protected function get_pre_deep_keys_value( array $arr ) {
		$keys  = [];
		$value = null;

		foreach ( $arr as $key => $v ) {
			if ( is_array( $v ) ) {
				$keys[] = $key;
				list( $ks, $val ) = $this->get_pre_deep_keys_value( $v );
				$keys   = array_merge( $keys, $ks );
				$value  = $val;
			} else {
				$keys[] = $key;
				$value  = $v;
			}
		}

		return [$keys, $value];
	}