public function showAppointment($value)
    {
        if (! $value) {
            return $this->_('Unknown');
        }
        if ($value instanceof \Gems_Agenda_Appointment) {
            $appointment = $value;
        } else {
            $appointment = $this->loader->getAgenda()->getAppointment($value);
        }
        if ($appointment instanceof \Gems_Agenda_Appointment) {
            if (! $this->menu instanceof \Gems_Menu) {
                $this->menu = $this->loader->getMenu();
            }
            $menuItem = $this->menu->findAllowedController('appointment', 'show');
            if ($menuItem) {
                if (! $this->request) {
                    $this->request = \Zend_Controller_Front::getInstance()->getRequest();
                }
                $href = $menuItem->toHRefAttribute(
                        array('gap_id_appointment' => $appointment->getId()),
                        $this->request
                        );
                if ($href) {
                    return \MUtil_Html::create('a', $href, $appointment->getDisplayString());
                }
            }
            return $appointment->getDisplayString();
        }

        return $value;
    }