public static function compareTimezonesByOffset($a, $b) {

		$dta = new DateTime(null, new DateTimeZone($a));
		$dtb = new DateTime(null, new DateTimeZone($b));

		if ($dta->getOffset() == $dtb->getOffset()) {
			return (strcmp($a, $b) < 0) ? -1 : 1;
		}
		return ($dta->getOffset() < $dtb->getOffset()) ? -1 : 1;
	}