By default, the ExtendedContainerWnd property is "Afx:*\AfxWnd*\AfxWnd*". The ExtendedContainerWnd property has mostly provided for dBASE Plus support, but it may be useful for other non-standard containers or environments. The ExtendedContainerWnd property contains a list of parent class name to be ignored by the component when it performs layout of the other components on the form. Because dBASE Plus environment places every new ActiveX inside a new container, you can not get access through the form's objects using the IOleContainer::EnumObjects, as it would list the component only. In this case, we have provided the ExtendedContainerWnd property that provides support of eXSlitBar component on dBASE Plus environment.  

For instance, if having the following form in design mode:

Internally, the hierarchy windows of a eXSplitBar inside a dBASE Plus form shows as bellow.

So as the parents of eXSplitBar are "Afx:...\AfxWnd...\AfxWnd..."and so the ExtendedContainerWnd property is "Afx:*\AfxWnd*\AfxWnd*".

If future generations of dBASE Plus will change the hierarchy of the windows inside the form, the ExtendedContainerWnd property may need to be changed.