Add guidance about how to handle unrecognized query params, well-known but unsupported headers, & unrecognized fields in a request body

Regarding header parameters, the guidelines say:

DO NOT fail a request that contains an unrecognized header. Headers may be added by API gateways or middleware and this must be tolerated.

Regarding query parameters, the guidelines say:

DO return an error if the client specifies any parameter not supported by the service.

However, this last sentence is not mentioned in a generic context but specifically in the context of the query parameters used to query collections (e.g. filter, orderBy, etc.).

💡 It would be great to have explicit guidance about how services should handle the following:

1. Unrecognized query parameters, i.e., Does the guidance above extrapolate to any unsupported query parameter or does it not? Is it a problem that adding arbitrary query parameters to a URL is a common (albeit hacky) way to circumvent caches?
2. Well-known but unsupported header parameters, e.g., If-Match, If-None-Match, etc. If a client specifies them but the service does not support them, should this result in an error so as to not return a misleading response? Or does the guidance above about ignoring unrecognized headers still applies?
3. Unrecognized fields in a request body, i.e. Should they be ignored or should they result in an error?