Each ActiveX designer has a design-time component and a run-time component. The design-time component, or visual designer, is an embedded, in-place activated object that is invoked in the host's environment. Through its visual user interface, end users can write code and change properties, methods, and events to create an executable application.
The run-time component is the customized object that the visual designer creates. When the end user builds the application, the ActiveX designer saves the information necessary to run it. At run time, the system uses the saved information to load instances of the run-time object.
ActiveX designers are usually distributed in dynamic-link libraries (.dlls). However, if an ActiveX designer is also an ActiveX control, it can be distributed in an .ocx file instead.
The ActiveX designer model allows for flexibility in implementation. While all ActiveX designers must be embedded ActiveX components, must register as designers, and must provide a visual design-time interface, you still must decide which features to provide in the user interface and how to structure the run-time objects that users create.