title: Angular2 Declaring a directive's selector to require a text input
body: <p>I have just created a number directive : </p>
  
  <pre><code>@Directive({
    selector: '[ngModel][number]'
  })
  export class NumberDirective  {...}
  </code></pre>
  
  <p>I would like my selector to be even more specific and requires a text input :</p>
  
  <pre><code>&lt;input type="text" [(ngModel)]="..." [number]="..."&gt;
  </code></pre>