/pre><p>
Note that we don't want the selector control to appear with parts showing off the
top of the grid control.  This is achieved by making the grid and the 
pane selector control children of a PictureBox control, which would clip the
Pane Selector when you attempt to move it off the top of the grid. However,
I discovered that Windows gets confused about the region of the control if 
the top coordinate is clipped, and hence the code includes a check that hides
the selector if its top coordinate would be