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RFC 8174 / READING REQUIREMENTS

Distinguish special key words from ordinary English

02

MUST, must and Must are different spellings for this convention. Only the all-capital form has the defined BCP 14 special meaning.

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RFC 8174 · § 2EXAMPLE
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Distinguish special key words from ordinary EnglishThree separate spelling comparisons show MUST, must and Must. Only MUST is entirely uppercase and has the defined special key-word meaning under this convention. Lowercase must and mixed-case Must retain normal English meanings; neither label says the entire sentence is optional. These are comparisons of text, not a network flow, and quoted words in this guide are not new protocol requirements.Compare the spelling without changing itMustNot all capitalsNormal English meaningNo special BCP 14 keyword forceThis does NOT mean the sentence is optional
03
Treat mixed case the same way.

An initial capital is not all capitals. Read the normal English and the specification’s context.

Source for this drawing: RFC 8174 · Read RFC section 2 ↗

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KEY POINT

Do not silently uppercase a requirement when paraphrasing it.

  • The special meanings apply only when the key words are in all capitals as shown in the convention.
  • Lowercase and mixed-case occurrences have their normal English meanings; RFC 8174 does not give them the special key-word meanings.
  • Ordinary English is not automatically non-normative. Decide what the surrounding specification requires, rather than changing every must to MUST or discarding every lowercase sentence.
DETAILS

These are spelling comparisons, not three steps of a protocol exchange. Quotes, examples and a document’s surrounding scope still matter: a capitalized word in a glossary or this illustration is not itself a new obligation to send a packet.

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