code: def indent(self, node, dirty=True):
          
          if node.subitems:
              return
  
          self._subitems[node.id] = node
          node.super_list_item_id = self.id
          node.parent_item = self
          if dirty:
              node.touch(True)
docs: Indent an item. Does nothing if the target has subitems.
  
          Args:
              node (gkeepapi.node.ListItem): Item to indent.
              dirty (bool): Whether this node should be marked dirty.