- Add a PLIST_SUB @comment example to the pkg-plist section

svn path=/head/; revision=35085

en_US.ISO8859-1/books/porters-handbook/book.sgml

@@ -8590,6 +8590,25 @@ PLIST_SUB=      OCTAVE_VERSION=${OCTAVE_VERSION}</programlisting>
 	  you will not have to change dozens (or in some cases, hundreds) of
 	  lines in the <filename>pkg-plist</filename>.</para>
 
+	<para>If your port installs files conditionally on the options
+	  set in the port, the usual way of handling it is prefixing
+	  the <filename>pkg-plist</filename> lines with
+	  a <literal>%%TAG%%</literal> and adding that <literal>TAG</literal>
+	  to the <makevar>PLIST_SUB</makevar> variable inside the
+	  <filename>Makefile</filename> with a special value of
+	  <literal>@comment</literal>, which makes package tools to ignore the
+	  line:</para>
+
+	<programlisting>.if defined(WITH_X11)
+PLIST_SUB+=	X11=""
+.else
+PLIST_SUB+=	X11="@comment "
+.endif</programlisting>
+
+	<para>and in the <filename>pkg-plist</filename>:</para>
+
+	<programlisting>%%X11%%bin/foo-gui</programlisting>
+
 	<para>This substitution (as well as addition of any <link
 	  linkend="makefile-manpages">manual pages</link>) will be done between
 	  the <maketarget>pre-install</maketarget> and