What is an extended control?
OLE controls are contained within control containers. These containers (e.g., a VB form) are responsible for providing and managing a control site for each OLE control within the container. Since the container provides this and other services to a control, it maintains certain information about the control that control users may want to access and modify. A good example of this is the actual position of a control within its container. A control is contained and has no (inherent) knowledge of where it is located on a form. To present a consistent interface to a control user and to provide a way for a control container to modify the functionality of an embedded control, the OLE control standard describes an extended control. The container creates this extended control and then uses COM containment and aggregation to encapsulate the functionality of the original OLE control. Containment and Aggregation are COM techniques that are similar to the C++ concept of class composition. This allow
