Showcase add-ins are Python modules which extend the functionality of Showcase by: 
         
            - adding menu items 
- authoring advanced environments 
- authoring custom materials 
- saving screenshots or short movies 
 add-ins can be combined with custom web browser interfaces and batch scripting to provide even greater functionality. 
         
         A Showcase add-in contains: 
               - A class derived from UserCustomization.UserCustomBase. 
               
-  A module method instantiate() which returns an instance of your newly defined add-in class derived from UserCustomization.UserCustomBase. 
                  def instantiate():
  return MyAddinCustom() 
- An optional message registration call to theMessageRegistry.register() to register your custom messages (and any associated usage documentation) with Showcase. 
               
- An optional custom message interpreter derived from MessageInterpreter.MessageInterpreter.