protected function _validate($value)
    {
        // Look for Ymd keys?
        if (is_array($value)) {
            $value = $this->_arrayToDate($value);
        }

        // basic date format yyyy-mm-dd
        $expr = '/^([0-9]{4})-([0-9]{2})-([0-9]{2})$/D';

        return (preg_match($expr, $value, $match) && checkdate($match[2], $match[3], $match[1]));
    }