code: def item_at_line(root_item, line):
      
      previous_item = root_item
      item = root_item
      for item in get_item_children(root_item):
          if item.line > line:
              return previous_item
          previous_item = item
      else:
          return item
docs: Find and return the item of the outline explorer under which is located
      the specified 'line' of the editor.