code: public function createSheet($sheetIndex = null)
      {
          $newSheet = new Worksheet($this);
          $this->addSheet($newSheet, $sheetIndex);
  
          return $newSheet;
      }
docs: Create sheet and add it to this workbook.
  
  @param null|int $sheetIndex Index where sheet should go (0,1,..., or null for last)
  
  @throws Exception
  
  @return Worksheet