I am not sure if the Bundle response for the first example of $docref operation contains a valid US Core DocumentReference resource, or FHIR DocumentReference resource.

The comments here:

• The meta.profile does not include US Core DocumentReference profile
• DocumentReference.created is not a valid FHIR DocumentReference element
• DocumentReference.indexed is not a valid FHIR DocumentReference element
   

I understand that $docref operation MAY return DocumentReference resources which are not conform to the US Core DocumentReference Profiles. Since this is an example in US Core IG, I think it would be better to make the example here conforming to US Core profile.