use canned boilerplate

Author: mnot

draft-ietf-httpapi-idempotency-key-header.md

@@ -51,7 +51,7 @@ For many use cases of HTTP APIs, duplicated resources are a severe problem from
 
 ##  Notational Conventions
 
-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, and without quotes.
+{::boilerplate bcp14-tagged}
 
 This specification uses the Augmented Backus-Naur Form (ABNF) notation of {{!RFC5234}} and includes, by reference, the IMF-fixdate rule as defined in Section 7.1.1.1 of {{!RFC7231}}.