- Add a note about OPTIONS_SUB.

- Add a warning about the *_TARGET options helpers.

Discussed with:	bjk
Sponsored by:	Absolight

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

@@ -3691,6 +3691,13 @@ PLIST_SUB+=	OPT1="" NO_OPT1="@comment "
 .else
 PLIST_SUB+=	OPT1="@comment " NO_OPT1=""
 .endif</programlisting>
+
+	<note>
+	  <para>The value of <varname>OPTIONS_SUB</varname> is
+	    ignored.  Setting it to any value will add
+	    <varname>PLIST_SUB</varname> entries for
+	    <emphasis>all</emphasis> options.</para>
+	</note>
       </sect3>
 
       <sect3 xml:id="options-configure_enable">
@@ -4027,6 +4034,36 @@ LIB_DEPENDS+=	liba.so:${PORTSDIR}/devel/a
 	  </listitem>
 	</itemizedlist>
 
+	<warning>
+	  <para>Some of these variables, at least
+	    <varname>ALL_TARGET</varname> and
+	    <varname>INSTALL_TARGET</varname>, have their default
+	    values set <emphasis>after</emphasis> the options are
+	    processed.</para>
+	  
+	  <para>With the following lines in the
+	    <filename>Makefile</filename>:</para>
+
+	  <programlisting>ALL_TARGET=	all
+
+DOCS_ALL_TARGET=	doc</programlisting>
+
+	  <para>If the <literal>DOCS</literal> option is enabled,
+	    <varname>ALL_TARGET</varname> will have a final value of
+	    <literal>all doc</literal>; if the option is disabled, it
+	    would have a value of <literal>all</literal>.</para>
+
+	  <para>With only the options helper line in the
+	    <filename>Makefile</filename>:</para>
+
+	  <programlisting>DOCS_ALL_TARGET=	doc</programlisting>
+	  
+	  <para>If the <literal>DOCS</literal> option is enabled,
+	    <varname>ALL_TARGET</varname> will have a final value of
+	    <literal>doc</literal>; if the option is disabled, it
+	    would have a value of <literal>all</literal>.</para>
+	</warning>
+
 	<sect4>
 	  <title><varname><replaceable>X</replaceable>_<replaceable>ABOVEVARIABLE</replaceable></varname></title>