From the NannyMUD documentation

LAST CHANGE

2001-08-12

FUNCTION

NAME
        exit - Call when a living object leaves a room.


LOCATION
	Any room object can define this function.

SYNTAX
	void exit(object ob);

DESCRIPTION
	This function is called in the old environment every time a
	living object leaves it.  That object is passed to the function
	as an argument.


NOTE
	*** BE EXTREMELY CAREFUL WITH THIS *** A bug in this object can
	mean that anyone entering the room is trapped forever (that is,
	until the next reboot).

	If the object leaves by move_object() or transfer(), then this_player
	will be that object.  But if it leaves by destruct(), then this_player
	will not be the destructed object.  Thus it is better to use the
	argument passed to exit rather than this_player().


SEE ALSO
        init in lfun/basic/init