title: What does "$td" stand for in the documentation of PHP's mcrypt extension?
body: <p><a href="http://php.net/manual/en/function.mcrypt-module-open.php" rel="nofollow">http://php.net/manual/en/function.mcrypt-module-open.php</a></p>
  
  <pre><code>&lt;?php
      $td = mcrypt_module_open(MCRYPT_DES, '',
          MCRYPT_MODE_ECB, '/usr/lib/mcrypt-modes');
  
      $td = mcrypt_module_open('rijndael-256', '', 'ofb', '');
  ?&gt;
  </code></pre>
  
  <p>In the documentation, it is described as an "encryption descriptor" in <code>mcrypt_enc_get_iv_size()</code>'s page, but that's as far as I got.</p>
  
  <p>It's bugging me that it isn't <code>$ed</code> :(</p>