Add a tip on how to sort targets when options helpers are used.

Sponsored by:	Absolight

en_US.ISO8859-1/books/porters-handbook/order/chapter.xml

@@ -523,5 +523,26 @@ post-install-EXAMPLES-on:
 	<para><varname>test</varname></para>
       </listitem>
     </itemizedlist>
+
+    <tip>
+      <para>When using options helpers target keep them alphabetically
+	sorted, but keep the
+	<literal><replaceable>*</replaceable>-on</literal> before the
+	<literal><replaceable>*</replaceable>-off</literal>.  When
+	also using the main target, keep the main target before the
+	optionnal ones:</para>
+
+      <programlisting>post-install:
+	# install generic bits
+
+post-install-DOCS-on:
+	# Install documentation
+
+post-install-X11-on:
+	# Install X11 related bits
+
+post-install-X11-off:
+	# Install bits that should be there if X11 is disabled</programlisting>
+    </tip>
   </sect1>
 </chapter>