sync description for funsubs

mksh.1

@@ -1,8 +1,8 @@
-.\" $MirOS: src/bin/mksh/mksh.1,v 1.302 2013/01/19 17:27:05 tg Exp $
+.\" $MirOS: src/bin/mksh/mksh.1,v 1.303 2013/02/10 23:58:19 tg Exp $
 .\" $OpenBSD: ksh.1,v 1.145 2013/01/17 21:20:25 jmc Exp $
 .\"-
 .\" Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
-.\"		2010, 2011, 2012
+.\"		2010, 2011, 2012, 2013
 .\"	Thorsten Glaser <tg@mirbsd.org>
 .\"
 .\" Provided that these terms and disclaimer and all copyright notices
@@ -74,7 +74,7 @@
 .\" with -mandoc, it might implement .Mx itself, but we want to
 .\" use our own definition. And .Dd must come *first*, always.
 .\"
-.Dd $Mdocdate: January 19 2013 $
+.Dd $Mdocdate: February 10 2013 $
 .\"
 .\" Check which macro package we use, and do other -mdoc setup.
 .\"
@@ -1171,6 +1171,14 @@ and arithmetic substitutions take the form
 Parsing the current-environment command substitution requires a space,
 tab or newline after the opening brace and that the closing brace be
 recognised as a keyword (i.e. is preceded by a newline or semicolon).
+They are also called funsubs (function substitutions) and behave like
+functions in that
+.Ic local
+and
+.Ic return
+work, and in that
+.Ic exit
+terminates the parent shell.
 .Pp
 If a substitution appears outside of double quotes, the results of the
 substitution are generally subject to word or field splitting according to