Set or get the current scrollbar position. You usually will want to set up a notification
on this attribute to be notified whenever the scrollbar position changes. This allows
you to dynamically react to these changes and update another widget which your scrollbar
is determined to control.
Note that unless Scrollbar.AutoScale is to False
, this value will be in
device-independent pixels. If you want to have physical pixels instead,
you must set Scrollbar.AutoScale to False
.