protected function _normalize($string, array $options = []) {
		$options += [
			'clean' => false,
			'case' => false
		];
		if ($options['case']) {
			$string = strtoupper($string);
		}
		$string = strtr($string, [
			'I' => 1,
			'O' => 0,
			'S' => 5,
			'Z' => 2,
		]);

		if ($options['clean']) {
			$string = preg_replace('/[^0-9A-Z]+/', '', $string);
		}
		return $string;
	}