什么意思* @param数组|字符串| \闭包$ middleware

Question

I'm in Laravel 5.6, Controller.php abstract class with Illuminate\Routing namespace and I would like know what kind of parameter is specified in line 19 to declared method in line 23.

I know what closure and middleware are but I don't know what this line means.

16 /*
17 * Register middleware on the controller.
18 *
19 * @param  array|string|\Closure  $middleware
20 * @param  array   $options
21 * @return \Illuminate\Routing\ControllerMiddlewareOptions
22 */
23 public function middleware($middleware, array $options = []){
24    foreach ((array) $middleware as $m) {
25       $this->middleware[] = [
26          'middleware' => $m,
27          'options' => &$options,
28       ];
29    }
30    return new ControllerMiddlewareOptions($options);
31 }