From the NannyMUD documentation

LAST CHANGE

2001-08-07

FUNCTION

NAME
        throw - Cause an execution to terminate with an error.


SYNTAX
	void throw(mixed errdata)

DESCRIPTION
	Terminates the execution with an error message. If a prior catch is
	active then execution will resume after the catch statement. In that
	case `errdata' will be returned by the catch statement. Anything can
	be thrown except 0 which is the indicator of no error.


SEE ALSO
        catch in efun/debug/catch