From the NannyMUD documentation

LAST CHANGE

2001-09-29

FUNCTION

NAME
        is_mortal - Is the object a mortal?


LOCATION
        This function is located in /obj/player.

AVAILABILITY
        This function can be called by any object.

SYNTAX
        nomask int is_mortal()

DESCRIPTION
	This function asserts that the object in which it exists fully
	qualifies as a mortal. It is mainly used internally in the
	player object, but is available to other objects for
	convenience.


NOTE
	The lib does NOT use this function to perform security checks.