(prefer-coding-system): Fix docstring.

diff --git a/lisp/international/mule-cmds.el b/lisp/international/mule-cmds.el
index fcbf44d934230acbf338620a3716c70ff84c5070..6ff2e46b53a9c3445ffaf0d8058f1ac71b815fe4 100644 (file)
--- a/lisp/international/mule-cmds.el
+++ b/lisp/international/mule-cmds.el
@@ -309,7 +309,10 @@ systems set by this function will use that type of EOL conversion.
 This command does not change the default value of terminal coding system
 for MS-DOS terminal, because DOS terminals only support a single coding
 system, and Emacs automatically sets the default to that coding system at
-startup."
+startup.
+
+Such a coding system that requires automatic detection of text
+encoding (e.g. undecided, unix) can't be preferred."
   (interactive "zPrefer coding system: ")
   (if (not (and coding-system (coding-system-p coding-system)))
       (error "Invalid coding system `%s'" coding-system))