The current definition of Encounter.participant.period is "The period of time that the specified participant was present during the encounter. These can overlap or be sub-sets of the overall encounters period"

This reads as if the participant needs to be physically present. For example, would there be multiple participants for the same person (e.g. Attending Physician) representing each time period the participant is with the patient? What about others, such as a pathologist, who may never see the patient face to face? Are they still considered participants without a period populated?