/**
  * Renders a $variable for an $output
  *
  * @param  string       $variable  Variable to render
  * @param  string       $output    'html': HTML rendering, 'text': TEXT rendering
  * @param  boolean      $rounded   Round column values ?
  * @return string|null
  */
 public function renderColumn($variable, $output = 'html', $rounded = false)
 {
     $html = $output == 'html';
     switch ($variable) {
         case 'rate':
         case 'original_rate':
         case 'tax_amount':
             $ret = $this->renderItemRate($variable, $html, $rounded);
             break;
         case 'first_rate':
         case 'first_original_rate':
         case 'first_tax_amount':
             if (property_exists($this, $variable)) {
                 $ret = cbpaidMoney::getInstance()->renderPrice($this->{$variable}, $this->currency, $html, $rounded);
             } else {
                 $ret = null;
             }
             break;
         case 'validity_period':
             if ($this->start_date && $this->stop_date && $this->start_date != '0000-00-00 00:00:00' && $this->stop_date != '0000-00-00 00:00:00') {
                 $startDate = cbFormatDate($this->start_date, 0, false);
                 $stopDate = cbFormatDate($this->stop_date, 0, false);
                 $ret = htmlspecialchars($startDate);
                 if ($startDate != $stopDate) {
                     $ret .= ($html ? ' - ' : ' - ') . htmlspecialchars($stopDate);
                 }
             } else {
                 $ret = null;
             }
             break;
         case 'tax_rule_id':
             if ($this->tax_rule_id && is_callable(array('cbpaidTaxRule', 'getInstance'))) {
                 $ret = cbpaidTaxRule::getInstance((int) $this->tax_rule_id)->getShortCode();
             } else {
                 $ret = null;
             }
             break;
         case 'ordering':
             if ($this->payment_item_id) {
                 $paymItem = $this->_paymentBasket->getPaymentItem($this->payment_item_id);
                 if ($paymItem) {
                     $ret = htmlspecialchars($paymItem->ordering);
                 } else {
                     $ret = null;
                 }
             } else {
                 $ret = null;
             }
             break;
         case 'discount_amount':
         case 'first_discount_amount':
             $ret = null;
             break;
         case 'quantity':
         case 'artnum':
         case 'description':
         case 'discount_text':
         default:
             $ret = htmlspecialchars($this->get($variable));
             break;
     }
     return $ret;
 }