RRule\RRule::parseDate PHP Method

    public static function parseDate($date)
    {
        // DateTimeInterface is only on PHP 5.5+, and includes DateTimeImmutable
        if (!$date instanceof \DateTime && !$date instanceof \DateTimeInterface) {
            try {
                if (is_integer($date)) {
                    $date = \DateTime::createFromFormat('U', $date);
                    $date->setTimezone(new \DateTimeZone('UTC'));
                    // default is +00:00 (see issue #15)
                } else {
                    $date = new \DateTime($date);
                }
            } catch (\Exception $e) {
                throw new \InvalidArgumentException("Failed to parse the date");
            }
        } else {
            $date = clone $date;
            // avoid reference problems
        }
        return $date;
    }