title: CodeIgniter3: Why would $_SERVER['CI_ENV'] ever be set in the first place?
body: <p>I see that in their default installation, their index.php has this: </p>
  
  <pre><code>define('ENVIRONMENT', isset($_SERVER['CI_ENV']) ? $_SERVER['CI_ENV'] : 'development');
  </code></pre>
  
  <p>Why would <code>CI_ENV</code> ever <em>already</em> be set within the <code>$_SERVER</code> array?</p>