We have a use case where we want to have a set of MedicationUsage instances that are all a part of an overall MedicationUsage.

A patient is given a set of patches to apply daily.  At their next visit, they are asked "did you use the patches over the last 30 days?" and answer yes or no.  That is one MedicationUsage instance.  They are also asked "which days over the last 30 days did you actually use the patch?" and provides more discrete information and MedicationUsage instances are created for each day that they used the patch.  We want the discrete MedicationUsage instances to point to the overall MedicationUsage instance.

NOTE: In r4, partOf did include a lot of other references that were removed by a previous issue.  This issue is pointing out that we might have been over-zealous in this one instance.