protected static function _parse($string) {
		if (substr_count($string, '::') !== 2) {
			throw new Exception('Possible data tampering: form signature string has wrong format.');
		}
		list($locked, $excluded) = explode('::', $string, 3);

		return [
			'locked' => unserialize(urldecode($locked)),
			'excluded' => unserialize(urldecode($excluded))
		];
	}