    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
       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 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
          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 in BCP 14 [RFC2119] [RFC8174] when, and only when, they
          appear in all capitals, as shown here.

       === END ===

    Leiba                     Best Current Practice                 [Page 3]

    RFC 8174                 RFC 2119 Clarification                 May 2017

    3.  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]