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Internet Engineering Task Force (IETF)                          B. LeibaRequest for Comments: 8174                           Huawei TechnologiesBCP: 14                                                         May 2017Updates:2119Category: Best Current PracticeISSN: 2070-1721Ambiguity of Uppercase vs Lowercase inRFC 2119 Key WordsAbstractRFC 2119 specifies common key words that may be used in protocol   specifications.  This document aims to reduce the ambiguity by   clarifying that only UPPERCASE usage of the key words have the   defined special meanings.Status of This Memo   This memo documents an Internet Best Current Practice.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   BCPs is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc8174.Leiba                     Best Current Practice                 [Page 1]

RFC 8174RFC 2119 Clarification                 May 2017Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Clarifying Capitalization of Key Words  . . . . . . . . . . .33.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .44.  Security Considerations . . . . . . . . . . . . . . . . . . .45.  Normative References  . . . . . . . . . . . . . . . . . . . .4   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .41.  IntroductionRFC 2119 specifies common key words, such as "MUST", "SHOULD", and   "MAY", that may be used in protocol specifications.  It says that the   key words "are often capitalized," which has caused confusion about   how to interpret non-capitalized words such as "must" and "should".   This document updatesRFC 2119 by clarifying that only UPPERCASE   usage of the key words have the defined special meanings.  This   document is part ofBCP 14.Leiba                     Best Current Practice                 [Page 2]

RFC 8174RFC 2119 Clarification                 May 20172.  Clarifying Capitalization of Key Words   The following change is made to [RFC2119]:   === OLD ===   In many standards track documents several words are used to signify   the requirements in the specification.  These words are often   capitalized.  This document defines these words as they should be   interpreted in IETF documents.  Authors who follow these guidelines   should incorporate this phrase near the beginning of their document:   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 inRFC 2119.   === NEW ===   In many IETF documents, several words, when they are in all capitals   as shown below, are used to signify the requirements in the   specification.  These capitalized words can bring significant clarity   and consistency to documents because their meanings are well defined.   This document defines how those words are interpreted in IETF   documents when the words are in all capitals.   o  These words can be used as defined here, but using them is not      required.  Specifically, normative text does not require the use      of these key words.  They are used for clarity and consistency      when that is what's wanted, but a lot of normative text does not      use them and is still normative.   o  The words have the meanings specified herein only when they are in      all capitals.   o  When these words are not capitalized, they have their normal      English meanings and are not affected by this document.   Authors who follow these guidelines should incorporate this phrase   near the beginning of their document:      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL      NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",      "MAY", and "OPTIONAL" in this document are to be interpreted as      described inBCP 14 [RFC2119] [RFC8174] when, and only when, they      appear in all capitals, as shown here.   === END ===Leiba                     Best Current Practice                 [Page 3]

RFC 8174RFC 2119 Clarification                 May 20173.  IANA Considerations   This document does not require any IANA actions.4.  Security Considerations   This document is purely procedural; there are no related security   considerations.5.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.Author's Address   Barry Leiba   Huawei Technologies   Phone: +1 646 827 0648   Email: barryleiba@computer.org   URI:http://internetmessagingtechnology.org/Leiba                     Best Current Practice                 [Page 4]