title: Are Helper Classes or Categories available in PHP?
body: <p>In <code>Objective-C</code> you can create a Category which allows you to add extra functionality to an existing class eg <code>NSString</code>.  In <code>Delphi</code> you can create a Helper class that again allow you to add functionality to an existing class.  in <code>Javascript</code> you can add functions to the class prototype.</p>
  
  <p>Is there anything similar available for <code>PHP</code>?</p>