Changing participation policy fires a
        "ParticipationPolicyChanged" event

def participant_policy(self, value):
        """ Changing participation policy fires a
        "ParticipationPolicyChanged" event
        """
        old_policy = self.participant_policy
        new_policy = value
        self._participant_policy = new_policy
        notify(ParticipationPolicyChangedEvent(self, old_policy, new_policy))