title: When to use DIRECTORY_SEPARATOR in PHP code?
body: <pre><code>require_once dirname(__FILE__).DIRECTORY_SEPARATOR . './../../../wp-config.php';
  require_once dirname(__FILE__).DIRECTORY_SEPARATOR.'inc/options.php';
  </code></pre>
  <p>The above code is from a plugin from the Wordpress.
  I don't understand why half of it uses <code>DIRECTORY_SEPARATOR</code>, but the other half uses <code>&quot;/&quot;</code> ?</p>