title: How to make a marker interface, or something similar
body: <p>I'm making a modal window service for my angular app, using the component factory resolver to load up dynamic content in the dialog box. Right now, I have it setup to allow any component to be passed into the modal window service, to be shown in the dialog box. The problem is, I only want components I "mark" to be allowed to thrown in the modal window service. So my initial thought went to an interface. But after a little research, it turns out that restricting it to an empty interface doesn't help at all because still any component can be passed in.</p>
  
  <p>I only want "marked" components to be able to be passed in because these are the same components I will mark in my app module as <a href="https://angular.io/guide/entry-components" rel="nofollow noreferrer">entry components</a>.</p>