Use semantic markup.

lib/libc/stdio/setbuf.3

@@ -1,4 +1,4 @@
-.\"	$NetBSD: setbuf.3,v 1.16 2018/02/20 09:36:26 wiz Exp $
+.\"	$NetBSD: setbuf.3,v 1.17 2018/02/20 17:16:51 uwe Exp $
 .\"
 .\" Copyright (c) 1980, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -65,12 +65,12 @@ output or input is read from any stream attached to a terminal device
 (typically stdin).
 .Pp
 The default buffer settings can be overwritten per descriptor
-.Dv ( STDBUFn )
+.Ev ( STDBUF Ns Ar n )
 where
-.Dv n
+.Ar n
 is the numeric value of the file descriptor represented by the stream, or
 for all descriptors
-.Dv ( STDBUF ) .
+.Ev ( STDBUF ) .
 The environment variable value is a letter followed by an optional numeric
 value indicating the size of the buffer.
 Valid sizes range from 0B to 1MB.
@@ -97,10 +97,10 @@ is called,
 and an optimally-sized buffer is obtained.
 If a stream refers to a terminal
 (as
-.Em stdout
+.Va stdout
 normally does) it is line buffered.
 The standard error stream
-.Em stderr
+.Va stderr
 is initially unbuffered.
 .Pp
 The