title: exclude specific path from routing in angular 2+
body: <p>My angular route config is as below:</p>
  
  <pre><code>export const routes: Routes = [
    { path: 'mgmt', ... },
    { path: 'about', ... },
    { path: '**', component: PageNotFoundCmp }
  ];
  </code></pre>
  
  <p>But now on a page, there's a link (<code>&lt;a href="/help/en/index.html" target="_blank"&gt;</code>) to help pages, which are static resources hosted on the same server. With the above route config, apparently it will be matched to others <code>**</code> - page not found.</p>
  
  <p>Let's say we cannot host help resources in another domain, is there any way to exclude <code>/help/**</code> path from angular routing? or do you think this is a valid feature request for angular to support?</p>