Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Writer/Xls/BIFFwriter.php
public function writeData($data)
    {
        if (strlen($data) - 4 > $this->limit) {
            $data = $this->addContinue($data);
        }
        $this->_datasize += strlen($data);

        return $data;
    }
public function writeData($data)
    {
        if (strlen($data) - 4 > $this->limit) {
            $data = $this->addContinue($data);
        }
        $this->_datasize += strlen($data);

        return $data;
    }
General storage function like append, but returns string instead of modifying $this->_data.

@param string $data binary data to write

@return string