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Hansen 3 Internet-Draft AT&T Laboratories 4 Intended status: Informational D. Crocker 5 Expires: August 29, 2016 Brandenburg InternetWorking 6 February 26, 2016 8 Non-Normative Synonyms in RFCs 9 draft-hansen-nonkeywords-non2119-04 11 Abstract 13 Specifications in RFCs contain normative keywords, as defined in RFC 14 2119, to signify requirements, permission or prohibitions. These 15 include MUST, SHOULD and MAY, which are commonly recorded in all 16 CAPITALS (but need not be). The RFC 2119 words are sometimes also 17 used with non-normative meaning; this non-normative usage can be 18 confusing and it is better to restrict the RFC 2119 words to be used 19 solely as normative directives. 21 Happily, natural languages permit variation in phrasing, so that 22 meaning can be retained without use of this otherwise-normative 23 vocabulary. For such situations, this document provides some 24 alternatives to the normative vocabulary of RFC 2119. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on August 29, 2016. 43 Copyright Notice 45 Copyright (c) 2016 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 1. Words That Do Double Duty 60 To indicate a degree of requirement, permission or prohibition for an 61 aspect of a specification, words such as MUST, SHOULD and MAY are 62 defined as normative vocabulary in the formal aspects of the RFC 63 series [RFC2119]. However it is also natural to use them non- 64 normatively, in a narrative fashion. Even when this carries no 65 obvious potential confusion, such as within RFCs that do not invoke 66 the conventions of RFC 2119, non-normative use of these words in RFCs 67 invites confusion for the reader; their normative meaning is too 68 deeply ingrained in the culture of the RFC series. 70 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 71 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 72 document are meant to reference their occurrence in [RFC2119]. The 73 words are not used normatively here. 75 Fortunately, there are other words readily available, in lieu of the 76 RFC 2119 words, when a non-normative meaning is intended. These 77 alternatives, or their equivalents, can be used instead of the 78 normatively-encumbered vocabulary. 80 +-------------+----------------------------------+------------------+ 81 | RFC 2119 | When Used With This Meaning | Some Alternative | 82 | Word | | Word(s) | 83 +-------------+----------------------------------+------------------+ 84 | MUST, | indicates that something is | needs to, | 85 | REQUIRED, | essential | necessary | 86 | SHALL | | | 87 | | | | 88 | SHOULD, | indicates that something is | ought to, | 89 | RECOMMENDED | strongly urged | encouraged, | 90 | | | suggested | 91 | | | | 92 | MAY, | indicates the possibility or | can, might | 93 | OPTIONAL | capability of performing an | | 94 | | action | | 95 | | | | 96 | | indicates permission to perform | is allowed to, | 97 | | an action | is permitted to | 98 +-------------+----------------------------------+------------------+ 100 Because the word "NOT" (or "not") only takes on a special meaning 101 when it is combined with one of the RFC 2119 normative words, the 102 word "not" can be freely used with any of the above suggestions and 103 not be taken to have any separate RFC 2119 connotation. For example, 104 "ought not" is non-normative, while "should not" and "SHOULD NOT" 105 might be normative in the RFC 2119 sense. 107 By using these alternative wordings, authors of RFCs and internet 108 drafts can avoid the possibility of vocabulary (that is sometimes 109 used normatively) being misinterpreted. 111 Note that the above list of synonyms is not meant to be exhaustive; 112 other non-RFC-2119-normative words can, of course, also be used at 113 the author's discretion. 115 Authors who follow these guidelines might want to incorporate a 116 declaration about usage at the beginning of their document. 118 [Note to RFC Editor: please remove this paragraph before 119 publication.] This document can be discussed on the ietf@ietf.org 120 mailing list. 122 2. Acknowledgements 124 The comments from Ran Atkinson are gratefully acknowledged. 126 3. IANA Considerations 128 This document has no IANA considerations. 130 4. Security Considerations 132 The RFC 2119 terms are frequently used to specify behavior with 133 security implications. The effects on security of changing something 134 from a "MUST" to a "needs to", or vice versa, can be very subtle, as 135 one can have normative meaning and the other does not. Document 136 authors need to take the time to consider the effects of using non- 137 normative verbiage as specified in this document instead of the 138 normative verbiage from RFC 2119. 140 5. Informative References 142 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 143 Requirement Levels", BCP 14, RFC 2119, 144 DOI 10.17487/RFC2119, March 1997, 145 . 147 Authors' Addresses 149 Tony Hansen 150 AT&T Laboratories 151 200 Laurel Ave South 152 Middletown, NJ 07748 153 USA 155 Phone: +1.732.420.8934 156 Email: tony@att.com 158 D. Crocker 159 Brandenburg InternetWorking 160 675 Spruce Dr. 161 Sunnyvale 162 USA 164 Phone: +1.408.246.8253 165 Email: dcrocker@bbiw.net 166 URI: http://bbiw.net