===================================================================
RCS file: /cvs/mandoc/mandoc.1,v
retrieving revision 1.200
retrieving revision 1.201
diff -u -p -r1.200 -r1.201
--- mandoc/mandoc.1	2017/06/17 22:43:14	1.200
+++ mandoc/mandoc.1	2017/06/17 23:07:00	1.201
@@ -1,4 +1,4 @@
-.\"	$Id: mandoc.1,v 1.200 2017/06/17 22:43:14 schwarze Exp $
+.\"	$Id: mandoc.1,v 1.201 2017/06/17 23:07:00 schwarze Exp $
 .\"
 .\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
 .\" Copyright (c) 2012, 2014-2017 Ingo Schwarze <schwarze@openbsd.org>
@@ -799,6 +799,11 @@ generated by CVS
 or
 .Ic NetBSD
 keyword substitution as conventionally used in these operating systems.
+.It Sy "duplicate RCS id"
+A single manual page contains two copies of the RCS identifier for
+the same operating system.
+Consider deleting the later instance and moving the first one up
+to the top of the page.
 .It Sy "useless macro"
 .Pq mdoc
 A