public function renderDefaultValue($value)
    {
        if ($value === null) {
            return 'null';
        }

        // special numbers which are usually used in octal or hex notation
        static $specials = [
            // file permissions
            '420' => '0644',
            '436' => '0664',
            '438' => '0666',
            '493' => '0755',
            '509' => '0775',
            '511' => '0777',
            // colors used in yii\captcha\CaptchaAction
            '2113696' => '0x2040A0',
            '16777215' => '0xFFFFFF',
        ];
        if (isset($specials[$value])) {
            return $specials[$value];
        }

        return $value;
    }