title: Limit directive to specific host (component) in Angular
body: <p>Is is possible to limit which component can have custom directive?</p>
  
  <p><strong>For example:</strong>  </p>
  
  <pre><code>@Directive({ 
      selector: '[myHighlight]', 
      host: "my-component" //!!!!!!!!!
  })
  export class HighlightDirective {
      constructor(el: ElementRef) {  //el is my-component - can not be nothing else !!!!
         el.nativeElement.style.backgroundColor = 'yellow';
      }
  }
  
  @Component({selector: "my-component"})...
  </code></pre>
  
  <p><strong>Use case:</strong><br>
  I would like to write directive for specific third-party component. I will use that third-party component properties, so directive on another component wouldn't make any sense and would throw errors.</p>
  
  <p>That means that <code>myHighlight</code> on <code>div</code> would be ignored.</p>