just refers sf-string abnf

Author: sdatspun2

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

@@ -66,13 +66,9 @@ An idempotency key is a unique value generated by the client which the resource
 ## Syntax
 
 
-`Idempotency-Key` is an Item Structured Header {{!RFC8941}}. Its value MUST be a String (Section 3.3.3 of {{!RFC8941}}. Its ABNF is:
+`Idempotency-Key` is an Item Structured Header {{!RFC8941}}. Its value MUST be a String. Refer to Section 3.3.3 of {{!RFC8941}} for ABNF of `sf-string`:
 
     Idempotency-Key = sf-string
-    sf-string = DQUOTE *chr DQUOTE
-    chr       = unescaped / escaped
-    unescaped = %x20-21 / %x23-5B / %x5D-7E
-    escaped   = "\" ( DQUOTE / "\" )
 
 
 Clients MUST NOT include more than one `Idempotency-Key` header field in the same request.