Add notes to __builtin__.float() and string.atof() that the NaN and Inf
results are possible but non-portable.
diff --git a/Doc/lib/libstring.tex b/Doc/lib/libstring.tex
index 56dcf6d..a83d821 100644
--- a/Doc/lib/libstring.tex
+++ b/Doc/lib/libstring.tex
@@ -59,11 +59,15 @@
\begin{funcdesc}{atof}{s}
Convert a string to a floating point number. The string must have
the standard syntax for a floating point literal in Python,
- optionally preceded by a sign (\samp{+} or \samp{-}), or be
- \code{'NaN'} (case insensitive) to indicate the IEEE ``Not a
- Number'' value. Note that this behaves identical to the built-in
- function \function{float()}\bifuncindex{float} when passed a
- string.
+ optionally preceded by a sign (\samp{+} or \samp{-}). Note that
+ this behaves identical to the built-in function
+ \function{float()}\bifuncindex{float} when passed a string.
+
+ \strong{Note:} When passing in a string, values for NaN\index{NaN}
+ and Infinity\index{Infinity} may be returned, depending on the
+ underlying C library. The specific set of strings accepted which
+ cause these values to be returned depends entirely on the C library
+ and is known to vary.
\end{funcdesc}
\begin{funcdesc}{atoi}{s\optional{, base}}