Reading the sentence presented I get a feeling that the word resource may be missused as how can be a FHIR resource not be available via RESTful FHIR API? Are not all the FHIR resources supposed to be available by definition?

In that sense the next sentence: "For example, the proposed CDS Hooks decision workflow can be implemented through SMART Web Messaging." does not explain much to me as it does not give any example of such a FHIR resource.

May be I am wrong, as my experience with FHIR is very rudimental. However, the example given does not seem to be very explanatory to me either way.

Existing Wording:

Messaging exposes an API to the clinician’s scratchpad within the EHR, which may contain FHIR resources unavailable on the RESTful FHIR API.