Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words
RFC 8174

Document Type RFC - Best Current Practice (May 2017; Errata)
Updates RFC 2119
Last updated 2017-05-19
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IESG IESG state RFC 8174 (Best Current Practice)
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Internet Engineering Task Force (IETF)                          B. Leiba
Request for Comments: 8174                           Huawei Technologies
BCP: 14                                                         May 2017
Updates: 2119
Category: Best Current Practice
ISSN: 2070-1721

       Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words

Abstract

   RFC 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 in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8174.

Leiba                     Best Current Practice                 [Page 1]
RFC 8174                 RFC 2119 Clarification                 May 2017

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Clarifying Capitalization of Key Words  . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   RFC 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 updates RFC 2119 by clarifying that only UPPERCASE
   usage of the key words have the defined special meanings.  This
   document is part of BCP 14.

Leiba                     Best Current Practice                 [Page 2]
RFC 8174                 RFC 2119 Clarification                 May 2017

2.  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 in RFC 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
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