public static function convert($date, $from = 'UTC', $to = 'UTC', $format = null)
    {
        $format = $format ?: self::$format;

        $from = new \DateTimeZone($from);
        $to   = new \DateTimeZone($to);
        $date = new static($date, $from);

        $date = $date->setTimezone($to);

        return $date->format($format, true);
    }