docs: def _act_on_list(self, lhs):
          '''
          Act on the following rule :
              items : items item
                    | item
          '''
          lhs[0] = []
          if len(lhs) == 3:
              lhs[0] = lhs[1]
          # lhs[len(lhs)-1] may be different from lhs[-1]
          # Yacc use some internal method to get the element, see yacc.py:240
          item = lhs[len(lhs) - 1]
          if item:
              lhs[0].append(item)