Explain in more details how define interacts with pushdef/popdef, and

how that varies from an m4 implementation to another.
ok jmc@

1 files changed, 14 insertions, 1 deletions

diff --git a/usr.bin/m4/m4.1 b/usr.bin/m4/m4.1
index e417d32f39a..6481822022f 100644
--- a/usr.bin/m4/m4.1
+++ b/usr.bin/m4/m4.1
@@ -1,4 +1,4 @@
-.\"	@(#) $OpenBSD: m4.1,v 1.33 2003/06/27 21:22:52 jmc Exp $
+.\"	@(#) $OpenBSD: m4.1,v 1.34 2003/06/29 11:04:03 espie Exp $
 .\"
 .\" Copyright (c) 1989, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -395,6 +395,19 @@ to allow
 .Nm autoconf
 to work.
 .Pp
+The built-ins
+.Ic pushdef
+and
+.Ic popdef
+handle macro definitions as a stack.
+However,
+.Ic define
+interacts with the stack in an undefined way.
+In this implementation,
+.Ic define
+replaces the top-most definition only.
+Other implementations may erase all definitions on the stack instead.
+.Pp
 For portability, one should not use the macros
 .Ic builtin ,
 .Ic esycmd ,