added warning about incompatibility with other codes' use of sys.exitfunc.
diff --git a/Doc/lib/libatexit.tex b/Doc/lib/libatexit.tex
index df0cdd4..e74cc74 100644
--- a/Doc/lib/libatexit.tex
+++ b/Doc/lib/libatexit.tex
@@ -20,6 +20,14 @@
\code{sys.exitfunc} variable.
\withsubitem{(in sys)}{\ttindex{exitfunc}}
+Note: This module is unlikely to work correctly when used with other code
+that sets \code{sys.exitfunc}. In particular, other core Python modules are
+free to use \module{atexit} without the programmer's knowledge. Authors who
+use \code{sys.exitfunc} should convert their code to use
+\module{atexit} instead. The simplest way to convert code that sets
+\code{sys.exitfunc} is to import \module{atexit} and register the function
+that had been bound to \code{sys.exitfunc}.
+
\begin{funcdesc}{register}{func\optional{, *args\optional{, **kargs}}}
Register \var{func} as a function to be executed at termination. Any
optional arguments that are to be passed to \var{func} must be passed