title: what is the difference between __FILE__ and $_SERVER['SCRIPT_FILENAME']?
body: <pre><code>define('QA_BASE_DIR', dirname(empty($_SERVER['SCRIPT_FILENAME']) ? __FILE__ : $_SERVER['SCRIPT_FILENAME']).'/');
  </code></pre>
  
  <p>what is the difference between <code>__FILE__</code> and <code>$_SERVER['SCRIPT_FILENAME']</code> ?</p>