$worksheet
$worksheet : \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet
\PhpOffice\PhpSpreadsheet\Worksheet\Worksheet.
getCellIterator(string $startColumn = 'A', string $endColumn = null) : \PhpOffice\PhpSpreadsheet\Worksheet\RowCellIterator
Get cell iterator.
| string | $startColumn | The column address at which to start iterating |
| string | $endColumn | Optionally, the column address at which to stop iterating |