docs: def prune_if_smaller_than(self, small_size, a_or_u):
          "Prune/merge all nodes that are smaller than small_size."
          if self._prune_all_if_small(small_size, a_or_u):
              return
  
          for node in self._nodes:
              node.prune_if_smaller_than(small_size, a_or_u)
  
          self._prune_some_if_small(small_size, a_or_u)