It is not clear how to reconcile 'In order to limit the scope of this Implementation Guide, SubscriptionTopic definitions are not defined here. Since topics are always referenced by their canonical URL, servers using FHIR R4 have no need to implement any of the functionality around topics themselves.' with the preceding section stating 'Definitionally, a Subscription requires the a SubscriptionTopic - without a resource describing the change of interest, a Subscription has no meaning and will not trigger any client notifications.' Together this would indicate that FHIR R4 clients may be able to use this specification but FHIR R4 servers would not, and that does not seem to be the intent of this IG.

(Comment 76 - imported by: Gino Canessa)