Since

C++17

The associative containers (map, set, multimap and multiset) support extracting and re-inserting nodes from the container. Those operations use the container's node_handle type, which is an alias for a _Node_handle<...> type. You should always use the container's node_handle type (e.g. std::set<int>node_handle) to refer to these types, not the non-standard internal _Node_handle names.