Minor markup adjustments.
diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index fa9f0f3..bc935b2 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -300,8 +300,8 @@
Availability: Macintosh, \UNIX, Windows.
\versionchanged[When specified, the \var{mode} argument must now start
- with one of the letters \code{'r'}, \code{'w'}, or \code{'a'},
- otherwise a \exception{ValueError} is raised. ]{2.3}
+ with one of the letters \character{r}, \character{w}, or \character{a},
+ otherwise a \exception{ValueError} is raised]{2.3}
\end{funcdesc}
\begin{funcdesc}{popen}{command\optional{, mode\optional{, bufsize}}}