* doc/lispref/debugging.texi (Error Debugging): Mention debug-on-message.

* etc/NEWS: Related markup.

2 files changed, 10 insertions, 0 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index bc48f74401f..0016258bcb5 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,5 +1,7 @@
 2012-11-11  Glenn Morris  <rgm@gnu.org>
 
+        * debugging.texi (Error Debugging): Mention debug-on-message.
+
         * control.texi (Signaling Errors):
         * debugging.texi (Error Debugging):
         * errors.texi (Standard Errors): Add user-error.
diff --git a/doc/lispref/debugging.texi b/doc/lispref/debugging.texi
index 74000c2ba66..9a43cfeac5d 100644
--- a/doc/lispref/debugging.texi
+++ b/doc/lispref/debugging.texi
@@ -163,6 +163,14 @@ supported values correspond to the signals @code{SIGUSR1} and
 @code{inhibit-quit} is set and Emacs is not otherwise responding.
 @end defopt
 
+@cindex message, finding what causes a particular message
+@defvar debug-on-message
+If you set @code{debug-on-message} to a regular expression,
+Emacs will enter the debugger if it displays a matching message in the
+echo area.  For example, this can be useful when trying to find the
+cause of a particular message.
+@end defvar
+
   To debug an error that happens during loading of the init
 file, use the option @samp{--debug-init}.  This binds
 @code{debug-on-error} to @code{t} while loading the init file, and