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.
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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.
-
The words have the meanings specified herein only when they are in all capitals.
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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 ===
Key Words Quick Reference
| Keyword | Meaning | Requirement Level |
|---|---|---|
| MUST | Absolute requirement | Mandatory |
| MUST NOT | Absolute prohibition | Mandatory prohibition |
| REQUIRED | Absolute requirement | Mandatory |
| SHALL | Mandatory requirement | Mandatory |
| SHALL NOT | Mandatory prohibition | Mandatory prohibition |
| SHOULD | Strong recommendation | Recommended |
| SHOULD NOT | Strong non-recommendation | Not recommended |
| RECOMMENDED | Recommended practice | Recommended |
| NOT RECOMMENDED | Not recommended practice | Not recommended |
| MAY | Optional | Optional |
| OPTIONAL | Completely optional | Optional |
Important Note: Only the UPPERCASE form has the special meaning defined above. Lowercase forms (such as must, should, may) are ordinary English words and do not have the normative meaning defined in RFC 2119.