title: Angular2: What is ng.probe and ng.coreTokens?
body: <p>I am working on a project build on <a href="https://angular.io" rel="nofollow noreferrer">Angular 2</a>. I am going through it's source code. I came across the following piece of code:</p>
  
  <pre><code>let _ng = (&lt;any&gt;window).ng;
  (&lt;any&gt;window).ng.probe = _ng.probe;
  (&lt;any&gt;window).ng.coreTokens = _ng.coreTokens;
  </code></pre>
  
  <p>I don't know what are <code>ng</code>, <code>ng.probe</code> and <code>ng.coreTokens</code> and for what purpose they are being used in angular 2. Can anyone please shed some lights on these? I googled these terms as well, but couldn't find any helpful elaboration.  I am new to the world of Angular 2. Thanks</p>