Specifies a rectangle with one corner at (x1,y1), and with width given by
x2, or h if if x2 is null, and with height given by y2, or by v if y2 is
null.
If a function has been specified using startEdit(), and neither
finishEdit() nor cancelEdit have been called, then this method will
discard the current data in and replace it with data from the edit
function.