<p>
Normal buttons are also refered to as push buttons. They are similar
to labels in appearance except they respond to the mouse or keyboard. 
<p>
When the pointer is over a push button, the button becomes highlighted
by drawing its background with a brighter color. This highlighting
indicates that the button is ready for selection. When mouse button 1
(left button) is pressed, the push button indicates that it has been
selected by changing its border to make it look pressed down. When the
mouse button is released over the button, the buttons callbacks
procedures are invoked. If the pointer is moved off of the button before
the pointer button is released, the button reverts to its normal appearance,
and releasing the mouse button has no effect. This behavior allows the user to
cancel an action. 
<p>
If a push button is configured with a keyboard accelerator, 
it can also be invoked by typing the corresponding key strokes.
<p>
