warn about bacslash-s lacking
diff --git a/Doc/libregex.tex b/Doc/libregex.tex
index 1b18679..4c98e59 100644
--- a/Doc/libregex.tex
+++ b/Doc/libregex.tex
@@ -4,9 +4,12 @@
This module provides regular expression matching operations similar to
those found in Emacs. It is always available.
-By default the patterns are Emacs-style regular expressions; there is
+By default the patterns are Emacs-style regular expressions,
+with one exception. There is
a way to change the syntax to match that of several well-known
-\UNIX{} utilities.
+\UNIX{} utilities. The exception is that Emacs' \samp{\e s}
+pattern is not supported, since the original implementation references
+the Emacs syntax tables.
This module is 8-bit clean: both patterns and strings may contain null
bytes and characters whose high bit is set.