The RFC119 keyword REQUIRED appears once in the specification and then only in the RFC2119 definition of keywords.

The word "required" appears 8 times in the specification and never in uppercase.

Despite that lack of uppercase required, the conformance clause reads:

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An implementation conforms to this specification if it satisfies all of the MUST or REQUIRED level requirements defined within this specification.
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The specification may have some lowercase "required"s that should be REQUIRED.