The container is the area in which the knob can move.  It is actually the
select box of the gadget.  The size of the container, like that of any
other gadget select box, can be relative to the size of the window.  The
position of the container can be relative to any of the Intuition window's
border.

Clicking in the container around the knob will increment or decrement the
value of the gadget (the pot variables) by the appropriate amount
(specified in the body variables).  The knob will move towards the point
clicked when action is taken.