Hot spots in custom frameworks

Question

I am creating a framework. I want to add hotspots using Interfaces. For example in the case of .Net Framework 1.1, we implement IEnumerable and IEnumerator to make a class to use foreach navigation. Can some one provide me a code snippet, where the user of a custom Framework could implement Interfaces (hot spots) sending data to the Framework, which could then be used by the Framework to do the desired work. [Note: I know how to create and implement Interface for simple uses. But I need example in the context of Frameworks! :)]

Thanks

ThirstyMind