Class box represents a simple rectangle. It is the
simples graphical
object of PCE.
Boxes may have rounded corners (see box->radius);
their line may have some
graphical->texture
(dash-pattern) and their inside may be filled (see box->fill).
|{foreground,background}*Defaults: @nil (transparent)
<->radius.
A value of 0 implies square corners.
Defaults: 0 (not rounded)