===================================================================
RCS file: /cvs/mandoc/roff.7,v
retrieving revision 1.83
retrieving revision 1.85
diff -u -p -r1.83 -r1.85
--- mandoc/roff.7	2017/06/04 00:13:15	1.83
+++ mandoc/roff.7	2017/06/06 15:03:35	1.85
@@ -1,4 +1,4 @@
-.\"	$Id: roff.7,v 1.83 2017/06/04 00:13:15 schwarze Exp $
+.\"	$Id: roff.7,v 1.85 2017/06/06 15:03:35 schwarze Exp $
 .\"
 .\" Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
 .\" Copyright (c) 2010,2011,2013-2015,2017 Ingo Schwarze <schwarze@openbsd.org>
@@ -15,7 +15,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: June 4 2017 $
+.Dd $Mdocdate: June 6 2017 $
 .Dt ROFF 7
 .Os
 .Sh NAME
@@ -527,7 +527,10 @@ Trailing characters are ignored.
 Center the next
 .Ar N
 input lines without filling.
-Currently ignored.
+.Ar N
+defaults to 1.
+An argument of 0 or less ends centering.
+Currently, high level macros abort certering.
 .It Ic \&cf Ar filename
 Output the contents of a file.
 Ignored because insecure.
@@ -1296,7 +1299,9 @@ Set title line length.
 Currently ignored.
 .It Ic \&mc Ar glyph Op Ar dist
 Print margin character in the right margin.
-Currently ignored.
+The
+.Ar dist
+is currently ignored; instead, 1n is used.
 .It Ic \&mediasize Ar media
 Set the device media size.
 This is a Heirloom extension and currently ignored.