为什么 routes/web.php 文件可以不用引入命名空间

为什么 Laravel 的路由文件routes/web.php里面使用Route类不用引入命名空间就可以使用的？

<?php
/*
|--------------------------------------------------------------------------
| Web Routes
|--------------------------------------------------------------------------
|
| Here is where you can register web routes for your application. These
| routes are loaded by the RouteServiceProvider within a group which
| contains the "web" middleware group. Now create something great!
|
*/
Route::get('/', function () {
    return view('welcome');
});