ADD_VP_DIRECTION_AXES displays the direction axes in the
top left-hand corner of the specified viewport.
---->(ADD_VP_DIRECTION_AXES)---|viewport|---->
This action has no options.
Use this action to display the direction axes of the specified
viewport, in the top left-hand corner of the viewport.
The axes are always displayed using depth cueing for clarity,
and a letter ("X", "Y", or "Z"), is displayed at the end of
each axis.
The following parameter sequence displays the direction axes in
the specified viewport.
ADD_VP_DIRECTION_AXES [specify viewport]
REMOVE_VP_DIRECTION_AXES interrupt action
SELECT_VP_SA subaction