 responsibility.        */       iterator       erase(const_iterator __position)       { return _M_h.erase(__position); }        // LWG 0000.       iterator       erase(iterator __it)       { return _M_h.erase(__it); }       //@}        /**        *  @brief Erases elements according to the provided key.        *  @param  __x  Key of element to be erased.        *  @return  The number of elements erased.        *        *  This function erases all the elements located by the given key from        *  an %unordered_