public function setSkipDays(array $days)
    {
        if (count($days) > 7) {
            /**
             * @see Zend_Feed_Builder_Exception
             */
            require_once 'Zend/Feed/Builder/Exception.php';
            throw new Zend_Feed_Builder_Exception("you can not have more than 7 days in the skipDays property");
        }
        $valid = array('monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday', 'sunday');
        foreach ($days as $day) {
            if (!in_array(strtolower($day), $valid)) {
                /**
                 * @see Zend_Feed_Builder_Exception
                 */
                require_once 'Zend/Feed/Builder/Exception.php';
                throw new Zend_Feed_Builder_Exception("$day is not a valid day");
            }
        }
        $this->offsetSet('skipDays', $days);
        return $this;
    }