code: def InsertArg(self, string="", **_):
      
      if self.state == "LIST_ARG":
        self.list_args.append(string)
      elif self.current_expression.AddArg(string):
        # This expression is complete
        self.stack.append(self.current_expression)
        self.current_expression = self.expression_cls()
        # We go to the BINARY state, to find if there's an AND or OR operator
        return "BINARY"
docs: Insert an arg to the current expression.