary.  For such situations, this document provides some
   alternatives to the normative vocabulary of RFC 2119.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 25, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

1.  Words That Do Double Duty

   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 [RFC2119].  However it is also natural to use them non-
   normatively, in a narrative fashion.  Even when this is carries no
   obvious potential confusion, such as within RFCs that do not invoke
   the conventions of RFC 2119, non-normative use of these words in RFCs
   invites confusion for the reader; 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 [RFC2119].

   Fortunately, there are other words readily available, in lieu of the
   RFC 2119 words, when a non-normative meaning is intended.  These
   alternatives, or their equivalents, are suggested for use instead of
   their normatively-encumbered vocabulary.





















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   +-------------+----------------------------------+------------------+
   | RFC 2119    | When Used With This Meaning      | Alternative      |
   | Word        |                                  | Word(s)          |
   +-------------+----------------------------------+------------------+
   | MUST,       | indicates that something is      | needs to,        |
   | REQUIRED,   | essential                        | necessary        |
   | SHALL       |                                  |                  |
   |             |                                  |                  |
   | SHOULD,     | indicates that something is      | ought to,        |
   | RECOMMENDED | strongly urged                   | encouraged,      |
   |             |                                  | suggested        |
   |             |                                  |                  |
   | MAY,        | indicates the possibility or     | can, might       |
   | OPTIONAL    | capability of performing an      |                  |
   |             | action                           |                  |
   |             |                                  |                  |
   |             | indicates permission to perform  | is allowed to,   |
   |             | an action                        | is permitted to  |
   +-------------+----------------------------------+------------------+

   Because the word "NOT" (or "not") only takes on a special meaning
   when it is combined with one of the RFC 2119 normative words, 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.  For
   example, "ought not" is non-normative, while "should not" and "SHOULD
   NOT" are normative in the RFC 2119 sense.

   As a rule, authors are strongly encouraged to use these alternative
   wordings, or their equivalents, in ALL documents processed as RFCs,
   but especially for those that conform to RFC 2119.  (Of course, these
   words might also be used in internet drafts.)

   Note that the above list of synonyms is not meant to be exhaustive;
   other non-RFC-2119-normative words can, of course, also be used at
   the author's discretion.

   Authors who follow these guidelines might want to incorporate a
   declaration about usage, at the beginning of their document.

   [Note to RFC Editor: please remove this paragraph before
   publication.]  This document can be discussed on the ietf@ietf.org
   mailing list.

2.  Acknowledgements

   The comments from Ran Atkinson are gratefully acknowledged.





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3.  IANA Considerations

   This document has no IANA considerations.

4.  Security Considerations

   The RFC 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 RFC 2119.

5.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

Authors' Addresses

   Tony Hansen
   AT&T Laboratories
   200 Laurel Ave South
   Middletown, NJ  07748
   USA

   Phone: +1.732.420.8934
   Email: tony+nonkeywords@maillennium.att.com


   D. Crocker
   Brandenburg InternetWorking
   675 Spruce Dr.
   Sunnyvale
   USA

   Phone: +1.408.246.8253
   Email: dcrocker@bbiw.net
   URI:   http://bbiw.net











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