WinStudio
Read-only. Specifies the base form from which an extended form has been created.
This property is displayed only for an extended form, that is, a form that has been created as an extension of another form. For more information, see About Creating New Forms by Extension.
To view the details about the extended form, including the components, event handlers, and variables belonging to both the base form and the extended form, click the ellipsis (...) button.
About Creating New Forms by Extension
Extended Form Details Dialog Box