title: what does slash double underscore slash mean? /__/
body: <p>On github i see this path to a file:</p>
  
  <pre><code>importScripts('/__/firebase/3.8.0/firebase-app.js');
  importScripts('/__/firebase/3.8.0/firebase-messaging.js');
  importScripts('/__/firebase/init.js');
  </code></pre>
  
  <p>What does the "/__/" stands for?</p>