code: private function getTemporaryFolder()
      {
          $tempFolder = sys_get_temp_dir() . '/phpspreadsheet';
          if (!is_dir($tempFolder)) {
              if (!mkdir($tempFolder) && !is_dir($tempFolder)) {
                  throw new \RuntimeException(sprintf('Directory "%s" was not created', $tempFolder));
              }
          }
  
          return $tempFolder;
      }
docs: Returns the temporary directory and make sure it exists.
  
  @return string