A scrolling window allows an end user to use scroll bars
to scroll the content canvas currently displayed in that window. Conceptually,
think of scrolling as moving the content canvas to change the X,Y coordinates
of the view's point of origin, thereby revealing a different part of that
canvas. Note that scrolling does not change the size of the view, merely its
location on the canvas.
A window can be scrolled horizontally only when its
display width is less than the width of the content canvas currently displayed
in the window. Similarly, it can be scrolled vertically only when its height is
less than the height of its current content canvas. (Remember that end users
can change the size of a window at runtime.)
When a window is the same size as or larger than its
current content canvas, scrolling has no effect since no portion of the canvas
is outside the current view (that is, outside the window itself).
The scroll bars on a window scroll only the window's
content canvas; however, any stacked canvases displayed in the window will move
up/down and left/right as if they were part of the content canvas. (You can
also define scroll bars on stacked canvases, but these are independent of the
window's scroll bars
