Invoice Code Problem.

In customer_invoice.php page there is a function check_quantites(). whose code given below:-

function check_quantities()
{
    $ok =1;
    foreach ($_SESSION['Items']->line_items as $line_no=>$itm) {
        if (isset($_POST['Line'.$line_no])) {
            if($_SESSION['Items']->trans_no) {
                $min = $itm->qty_done;
                $max = $itm->quantity;
            } else {
                $min = 0;
                $max = $itm->quantity - $itm->qty_done;
            }
            if (check_num('Line'.$line_no, $min, $max)) {
                $_SESSION['Items']->line_items[$line_no]->qty_dispatched =
                    input_num('Line'.$line_no);
            }
            else {
                $ok = 0;
            }
               
        }

        if (isset($_POST['Line'.$line_no.'Desc'])) {
            $line_desc = $_POST['Line'.$line_no.'Desc'];
            if (strlen($line_desc) > 0) {
                $_SESSION['Items']->line_items[$line_no]->item_description = $line_desc;
            }
        }
    }
return $ok;
}

In above code please give me explaination about if (isset($_POST['Line'.$line_no])) {.

How $_POST['Line'.$line_no] (Line No. - 5) works, means what does it means. what will be returned value.

Waiting for very quick response.

===============

Sumit Singh