code: def join_room(self, room_id_or_alias):
          
          if not room_id_or_alias:
              raise MatrixError("No alias or room ID to join.")
  
          path = "/join/%s" % quote(room_id_or_alias)
  
          return self._send("POST", path)
docs: Performs /join/$room_id
  
          Args:
              room_id_or_alias (str): The room ID or room alias to join.