Re: we propose that it be made more clear that (1) “contains” are free to be used for any reference within a US Core Profile as desired since the IG does not dictate when they may or may not be leveraged,  Further guidance about the general use case for contained can be found in the base FHIR specification where its use is discouraged except for a narrow defined set of circumstances.   Add section to guidance page with text:   Contained resources SHOULD NOT be used when responding to a query. The only time contained resource can be used is when the source data exists only within the context of the FHIR transaction. For example, the explicit guidance in this guide pertaining to medications.  Further guidance about the general use case for contained can be found in the base  FHIR specification     Re: ( 2) that when a developer elects to leverage a contain, the US Core Profile conformance is technically optional due to the SHOULD conformance statement in the IG. _This is already stated in the Guidance section here:  file:///Users/ehaas/Documents/FHIR/US-Core-R4/output/general-guidance.html#referencing-us-core-profiles_