Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
private function writeLabelSst($row, $col, $str, $xfIndex)
    {
        $record = 0x00FD; // Record identifier
        $length = 0x000A; // Bytes to follow

        $str = StringHelper::UTF8toBIFF8UnicodeLong($str);

        // check if string is already present
        if (!isset($this->stringTable[$str])) {
            $this->stringTable[$str] = $this->stringUnique++;
        }
        ++$this->stringTotal;

        $header = pack('vv', $record, $length);
        $data = pack('vvvV', $row, $col, $xfIndex, $this->stringTable[$str]);
        $this->append($header . $data);
    }
private function writeLabelSst($row, $col, $str, $xfIndex)
    {
        $record = 0x00FD; // Record identifier
        $length = 0x000A; // Bytes to follow

        $str = StringHelper::UTF8toBIFF8UnicodeLong($str);

        // check if string is already present
        if (!isset($this->stringTable[$str])) {
            $this->stringTable[$str] = $this->stringUnique++;
        }
        ++$this->stringTotal;

        $header = pack('vv', $record, $length);
        $data = pack('vvvV', $row, $col, $xfIndex, $this->stringTable[$str]);
        $this->append($header . $data);
    }
Write a string to the specified row and column (zero indexed).
This is the BIFF8 version (no 255 chars limit).
$format is optional.

@param int $row Zero indexed row
@param int $col Zero indexed column
@param string $str The string to write
@param mixed $xfIndex The XF format index for the cell