Start
  par_item
    '('@(1:1-1:2)
    par_item
      '('@(1:2-1:3)
      par_empty
        '('@(1:3-1:4)
        ')'@(1:4-1:5)
      ')'@(1:5-1:6)
    ')'@(1:6-1:7)
  Eof@(2:1-2:1)=''