Two new low-level roff(7) features:

* .nr optional third argument (auto-increment step size)
* \n+ and \n- numerical register auto-increment and -decrement
bentley@ reported on Dec 9, 2013 that lang/sbcl(1) uses these.

1 files changed, 17 insertions, 3 deletions

diff --git a/roff.7 b/roff.7
index 2b9053e4..b7f499d9 100644
--- a/roff.7
+++ b/roff.7
@@ -1,7 +1,7 @@
 .\"	$Id$
 .\"
 .\" Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
-.\" Copyright (c) 2010,2011,2013-2015,2017 Ingo Schwarze <schwarze@openbsd.org>
+.\" Copyright (c) 2010-2018 Ingo Schwarze <schwarze@openbsd.org>
 .\"
 .\" Permission to use, copy, modify, and distribute this software for any
 .\" purpose with or without fee is hereby granted, provided that the above
@@ -1348,7 +1348,7 @@ Currently unsupported.
 .It Ic \&nop Ar body
 Execute the rest of the input line as a request or macro line.
 Currently unsupported.
-.It Ic \&nr Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar expression
+.It Ic \&nr Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar expression Op Ar stepsize
 Define or change a register.
 A register is an arbitrary string value that defines some sort of state,
 which influences parsing and/or formatting.
@@ -1360,6 +1360,14 @@ below.
 If it is prefixed by a sign, the register will be
 incremented or decremented instead of assigned to.
 .Pp
+The
+.Ar stepsize
+is used by the
+.Ic \en+
+auto-increment feature.
+It remains unchanged when omitted while changing an existing register,
+and it defaults to 0 when defining a new register.
+.Pp
 The following
 .Ar register
 is handled specially:
@@ -1996,13 +2004,19 @@ and
 Character
 .Ar number
 on the current font.
-.Ss \en Ns Bq Ar name
+.Ss \en Ns Oo +|- Oc Ns Bq Ar name
 Interpolate the number register
 .Ar name .
 For short names, there are variants
 .No \en Ns Ar c
 and
 .No \en( Ns Ar cc .
+If the optional sign is specified,
+the register is first incremented or decremented by the
+.Ar stepsize
+that was specified in the relevant
+.Ic \&nr
+request, and the changed value is interpolated.
 .Ss \eo\(aq Ns Ar string Ns \(aq
 Overstrike, writing all the characters contained in the
 .Ar string