code: public function getCellIterator($startColumn = 'A', $endColumn = null)
      {
          return new RowCellIterator($this->worksheet, $this->rowIndex, $startColumn, $endColumn);
      }
docs: Get cell iterator.
  
  @param string $startColumn The column address at which to start iterating
  @param string $endColumn Optionally, the column address at which to stop iterating
  
  @return RowCellIterator