for_each_head(const function<void(handle_t)>& iteratee) const;          /// For each item other than the head in the component headed by the given     /// handle, calls the iteratee with the that other item. Does not call the     /// iteratee for single-item components.     void for_each_other_member(handle_t head, const function<void(handle_t)>& iteratee) const;          /// For each item