Add a comment on time.time() returning non-decreasing values except when
the clock is set back.
This closes SF bug #447945.
diff --git a/Doc/lib/libtime.tex b/Doc/lib/libtime.tex
index 6823d5f..83d520e 100644
--- a/Doc/lib/libtime.tex
+++ b/Doc/lib/libtime.tex
@@ -287,7 +287,9 @@
Return the time as a floating point number expressed in seconds since
the epoch, in UTC. Note that even though the time is always returned
as a floating point number, not all systems provide time with a better
-precision than 1 second.
+precision than 1 second. While this function normally returns
+non-decreasing values, it can return a lower value than a previous
+call if the system clock has been set back between the two calls.
\end{funcdesc}
\begin{datadesc}{timezone}