Extending a Class

I found a class to extend QuickForm, but I don't think I'm setting it up right to extend it. // Error Cannot inherit from undefined class html_quickform_element // Config file require_once 'HTML/QuickForm.php'; <-- QuickForm works fine requie_once 'fckeditor.php'; // fckeditor.php Here's the top of it: /** * Custom HTML_Quickform elementtype voor FCKEditor textarea * * This elementtype buidls an FCK Editor instance for PEAR::HTML_Quick_websitform * class * * @author Jordi Backx */ class HTML_Quickform_fckeditor extends HTML_Quickform_element <-- I tried doing HTML_QuickForm::HTML_Quickform { /** * Path to FCK class * * @var string Path to PHP FCK class * @access private */ var $_sFckBasePath = NULL; . . . Am I doing this right? Or do I need to add this to the actual QuickForm files?