ON PEN                   Trap for Light Pen Activity

 ON PEN GOSUB {linenum | linelabel}

    Establishes a subroutine to which Turbo Basic will branch if it
    detects light pen activity. The trap must also be turned on by means
    of a PEN ON statement.

     linenum    The first line of a pen-handling subroutine. Setting
                linenum to 0 disables trapping.

   linelabel    A label identifying the first line of a pen-handling
                routine.

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      Notes:    When activity is detected, Turbo Basic branches to the
                specified subroutine and temporarily suspends trapping (by
                means of an implicit PEN STOP statement). Trapping
                automatically resumes when a RETURN from the handling
                subroutine is executed (unless the handler explicitly
                performs a PEN OFF or PEN STOP).

                With event trapping in effect, Turbo Basic checks for the
                specified event after each program statement. The $EVENT
                metastatement can be used to turn event trapping on and
                off at specified points within a program.