item-0 at level 0: unspecified: group _root_
  item-1 at level 1: section: group sheet: Sheet1
    item-2 at level 2: table with [7x3]
  item-3 at level 1: section: group sheet: Sheet2
    item-4 at level 2: table with [9x4]
    item-5 at level 2: table with [5x3]
    item-6 at level 2: table with [5x3]
  item-7 at level 1: section: group sheet: Sheet3
    item-8 at level 2: table with [7x3]
    item-9 at level 2: table with [7x3]