Visual Basic version 5.0 or later allows users to extend objects. Extending an object means changing the object's behavior by writing code that handles events or adds properties, methods, or events. Using this capability, end users can create customized classes by combining an ActiveX designer, a frame supplied by Visual Basic, and a code module. In a similar manner, end users can attach code to documents, creating customized documents.
Because the ActiveX designers you distribute can be customized by end users— who can make public objects from them— you need to understand the object extensions model and be aware of the types of behavior changes that are possible. See Chapter 5, "Type Information and Extended Objects," and the Automation Programmer's Reference in the Platform Software Development Kit (SDK) for more information.