title: Hidden replica set do not take part in election
body: <p>I have a replica set of three server and a backup server, The backup server is made </p>
  
  <pre><code>"hidden"=true and "priority"=0`
  </code></pre>
  
  <p>My concern is when I have one of my secondary and backup server up, my secondary does not changes into primary, which means hidden server is not taking part in election, but as per the mongo document, it cannot become primary but takes part in election. Is their some extra configuration required to do so? </p>