Following the manual for v10 Extending the application with Mongoose.
Exercise 5.2, Page 105, it has me use this on a combo box control:

I am told that the Property Class Extension does not exist and I am to click "Yes' to save it.
Then next screen appears and I populate the following attributes.

All went fine until I tested the form and the expected results were not seen. I went back to designer to clear my entries but I could find know way to do so. Also, I cannot find where the Property Class Extension is saved. I checked in IDOs and Property Class Forms. How do I unwind this so I can get back to the previous Lesson where life was good?
Regards,
Lance