diff --git a/en_US.ISO8859-1/books/porters-handbook/book.sgml b/en_US.ISO8859-1/books/porters-handbook/book.sgml
index df8de365d4..0085756eaf 100644
--- a/en_US.ISO8859-1/books/porters-handbook/book.sgml
+++ b/en_US.ISO8859-1/books/porters-handbook/book.sgml
@@ -4758,7 +4758,7 @@ PORTVERSION=   1.0</programlisting>
 	    <row>
 	      <entry><makevar>USE_X_PREFIX</makevar></entry>
 
-	      <entry>The port installs in <makevar>X11BASE</makevar>, not
+	      <entry>The port installs in <makevar>X11BASE_REL</makevar>, not
 		<makevar>PREFIX</makevar>.</entry>
 	    </row>
 
@@ -6779,17 +6779,30 @@ as .putsy.conf and edit it.</programlisting>
       </sect1>
 
       <sect1 id="porting-prefix">
-	<title><makevar>PREFIX</makevar></title>
+	<title><makevar>PREFIX</makevar> and <makevar>DESTDIR</makevar></title>
 
-	<para>Do try to make your port install relative to
-	  <makevar>PREFIX</makevar>.  The value of this variable will be set
-	  to <makevar>LOCALBASE</makevar> (default
+	<para><makevar>PREFIX</makevar> determines the location where
+	  the port will install.  It is usually <filename>/usr/local</filename>,
+	  or <filename>/opt</filename>.  User can set <makevar>PREFIX</makevar>
+	  to anything he wants.  Your port must respect this variable.</para>
+
+	<para><makevar>DESTDIR</makevar>, if set by user, determines the
+	  complete alternative environment, usually a jail, or an installed
+	  system mounted elsewhere than <filename>/</filename>.
+	  A port will actually install into
+	  <makevar>DESTDIR</makevar>/<makevar>PREFIX</makevar>, and register
+	  with the package database in <makevar>DESTDIR</makevar>/var/db/pkg.
+	  It is very important to write ports that respect
+	  <makevar>DESTDIR</makevar>.</para>
+
+	<para>The value of <makevar>PREFIX</makevar> will be set
+	  to <makevar>LOCALBASE_REL</makevar> (default
 	  <filename>/usr/local</filename>).  If
 	  <makevar>USE_X_PREFIX</makevar> or <makevar>USE_IMAKE</makevar> is
-	  set, <makevar>PREFIX</makevar> will be <makevar>X11BASE</makevar> (default
+	  set, <makevar>PREFIX</makevar> will be <makevar>X11BASE_REL</makevar> (default
 	  <filename>/usr/X11R6</filename>).  If
 	  <makevar>USE_LINUX_PREFIX</makevar> is set, <makevar>PREFIX</makevar>
-	  will be <makevar>LINUXBASE</makevar> (default
+	  will be <makevar>LINUXBASE_REL</makevar> (default
 	  <filename>/compat/linux</filename>).</para>
 
 	<para>Avoiding the hard-coding of <filename>/usr/local</filename> or
@@ -6840,6 +6853,48 @@ as .putsy.conf and edit it.</programlisting>
 	  <literal>-DPAGER=\"/usr/local/bin/less\"</literal>. This way it will
 	  have a better chance of working if the system administrator has
 	  moved the whole <filename>/usr/local</filename> tree somewhere else.</para>
+
+	<para>Note that <makevar>LOCALBASE</makevar>,
+	  <makevar>LINUXBASE</makevar>, <makevar>X11BASE</makevar>,
+	  <makevar>DOCSDIR</makevar>, <makevar>EXAMPLESDIR</makevar>,
+	  <makevar>DATADIR</makevar>, <makevar>DESKTOPDIR</makevar> variables
+	  already contain <makevar>DESTDIR</makevar>.  Using
+	  <makevar>DESTDIR</makevar>/<makevar>LOCALBASE</makevar> is
+	  wrong.  Use <makevar>LOCALBASE_REL</makevar>,
+	  <makevar>LINUXBASE_REL</makevar>, <makevar>X11BASE_REL</makevar>
+	  if you need a variable relative to <makevar>DESTDIR</makevar>.
+	  To keep things terse, <makevar>TARGETDIR</makevar> can be used to
+	  replace <makevar>DESTDIR</makevar>/<makevar>PREFIX</makevar>.</para>
+
+	<para>Example of correct usage:</para>
+
+	<programlisting>post-install:
+	${INSTALL_PROGRAM} ${WRKSRC}/helper ${TARGETDIR}/bin/helper
+	${INSTALL_DATA} ${WRKSRC}/guide.txt ${DOCSDIR}</programlisting>
+
+	<para>When referencing dependencies in the port, the
+	  <makevar>LOCALBASE</makevar> is used, as we are working with
+	  dependencies inside the target environment.  For hardcoding file
+	  paths in the software, <makevar>LOCALBASE_REL</makevar> must
+	  be used, because the software wil run inside the target
+	  environment.</para>
+
+	<para>Example of correct usage:</para>
+
+	<programlisting>RUN_DEPENDS=	${LOCALBASE}/share/gonzo/launch.dat:${PORTSDIR}/games/gonzo
+
+post-patch:
+	@${REINPLACE_CMD} -e 's|/usr/gonzo/launch.dat|${LOCALBASE_REL}/share/gonzo/launch.dat}' ${WRKSRC}/main.c
+	@${REINPLACE_CMD} -e 's|/etc/game.conf|${PREFIX}/etc/game.conf|' ${WRKSRC}/loader.c
+
+post-install:
+	@${INSTALL_DATA} ${WRKSRC}/example/conf ${TARGETDIR}/etc/game.conf</programlisting>
+
+	<para>In packing lists and in <filename>pkg-*</filename> scripts,
+	  <literal>%%LOCALBASE%%</literal>, <literal>%%LINUXBASE%%</literal>
+	  and <literal>%%X11BASE%%</literal> expansions will contain paths
+	  stripped of <makevar>DESTDIR</makevar>, as all these files are
+	  processed of a context of target environment.</para>
       </sect1>
   </chapter>