correct inaccurate and misplaced information in CAVEATS

and move it in part to the DESCRIPTION, in part to STANDARDS;
triggered by a loosely related bug report from Lars dot Nooden at gmail dot com;
OK jmc@, and no opposition when shown on bugs@

usr.bin/sed/sed.1

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: sed.1,v 1.57 2018/11/14 10:59:33 martijn Exp $
+.\"	$OpenBSD: sed.1,v 1.58 2018/12/10 17:12:24 schwarze Exp $
 .\"
 .\" Copyright (c) 1992, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -32,7 +32,7 @@
 .\"
 .\"	from: @(#)sed.1	8.2 (Berkeley) 12/30/93
 .\"
-.Dd $Mdocdate: November 14 2018 $
+.Dd $Mdocdate: December 10 2018 $
 .Dt SED 1
 .Os
 .Sh NAME
@@ -277,6 +277,20 @@ functions all accept additional arguments.
 The synopses below indicate which arguments have to be separated from
 the function letters by whitespace characters.
 .Pp
+The
+.Ic a ,
+.Ic c ,
+.Ic i ,
+.Ic r ,
+and
+.Ic w
+functions cannot be followed by another command separated with a semicolon.
+The
+.Ar text
+and
+.Ar file
+arguments may contain semicolon characters.
+.Pp
 Functions can be combined to form a
 .Em function list ,
 a list of
@@ -561,6 +575,14 @@ The flags
 .Op Fl aEiru
 are extensions to that specification.
 .Pp
+Following the
+.Ic b ,
+.Ic t ,
+or
+.Ic \&:
+commands with a semicolon and another command is an extension to the
+specification.
+.Pp
 The use of newlines to separate multiple commands on the command line
 is non-portable;
 the use of newlines to separate multiple commands within a command file
@@ -571,11 +593,3 @@ A
 .Nm
 command appeared in
 .At v7 .
-.Sh CAVEATS
-The use of semicolons to separate multiple commands
-is not permitted for the following commands:
-.Ic a , b , c ,
-.Ic i , r , t ,
-.Ic w , \&: ,
-and
-.Ic # .