A simple-pane with internal scrolling.
The coordinates of the origin of the area to make visible.
The dimensions of the area to make visible
The generic function ensure-area-visible ensures that the area specified by x , y , width and height , or at least part of it, is visible.
This function works only for subclasses of simple-pane that do internal scrolling (such as
editor-pane). An error is signalled if it is called with other classes.