Re: [EXTERNAL] Re: Response for unsupported conditional request

> A recipient not might look for these headers, and subsequently not
> take any action based on these headers for which it did not look.
> It really is as simple as that.


I'm still struggling to understand this. When I read this in RFC 9110 (Section 13.1.1.):


When an origin server receives a request that selects a representation and that request includes an If-Match header field, the origin server MUST evaluate the If-Match condition per Section 13.2 prior to performing the method.


Am I to understand that the "MUST" here actually means "MUST if the origin server decides to handle If-Match, which it is not obligated to do"?


If that's correct, how is this consistent with Section 2.2, which says


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<https://datatracker.ietf.org/doc/html/rfc2119>] [RFC8174<https://datatracker.ietf.org/doc/html/rfc8174>] when, and only when, they appear in all capitals, as shown here.


And RFC 2119 says


MUST This word, or the terms "REQUIRED" or "SHALL", mean that the definition is an absolute requirement of the specification.


How do I reconcile these seemingly contradictory statements?


Mike