Angular2: Export of RouterModule, Why it is required? : <p>I am learning <a href="http://angular.io" rel="noreferrer">Angular 2</a>'s  <a href="https://angular.io/docs/ts/latest/guide/ngmodule.html#app-routing" rel="noreferrer">app-routing</a> from official documentation. I am going through following piece of code. </p>

<pre><code>import { NgModule }             from '@angular/core';
import { Routes, RouterModule } from '@angular/router';

export const routes: Routes = [
  { path: '', redirectTo: 'contact', pathMatch: 'full'},
  { path: 'crisis', loadChildren: 'app/crisis/crisis.module#CrisisModule' },
  { path: 'heroes', loadChildren: 'app/hero/hero.module#HeroModule' }
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule {}
</code></pre>

<p>It creates an <code>AppRoutingModule</code> and defines <code>routes</code> for it. The part which I am not able to understand is <strong>Why do we need to export RouterModule again?</strong> I believe it's one of the core angular module and which available everywhere by import of <code>@angular/router</code>. </p>
