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 ON KEY(n%) GOSUB {linenumber | linelabel}
 
 Usage Notes
   ■ Use the KeyDown, KeyPress, and KeyUp events to handle keyboard input
     with forms. ON KEY will not work when forms are showing.
     See: ◄KeyDown Event►  ◄KeyPress Event►  ◄KeyUp Event►
 
   ■ To use the ON KEY statement with forms, you must first unload or hide
     any visible forms. See: ◄HIDE Method►  ◄UNLOAD Statement►
 
   ■ 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►
 
   ■ The RETURN linenumber or RETURN linelabel forms of RETURN can be used
     to return to a specific line from a trapping routine. However, any
     GOSUB, WHILE, or FOR statements active at the time of the trap remain
     active. Visual Basic may generate error messages such as "NEXT without
     FOR."
 
   ■ Keys are processed in the following order:
     • The line printer's echo-toggle key is processed.
       Defining this key as a user-defined key trap does not prevent
       characters from being echoed to the line printer when pressed.
     • Function keys and the arrow keys are examined.
       Defining a function key or arrow key as a user-defined key trap has
       no effect because these keys are predefined.
     • The user-defined keys are examined.
 
   ■ The ON KEY statement can trap any key, including Break or System Reset
     (Ctrl+Alt+Del). This makes it possible to prevent accidentally breaking
     out of a program or rebooting the machine.
 
   ■ The ON KEY statement specifies only the start of an event-trapping
     routine. The KEY statement determines whether the routine is called
     and how events are handled when trapping is off. See: ◄KEY Statement►
 
   ■ If an event occurs in a procedure, a RETURN linenumber or RETURN
     linelabel statement cannot get back into the procedure, because the
     line number or label must be in the module-level code.
 
   ■ After a key is trapped, the information specifying which key was
     trapped is no longer available. This means that you cannot subsequently
     use an INPUT statement or INKEY$ function to find out which key caused
     the trap. Because you do not know which keypress caused the trap,
     you must create a different event-handling routine for each key you
     want to trap.