I noticed that DocumentReference.subject is set to 0..0; the .subject element may still be useful for subjects that are not patient. It seems that the subject should be restricted to not be a Patient?
Practitioner -- this is individual, so I wonder if we really want NPFS to also be (non practitioner)?
Group -- groups can be made up of Patients. So it is not clear how we would allow Group, but not allow Groups of Patients.
Device -- often a Device is associated with a Patient, although many Devices are just Devices. Allowing Device might be the most clear use-case.
All this said. I am not clear that we should allow something in subject. Seems we should have a positive use-case to drive deviation from 0..0
Note that in the future, using FHIR R5, subject can be a reference to ANY kind of Resource. This is just mentioned as foreshadowing, it should not be part of the current profile.
Should this be an open issue?