Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Cell/DataType.php
public static function checkString($pValue)
    {
        if ($pValue instanceof RichText) {
            // TODO: Sanitize Rich-Text string (max. character count is 32,767)
            return $pValue;
        }

        // string must never be longer than 32,767 characters, truncate if necessary
        $pValue = StringHelper::substring($pValue, 0, 32767);

        // we require that newline is represented as "\n" in core, not as "\r\n" or "\r"
        $pValue = str_replace(["\r\n", "\r"], "\n", $pValue);

        return $pValue;
    }
public static function checkString($pValue)
    {
        if ($pValue instanceof RichText) {
            // TODO: Sanitize Rich-Text string (max. character count is 32,767)
            return $pValue;
        }

        // string must never be longer than 32,767 characters, truncate if necessary
        $pValue = StringHelper::substring($pValue, 0, 32767);

        // we require that newline is represented as "\n" in core, not as "\r\n" or "\r"
        $pValue = str_replace(["\r\n", "\r"], "\n", $pValue);

        return $pValue;
    }
Check a string that it satisfies Excel requirements.

@param null|RichText|string $pValue Value to sanitize to an Excel string

@return null|RichText|string Sanitized value