title: How zsh stores history? History file format
body: <p>I am not sure if I fully understand how zsh stores its history. Example line:</p>
  
  <p><code>: 1458291931:0;ls -l</code></p>
  
  <p>I guess we have here:</p>
  
  <ul>
  <li>timestamp: <strong>1458291931</strong></li>
  <li>command: <strong>ls -l</strong></li>
  </ul>
  
  <p>but what this mystical <strong>0</strong> in between means?</p>