5.1.1 UV Medication Order template includes:
hl7:participant
"Record Target: indicates the person who's medical record holds the documentation of this medication statement. This element is only populated when the document is placed in a medical record of someone other than the patient (subject)."

It will be useful to provide better clarity to the second sentence with some use case specific examples.
For example: for use case of maternal transplacental drug administration to treat fetal tachycardia, the drug is given to the fetus through the pregnant mother - will there be two instances?
One instance for the mother for which the hl7:participant element is not populated
Another instance for the fetus for which the hl7:participant element is populated