Tandy 1000 Basic Reference Manual page 237

Chapter 10
I
BASIC Keywords
Example
1 0 P E N ON
2 0 ON P E N GOSUB 1 0 0 0
3 0 REM
5 0 0 END
1 0 0 0 REM P R O C E S S I N G R O U T I N E
1 1 0 0 RETURN ' 3 0
Line 10 turns on pen trapping. After each program statement is
executed, BASIC checks to see if the pen has been activated. If it
has, BASIC immediately executes the subroutine a t Line 1000.
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