2PLOT: plot clip - set a clip path

Usage: clip <x1> <y1> <x2> <y2>
       clip off

draws a rectangle with the given corners and sets the current clipping
path to its border. Subsequent drawing commands will only draw within
this rectangular area. In the form "clip off", the command resets the clipping path. After this command, graphics will no longer be confined
to the rectangular area specified in a previous clip command.