Added note about xmon.

etc/ChangeLog

+2003-01-27  Jan Dj,Ad(Brv  <jan.h.d@swipnet.se>
+
+	* DEBUG: Added note about xmon.
+
 2003-01-20  Joanna Pluta  <joanna_p@gazeta.pl>
 
 	* TUTORIAL.pl: Updated.

etc/DEBUG

@@ -305,6 +305,19 @@ procedure:
   - You should now look around this offending X call and try to figure
     out what is wrong with it.
 
+** If Emacs causes errors or memory leaks in your X server
+
+You can trace the traffic between Emacs and your X server with a tool
+like xmon, available at ftp://ftp.x.org/contrib/devel_tools/.
+
+Xmon can be used to see exactly what Emacs sends when X protocol errors
+happen.  If Emacs causes the X server memory usage to increase you can
+use xmon to see what items Emacs creates in the server (windows,
+graphical contexts, pixmaps) and what items Emacs delete.  If there
+are consistently more creations than deletions, the type of item
+and the activity you do when the items get created can give a hint where
+to start debugging.
+
 ** If the symptom of the bug is that Emacs fails to respond
 
 Don't assume Emacs is `hung'--it may instead be in an infinite loop.