item-0 at level 0: GroupLabel.UNSPECIFIED: group _root_
  item-1 at level 1: DocItemLabel.TITLE: Introduction
    item-2 at level 2: DocItemLabel.PARAGRAPH: This is the first paragraph of the introduction.
    item-3 at level 2: DocItemLabel.SECTION_HEADER: Background
      item-4 at level 3: DocItemLabel.PARAGRAPH: Some background information here.
      item-5 at level 3: GroupLabel.LIST: group list
        item-6 at level 4: DocItemLabel.LIST_ITEM: First item in unordered list
        item-7 at level 4: DocItemLabel.LIST_ITEM: Second item in unordered list
      item-8 at level 3: GroupLabel.ORDERED_LIST: group ordered list
        item-9 at level 4: DocItemLabel.LIST_ITEM: First item in ordered list
        item-10 at level 4: DocItemLabel.LIST_ITEM: Second item in ordered list