title: What exactly does a selector do in angular 2?
body: <p>What does the selector do in this case?</p>
  
  <pre><code>import { Component } from '@angular/core';
  import { HighlightDirective } from './highlight.directive';
  
  @Component({
    selector: 'my-app',
    templateUrl: 'app/app.component.html',
    directives: [HighlightDirective]
  })
  export class AppComponent { }
  </code></pre>
  
  <p>And what does it do in this case?</p>
  
  <pre><code>@Directive({
    selector: '[myHighlight]',
    host: {
      '(mouseenter)': 'onMouseEnter()',
      '(mouseleave)': 'onMouseLeave()'
    }
  })
  </code></pre>