private function partial($id, $indent, $level)
    {
        if ($indent !== '') {
            $indentParam = sprintf(self::PARTIAL_INDENT, var_export($indent, true));
        } else {
            $indentParam = '';
        }

        return sprintf(
            $this->prepare(self::PARTIAL, $level),
            var_export($id, true),
            $indentParam
        );
    }