perform symbol function indirection explicitly.
@c Emacs 19 feature
-@defun indirect-function function
+@defun indirect-function function &optional noerror
@anchor{Definition of indirect-function}
This function returns the meaning of @var{function} as a function. If
@var{function} is a symbol, then it finds @var{function}'s function
definition and starts over with that value. If @var{function} is not a
symbol, then it returns @var{function} itself.
-This function signals a @code{void-function} error if the final
-symbol is unbound and a @code{cyclic-function-indirection} error if
-there is a loop in the chain of symbols.
+This function signals a @code{void-function} error if the final symbol
+is unbound and optional argument @var{noerror} is @code{nil} or
+omitted. Otherwise, if @var{noerror} is non-@code{nil}, it returns
+@code{nil} if the final symbol is unbound.
+
+It signals a @code{cyclic-function-indirection} error if there is a
+loop in the chain of symbols.
Here is how you could define @code{indirect-function} in Lisp: