ScrollBarTrough

The ScrollBarTrough is the area that the ScrollBarSlider moves around in.
Depending on the button you use in the ScrollBarTrough, you can scroll a window 
a page at a time or scroll an arbitrary amount. The direction of the scroll 
depends on which side of the ScrollBarSlider you click on.

A click in the ScrollBarTrough with the first mouse button scrolls the contents 
of the window a page at a time. If you keep the button down, the contents 
repeatedly scroll a page at a time until the you release the button or the 
window's contents scroll to one extreme.

If you click with the middle button, the contents of the window scroll so that 
the slider moves to where you clicked inside the ScrollBarTrough. Thus, you can
scroll an arbitrary amount to any relative position in the ScrolledWindow's 
contents.

See also: ScrollBar, ScrollBarArrow, ScrollBarSlider, ScrolledWindow
