Network Working Group B. Leiba
Internet-Draft Huawei Technologies
Updates: 2119 (if approved) March 9, 2017
Intended status: Best Current Practice
Expires: September 10, 2017

Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words


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.

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1. Introduction

RFC 2119 specifies common key words, such as "MUST", "SHOULD", and "MAY", that may be used in protocol specifications. It says that those key words "are often capitalized," and that 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 will become part of BCP 14 when it is approved. [[RFC-Editor: Please change the previous sentence to "This document is part of BCP 14."]]

1.1. Some Notes for Reviewers (not for publication)

[[RFC-Editor: Please remove this section before publishing.]]

This update is intentionally small and focused, and quite intentionally updates, but does not replace, RFC 2119. The author considers it important to retain the reference to RFC 2119 because of the general familiarity with the number, and to phase in the use of "BCP 14". Note, though, that the References section uses the RFC numbers, not the BCP number. This is because is needs to be clear when a document has adopted this update, and the dual reference to RFC 2119 *and* this document gives that clarity.

The point has been made by some that having case be significant to the meanings of words is unusual and may be a bad idea. There is specific concern about causing confusion to readers whose native languages do not have a distinction between upper and lower case (consider Chinese and Hebrew, for example). The author believes this has been discussed and addressed, and that those maintaining this point are in the rough.

There have been suggestions that while we're here we should consider a broader BCP 14 update that also talks about proper use of the key words, when they should not be used, avoiding overuse, and so on. The author agrees, but thinks is best to keep that as a separate effort, as coming to consensus on such an update is likely to be much more difficult, and is likely to take much longer.

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. Those 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.

Authors who follow these guidelines should incorporate this phrase near the beginning of their document:

=== END ===

[CREF1]RFC Editor: Please replace "RFCxxxx", above, with a reference to this RFC number, and remove this note.

3. IANA Considerations

There are no IANA considerations for this document.

4. Security Considerations

This document is purely procedural, and 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.

Author's Address

Barry Leiba Huawei Technologies Phone: +1 646 827 0648 EMail: URI:

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