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ON PEN                   Trap for Light Pen Activity

 ON PEN GOSUB {linenum | linelabel}

    Establishes a subroutine to which QuickBASIC 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.

   ----------------------------------------------------------------------

      Notes:    {linenum | linelabel} must be defined at the main program
                level.

                When activity is detected, QuickBASIC 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).

                All event trapping is temporarily disabled when QuickBASIC
                is executing an error-handling routine (established via an
                ON ERROR statement).

                If the "Checking Between Statements" option is in effect,
                QB checks after each statement. If the "Event Trapping"
                option is selected, QB checks after each new program line.
                If neither option is selected, no trapping takes place.

                For command-line compilation, /v enables checking after
                each statement, and /w enables checking after each new
                line. If neither switch is used, no trapping takes place.