The control element accomplishes a subclassing for a window stated by its handle. The window function is the function of a window, which completely determines the behavior of the window (and thus the reaction of the window to user inputs). This window function is replaced by another function by the Subclassing component. This function then can be freely defined in the Message event of the Subclassing control element (MS Windows API Programmierung). It is possible to either replace (StopMessage = True) or only to supplement the original window function (StopMessage = False). The latter aspect is called also Superclassing.