@Component({
selector: 'hero-detail',
template: `
<p *ngIf="hero">

    <h2>{{hero.name}} details!</h2>
    <p><label>id: </label>{{hero.id}}</p>
    <p>
      <label>name: </label>
      <input [(ngModel)]="hero.name" placeholder="name"/>
    </p>

</p>
`
})
中的selector是干什么用的？