docs: def message(self):
          """Dictionary representation of the Event appropriate for JSON-encoding."""
          return {
              'timestamp': time.mktime(self.timestamp.timetuple())*1e3 + self.timestamp.microsecond/1e3,
              'group': self.group_pk,
              'participant': None if not self.participant else self.participant.code,
              'channel': self.channel,
              'value': self.value
          }