It is useful to have Howard Stearns' fix from Mantis #3613 (if it's
not in the update stream yet) or run in fullscreen mode to avoid a
weird problem under Tweak.
After loading this package, click on the Croquet button in the green
Objects catalog to refresh the choices, then drag out the
MockTurtleDemo (Master). There are several keystrokes by the little
cube drag-painter. For more information, browse the class comments
for MTurtle and MTDragger.