AT&T 6300 Programmer's Manual page 403

Syntax
Remarks
PLAY
ON I OFF I STOP
Statements
PLAY ON enables PLAY(n) trapping.
PLAY OFF disables PLAY(n) trapping.
PLAY STOP suspends PLAY(n) trapping.
PLAY {ON
I
OFF
I
STOP}
PLAY ON, PLAY OFF, PLAY STOP are used
in conjunction with the ON PLAY(n)
statement.
If a PLAY OFF statement has been executed
the GOSUB is not performed and is not
remembered.
If a PLAY STOP statement has been executed
the GOSUB is not performed, but will be
performed as soon as a PLAY ON statement is
executed.
When an event trap occurs (i.e., the GOSUB is
performed), an automatic PLAY STOP is
executed so that recursive traps cannot take
place. The RETURN from the trapping
subroutine will automatically perform a PLAY
ON statement unless an explicit PLAY OFF
was performed inside the subroutine.
The RETURN "linenum" form of the
RETURN statement may be used to return to
a specific line number from the trapping
subroutine. Use this type of return with care,
however, because any other GOSUBs,
WHILEs, or FORs that were active at the time
of the trap will remain active, and errors such
as "FOR without NEXT" may result.
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