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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Hansen 3 Internet-Draft AT&T Laboratories 4 Intended status: Informational D. Crocker 5 Expires: December 25, 2015 Brandenburg InternetWorking 6 June 23, 2015 8 Non-Normative Synonyms in RFCs 9 draft-hansen-nonkeywords-non2119-03 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 December 25, 2015. 43 Copyright Notice 45 Copyright (c) 2015 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 is 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 to be interpreted as described in [RFC2119]. 74 Fortunately, there are other words readily available, in lieu of the 75 RFC 2119 words, when a non-normative meaning is intended. These 76 alternatives, or their equivalents, are suggested for use instead of 77 their normatively-encumbered vocabulary. 79 +-------------+----------------------------------+------------------+ 80 | RFC 2119 | When Used With This Meaning | Alternative | 81 | Word | | Word(s) | 82 +-------------+----------------------------------+------------------+ 83 | MUST, | indicates that something is | needs to, | 84 | REQUIRED, | essential | necessary | 85 | SHALL | | | 86 | | | | 87 | SHOULD, | indicates that something is | ought to, | 88 | RECOMMENDED | strongly urged | encouraged, | 89 | | | suggested | 90 | | | | 91 | MAY, | indicates the possibility or | can, might | 92 | OPTIONAL | capability of performing an | | 93 | | action | | 94 | | | | 95 | | indicates permission to perform | is allowed to, | 96 | | an action | is permitted to | 97 +-------------+----------------------------------+------------------+ 99 Because the word "NOT" (or "not") only takes on a special meaning 100 when it is combined with one of the RFC 2119 normative words, the 101 word "not" can be freely used with any of the above suggestions and 102 will not be taken to have any separate RFC 2119 connotation. For 103 example, "ought not" is non-normative, while "should not" and "SHOULD 104 NOT" are normative in the RFC 2119 sense. 106 As a rule, authors are strongly encouraged to use these alternative 107 wordings, or their equivalents, in ALL documents processed as RFCs, 108 but especially for those that conform to RFC 2119. (Of course, these 109 words might also be used in internet drafts.) 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 has normative meaning and the other does not. Document authors 136 need to take the time to consider the effects of using non-normative 137 verbiage as specified in this document instead of the normative 138 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, March 1997. 145 Authors' Addresses 147 Tony Hansen 148 AT&T Laboratories 149 200 Laurel Ave South 150 Middletown, NJ 07748 151 USA 153 Phone: +1.732.420.8934 154 Email: tony+nonkeywords@maillennium.att.com 156 D. Crocker 157 Brandenburg InternetWorking 158 675 Spruce Dr. 159 Sunnyvale 160 USA 162 Phone: +1.408.246.8253 163 Email: dcrocker@bbiw.net 164 URI: http://bbiw.net