10 REM A stray NEXT with nothing open behaves like the plain-FOR case: the
20 REM FOR EACH's own NEXT closes it cleanly, and a second one errors.
30 GEN ONE(N#)
40     EMIT N#
50 END GEN
60 FOR EACH O# IN ONE(1)
70     PRINT O#
80 NEXT O#
90 NEXT O#
100 PRINT "UNREACHABLE"