Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Reader/Xls.php
private static function readBIFF8Constant($valueData)
    {
        // offset: 0; size: 1; identifier for type of constant
        $identifier = ord($valueData[0]);

        switch ($identifier) {
            case 0x00: // empty constant (what is this?)
                $value = '';
                $size = 9;

                break;
            case 0x01: // number
                // offset: 1; size: 8; IEEE 754 floating-point value
                $value = self::extractNumber(substr($valueData, 1, 8));
                $size = 9;

                break;
            case 0x02: // string value
                // offset: 1; size: var; Unicode string, 16-bit string length
                $string = self::readUnicodeStringLong(substr($valueData, 1));
                $value = '"' . $string['value'] . '"';
                $size = 1 + $string['size'];

                break;
            case 0x04: // boolean
                // offset: 1; size: 1; 0 = FALSE, 1 = TRUE
                if (ord($valueData[1])) {
                    $value = 'TRUE';
                } else {
                    $value = 'FALSE';
                }
                $size = 9;

                break;
            case 0x10: // error code
                // offset: 1; size: 1; error code
                $value = Xls\ErrorCode::lookup(ord($valueData[1]));
                $size = 9;

                break;
        }

        return [
            'value' => $value,
            'size' => $size,
        ];
    }
private static function readBIFF8Constant($valueData)
    {
        // offset: 0; size: 1; identifier for type of constant
        $identifier = ord($valueData[0]);

        switch ($identifier) {
            case 0x00: // empty constant (what is this?)
                $value = '';
                $size = 9;

                break;
            case 0x01: // number
                // offset: 1; size: 8; IEEE 754 floating-point value
                $value = self::extractNumber(substr($valueData, 1, 8));
                $size = 9;

                break;
            case 0x02: // string value
                // offset: 1; size: var; Unicode string, 16-bit string length
                $string = self::readUnicodeStringLong(substr($valueData, 1));
                $value = '"' . $string['value'] . '"';
                $size = 1 + $string['size'];

                break;
            case 0x04: // boolean
                // offset: 1; size: 1; 0 = FALSE, 1 = TRUE
                if (ord($valueData[1])) {
                    $value = 'TRUE';
                } else {
                    $value = 'FALSE';
                }
                $size = 9;

                break;
            case 0x10: // error code
                // offset: 1; size: 1; error code
                $value = Xls\ErrorCode::lookup(ord($valueData[1]));
                $size = 9;

                break;
        }

        return [
            'value' => $value,
            'size' => $size,
        ];
    }
read BIFF8 constant value which may be 'Empty Value', 'Number', 'String Value', 'Boolean Value', 'Error Value'
section 2.5.7
returns e.g. ['value' => '5', 'size' => 9].

@param string $valueData

@return array