indicate that 'b' is added to the mode flag if not given
diff --git a/Doc/lib/libgzip.tex b/Doc/lib/libgzip.tex
index aab70a1..7a526b6 100644
--- a/Doc/lib/libgzip.tex
+++ b/Doc/lib/libgzip.tex
@@ -41,8 +41,8 @@
\code{'a'}, \code{'ab'}, \code{'w'}, or \code{'wb'}, depending on
whether the file will be read or written. The default is the mode of
\var{fileobj} if discernible; otherwise, the default is \code{'rb'}.
-Be aware that only the \code{'rb'}, \code{'ab'}, and \code{'wb'}
-values should be used for cross-platform portability.
+If not given, the 'b' flag will be added to the mode to ensure the
+file is opened in binary mode for cross-platform portability.
The \var{compresslevel} argument is an integer from \code{1} to
\code{9} controlling the level of compression; \code{1} is fastest and