"system-name" variable undefined, yet Info suggests it should be defined

[Alan]

Info node "(lispref)System Environment" says:

-- Function: system-name
This function returns the name of the machine you are running on.
(system-name)
=> "prep.ai.mit.edu"

The symbol `system-name' is a variable as well as a function. In
fact, the function returns whatever value the variable `system-name'
currently holds. Thus, you can set the variable `system-name' in case
Emacs is confused about the name of your system.

-----------------------------------------------------------------

I am running

XEmacs 21.4 (patch 21) "Educational Television" [Lucid] (i586-pc-
win32) of Sun Oct 07 2007 on VSHELTON-PC2

In this case variable "system-name" is undefined, yet function "system-
name" does tell me the name of the system.