protected function addPeriodSelect(array &$elements, $data)
    {
        $dates = array(
            'gr2t_start_date' => $this->_('Track start'),
            'gr2t_end_date'   => $this->_('Track end'),
            'gto_valid_from'  => $this->_('Valid from'),
            'gto_valid_until' => $this->_('Valid until'),
        );
        // $dates = 'gto_valid_from';
        $this->_addPeriodSelectors($elements, $dates, 'gto_valid_from');
    }