M-s is only available in Text mode and its submodes.

diff --git a/man/text.texi b/man/text.texi
index 08b9e625b3c7eac806ae374e0c8af0520dc0641b..bf68558d869e827543dadbb73e8e5635d0de2832 100644 (file)
--- a/man/text.texi
+++ b/man/text.texi
@@ -532,7 +532,9 @@ see @ref{Format Justification}.
 @findex center-line
   The command @kbd{M-s} (@code{center-line}) centers the current line
 within the current fill column.  With an argument @var{n}, it centers
-@var{n} lines individually and moves past them.
+@var{n} lines individually and moves past them.  This binding is
+made by Text mode and is available only in that and related modes
+(@pxref{Text Mode}).
 
 @vindex fill-column
 @kindex C-x f