===================================================================
RCS file: /cvs/mandoc/eqn.7,v
retrieving revision 1.20
retrieving revision 1.21
diff -u -p -r1.20 -r1.21
--- mandoc/eqn.7	2011/07/23 12:01:54	1.20
+++ mandoc/eqn.7	2011/07/23 12:08:43	1.21
@@ -1,4 +1,4 @@
-.\"	$Id: eqn.7,v 1.20 2011/07/23 12:01:54 kristaps Exp $
+.\"	$Id: eqn.7,v 1.21 2011/07/23 12:08:43 kristaps Exp $
 .\"
 .\" Copyright (c) 2011 Kristaps Dzonsons <kristaps@bsd.lv>
 .\"
@@ -203,6 +203,22 @@ In mandoc, this is interpreted as a comment.
 In troff, The circumflex and tilde white-space symbols map to
 fixed-width spaces.
 In mandoc, these characters are synonyms for the space character.
+.It
+The troff implementation of
+.Nm
+allows for equation alignment with the
+.Cm mark
+and
+.Cm lineup
+tokens.
+mandoc discards these tokens.
+The
+.Cm back Ar n ,
+.Cm fwd Ar n ,
+.Cm up Ar n ,
+and
+.Cm down Ar n
+commands are also ignored.
 .El
 .Sh SEE ALSO
 .Xr mandoc 1 ,