Document filter.
diff --git a/Doc/lib/libfnmatch.tex b/Doc/lib/libfnmatch.tex
index 4d184bc..888580a6 100644
--- a/Doc/lib/libfnmatch.tex
+++ b/Doc/lib/libfnmatch.tex
@@ -43,6 +43,11 @@
false; the comparison is case-sensitive.
\end{funcdesc}
+\begin{funcdesc}{filter}{names, pattern}
+Return the subset of the list of \var{names} that match \var{pattern}.
+It is the same as \code{[n for n in names if fnmatch(n, pattern)]}, but
+implemented more efficiently.
+\end{funcdesc}
\begin{seealso}
\seemodule{glob}{\UNIX{} shell-style path expansion.}