Non-Normative Synonyms in RFCs

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Last updated 2016-02-26
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Network Working Group                                          T. Hansen
Internet-Draft                                         AT&T Laboratories
Intended status: Informational                                D. Crocker
Expires: August 29, 2016                     Brandenburg InternetWorking
                                                       February 26, 2016

                     Non-Normative Synonyms in RFCs


   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.

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   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Hansen & Crocker         Expires August 29, 2016                [Page 1]
Internet-Draft              RFC Non-Keywords               February 2016

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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 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",
   document are meant to reference their occurrence in [RFC2119].  The
   words are not used normatively here.

   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, can be used instead of the
   normatively-encumbered vocabulary.

Hansen & Crocker         Expires August 29, 2016                [Page 2]
Internet-Draft              RFC Non-Keywords               February 2016

   | RFC 2119    | When Used With This Meaning      | Some Alternative |
   | Word        |                                  | Word(s)          |
   | MUST,       | indicates that something is      | needs to,        |
   | REQUIRED,   | essential                        | necessary        |
   | SHALL       |                                  |                  |
   |             |                                  |                  |
   | SHOULD,     | indicates that something is      | ought to,        |
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