Performs different actions as part of several statements:
 
    - Enables error trapping when used with the ON ERROR statement.
    - Enables event trapping when used with the event ON statements
      (COM ON, KEY ON, PEN ON, PLAY ON, STRIG ON, and TIMER ON).
    - Specifies an event to trap when used with the ON event statements
      (ON COM, ON KEY, ON PEN, ON PLAY, ON STRING, and ON TIMER).
    - Specifies an expression to evaluate when used with the ON...GOSUB
      and ON...GOTO statements.
 
See Also    <COM, ON COM>      <KEY, ON KEY>        <ON ERROR>
            <ON...GOSUB, ON...GOTO>                 <PEN, ON PEN>
            <PLAY, ON PLAY>    <STRIG, ON STRIG>    <TIMER, ON TIMER>