title: Not a known element in angular even when using NO_ERRORS_SCHEMA
body: <p>I have and Angular Popup Component used as follows (<a href="https://stackblitz.com/edit/angular-jwpun3" rel="nofollow noreferrer">Online Example</a>):</p>
  
  <pre><code>&lt;popup&gt;
    &lt;anchor&gt;
      Menu        
    &lt;/anchor&gt;
    &lt;window&gt;
      &lt;ul&gt;
        &lt;li&gt;Item 1&lt;/li&gt;           
        &lt;li&gt;Item 2&lt;/li&gt;
      &lt;/ul&gt;
    &lt;/window&gt;
  &lt;/popup&gt;
  </code></pre>
  
  <p>An the component template is:</p>
  
  <pre><code>&lt;a class="anchor" (click)="toggle()"&gt;
    &lt;ng-content select="anchor"&gt;&lt;/ng-content&gt;
  &lt;/a&gt;
  &lt;div class="window" [hidden]="!active"&gt;
    &lt;ng-content select="window"&gt;&lt;/ng-content&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I am getting the following error:</p>
  
  <pre><code>Template parse errors: 'anchor' is not a known element:    
  1. If 'anchor' is an Angular component, then verify that it is part of this module.    
  2. To allow any element add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component. 
  </code></pre>
  
  <p>The Popup Module already has NO_ERRORS_SCHEMA:</p>
  
  <pre><code>import { NgModule, NO_ERRORS_SCHEMA } from '@angular/core';
  import { CommonModule } from '@angular/common';  
  import { PopupComponent} from './popup.component';
  
  @NgModule({  
    declarations: [PopupComponent],      
    imports: [CommonModule],  
    exports: [PopupComponent],
    schemas: [NO_ERRORS_SCHEMA]
  })
  
  export class PopupModule {}
  </code></pre>
  
  <p>And the PopupComponent is:</p>
  
  <pre><code>import { Component, Input } from '@angular/core';
  
  @Component({
    selector: 'popup',
    templateUrl: './popup.component.html'
  })
  
  export class PopupComponent {
    @Input() active: boolean = false;
    toggle() {
      this.active = !this.active;
    }
  }
  </code></pre>
  
  <p>What am I missing?</p>