Indicates the root element of the user interface. At design-time, the root element may be one of two things, depending upon whether the form designer or control interface editor is active:
If the form designer is active, then the root element will be the base element associated with the active TFormControl instance.
If the control interface editor is active, then the root element will be the base element for the currently-selected control interface state.
At run-time, the root element is always the base element for the global ApplicationSurface instance.