10 REM TRAP catches a BASIC error and sends the program to a handler.
20 TRAP HANDLER
30 DIM Q#(2)
40 PRINT "BEFORE"
50 PRINT Q#(9)
60 PRINT "RESUMED"
70 TRAP
80 REM Disarmed again, so this one is reported and stops the program.
90 PRINT Q#(9)
100 PRINT "NEVER SEEN"
200 LABEL HANDLER
210 PRINT "CAUGHT " + ERR(ER#) + " ON LINE " + EL#
220 RESUME NEXT