Is there a working sample of an ActiveX add-in for PowerDesigner?

I've been reading about ActiveX addins for PowerDesigner - here's what PD help says:

• An ActiveX add-in implements an interface that defines methods, which are invoked by PowerDesigner in order to dialog with menus and execute commands that are defined by the ActiveX.

I don't know enough about ActiveX to visualise this - are there any examples I could look at, or descriptions of them (e.g. saying what it does, what it contains, how it's implemented)?