extsep description:

- avoid "e.g." in text
- record version information
(should be backported)

Doc/lib/libos.tex

@@ -1644,8 +1644,9 @@ backslash.
 \end{datadesc}
 
 \begin{datadesc}{extsep}
-The character which separates the base filename from the extension,
-e.g. \character{.} in \code{os.py}.
+The character which separates the base filename from the extension;
+for example, the \character{.} in \file{os.py}.
+\versionadded{2.2}
 \end{datadesc}
 
 \begin{datadesc}{pathsep}