If the Invisible value of a Plot is non-zero, then all the Plot methods which normally
generate graphical output do not do so (you can think of them drawing with
" ). Such methods do, however, continue to do all the calculations which would be
needed to produce the graphics. In particular, the bounding box enclosing the graphics
is still calculated and can be retrieved as normal using astBoundingBox. The default
value is zero, resulting in all methods drawing graphics as normal, using visible ink.