public function checkoutHTML()
    {
        if (empty($this->coObjects)) {
            $this->initCheckout();
        }
        $dir = dirname(__FILE__);

        //Require the CheckoutHTML interface/abstract class
        include_once $dir.'/checkout/checkouthtml.intf.php';

        //Iterate over all .class.php files in
        $html = "\n";
        foreach ($this->coObjects as $cObj) {
            if (!self::$debug) {
                ob_start();
            }
            if ($cObj instanceof CheckoutHTML) {
                $html .= $cObj->toHTML() . "\n";
            }
            if (!self::$debug) {
                ob_end_clean();
            }
        }

        return $html;
    }