code: def multizone_member_added(self, member_uuid):
          
          casts = self._casts
          if member_uuid not in casts:
              casts[member_uuid] = {'listeners': [],
                                    'groups': set()}
          casts[member_uuid]['groups'].add(self._group_uuid)
          for listener in list(casts[member_uuid]['listeners']):
              listener.added_to_multizone(self._group_uuid)
docs: Handle added audio group member.