Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Style/NumberFormat.php
public static function builtInFormatCode($pIndex)
    {
        // Clean parameter
        $pIndex = (int) $pIndex;

        // Ensure built-in format codes are available
        self::fillBuiltInFormatCodes();

        // Lookup format code
        if (isset(self::$builtInFormats[$pIndex])) {
            return self::$builtInFormats[$pIndex];
        }

        return '';
    }
public static function builtInFormatCode($pIndex)
    {
        // Clean parameter
        $pIndex = (int) $pIndex;

        // Ensure built-in format codes are available
        self::fillBuiltInFormatCodes();

        // Lookup format code
        if (isset(self::$builtInFormats[$pIndex])) {
            return self::$builtInFormats[$pIndex];
        }

        return '';
    }
Get built-in format code.

@param int $pIndex

@return string