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 PEN {ON | OFF | STOP}
 
 Usage Notes
   ■ If your program contains event-handling statements and you are compiling
     from the BC command line, use the /W or /V option. If you do not use
     these options and your program contains event traps, Visual Basic
     generates the error message, "ON event without /V or /W on command
     line." See: ◄BC Command-Line Options►
 
   ■ PEN ON enables lightpen-event trapping. A lightpen event occurs
     whenever the lightpen is activated by pressing the tip to the screen
     or pressing the touch ring. If a lightpen event occurs after a PEN ON
     statement, the routine specified in the ON PEN statement is
     executed.
 
   ■ PEN OFF disables lightpen-event trapping so no trapping takes place
     until another PEN ON statement is executed. Events occurring while
     trapping is off are ignored.
 
   ■ PEN STOP suspends lightpen-event trapping so no trapping takes place
     until a PEN ON statement is executed. Any ON PEN events that occur while
     trapping is suspended are remembered and processed when the next PEN ON
     statement is executed. However, remembered events are lost if PEN OFF
     is executed.
 
   ■ When a lightpen event trap occurs (that is, the GOSUB is performed),
     an automatic PEN STOP is executed so that recursive traps cannot take
     place. The RETURN from a trapping routine automatically executes
     a PEN ON statement unless an explicit PEN OFF was performed inside
     the routine.
 
   ■ PEN ON must be executed before you use the PEN function. If you try
     to execute the PEN function when the lightpen is off, Basic generates
     the error message, "Illegal function call."