To better match groff parsing, reject digits and some mathematical

[mandoc.git] / roff.7

diff --git a/roff.7 b/roff.7
index 6ca3029d738ca3cdd3905d30f7342c6778da6f51..2d58efd6cec3c9ef67e9e515102698eddb7935b9 100644 (file)
--- a/roff.7
+++ b/roff.7
@@ -1,4 +1,4 @@
-.\" $Id: roff.7,v 1.117 2022/05/20 13:09:13 schwarze Exp $
+.\" $Id: roff.7,v 1.120 2022/05/31 20:23:05 schwarze Exp $
 .\"
 .\" Copyright (c) 2010-2019, 2022 Ingo Schwarze <schwarze@openbsd.org>
 .\" Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
@@ -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: May 20 2022 $
+.Dd $Mdocdate: May 31 2022 $
 .Dt ROFF 7
 .Os
 .Sh NAME
@@ -2021,8 +2021,23 @@ End conditional input; see
 Paddable non-breaking space character.
 .It Ic \e0
 Digit width space character.
-.It Ic \eA\(aq Ns Ar string Ns Ic \(aq
-Anchor definition; ignored by
+.It Ic \eA\(aq Ns Ar name Ns Ic \(aq
+Interpolate
+.Sq 1
+if
+.Ar name
+is a syntactically valid identifier that can be used
+as a name for a macro or user-defined string, or
+.Sq 0
+otherwise.
+This is a thoroughly non-portable groff extension.
+Heirloom troff uses the same escape sequence with the same syntax
+for a completely different purpose,
+defining a hyperlink target position, also called an
+.Dq anchor ,
+with the given
+.Ar name .
+The Heirloom semantics is not supported by
 .Xr mandoc 1 .
 .It Ic \ea
 Leader character; ignored by
@@ -2085,7 +2100,8 @@ defaults to
 .Ic \efP .
 .It Ic \eg[ Ns Ar name Ns Ic \&]
 Interpolate the format of a number register; ignored by
-.Xr mandoc 1 .
+.Xr mandoc 1 ,
+which interpolates an empty string instead.
 For short names, there are variants
 .Ic \eg Ns Ar c
 and
@@ -2188,12 +2204,16 @@ Horizontal tab; ignored by
 Move up by half a line; ignored by
 .Xr mandoc 1 .
 .It Ic \eV[ Ns Ar name Ns Ic \&]
-Interpolate an environment variable; ignored by
-.Xr mandoc 1 .
+Interpolate an environment variable.
 For short names, there are variants
 .Ic \eV Ns Ar c
 and
 .Ic \eV( Ns Ar cc .
+This escape sequence is intentionally unsupported;
+.Xr mandoc 1
+prints the string
+.Dq Pf $ Brq Ar name
+instead of inspecting the environment.
 .It Ic \ev\(aq Ns Ar number Ns Ic \(aq
 Vertical motion; ignored by
 .Xr mandoc 1 .