Index: en_US.ISO8859-1/books/porters-handbook/makefiles/chapter.xml
===================================================================
--- en_US.ISO8859-1/books/porters-handbook/makefiles/chapter.xml
+++ en_US.ISO8859-1/books/porters-handbook/makefiles/chapter.xml
@@ -4390,6 +4390,68 @@
 .endif</programlisting>
       </sect3>
 
+      <sect3 xml:id="options-implies">
+	<title><varname><replaceable>OPT</replaceable>_IMPLIES</varname></title>
+
+	<para>Provides a way to add dependencies between options.</para>
+
+	<para>When <replaceable>OPT</replaceable> is enabled, all the
+	  options listed in this variable will be enabled too.  Using
+	  the <link
+	    linkend="options-configure_enable"><varname><replaceable>OPT</replaceable>_CONFIGURE_ENABLE</varname></link>
+	  described earlier to illustrate:</para>
+
+	<programlisting>OPTIONS_DEFINE=	OPT1 OPT2
+OPT1_IMPLIES=	OPT2
+
+OPT1_CONFIGURE_ENABLE=	opt1
+OPT2_CONFIGURE_ENABLE=	opt2</programlisting>
+
+	<para>Is equivalent to:</para>
+
+	<programlisting>OPTIONS_DEFINE=	OPT1 OPT2
+
+.include &lt;bsd.port.options.mk&gt;
+
+.if ${PORT_OPTIONS:MOPT1}
+CONFIGURE_ARGS+=	--enable-opt1
+.else
+CONFIGURE_ARGS+=	--disable-opt1
+.endif
+
+.if ${PORT_OPTIONS:MOPT2} || ${PORT_OPTIONS:MOPT1}
+CONFIGURE_ARGS+=	--enable-opt2
+.else
+CONFIGURE_ARGS+=	--disable-opt2
+.endif</programlisting>
+      </sect3>
+
+      <sect3 xml:id="options-prevents">
+	<title><varname><replaceable>OPT</replaceable>_PREVENTS</varname></title>
+
+	<para>Provides a way to add conflicts between options.</para>
+
+	<para>When <replaceable>OPT</replaceable> is enabled, all the
+	  options listed in this variable must be disabled.  For example:</para>
+
+	<programlisting>OPTIONS_DEFINE=	OPT1 OPT2
+OPT1_PREVENTS=	OPT2</programlisting>
+
+	<para>Is roughly equivalent to:</para>
+
+	<programlisting>OPTIONS_DEFINE=	OPT1 OPT2
+
+.include &lt;bsd.port.options.mk&gt;
+
+.if ${PORT_OPTIONS:MOPT2} || ${PORT_OPTIONS:MOPT1}
+BROKEN=	Option OPT1 conflicts with OPT2 (select only one)
+.endif</programlisting>
+
+	<para>The only difference is that the first one will write an
+	  error after running <command>make config</command>,
+	  suggesting changing the selected options.</para>
+      </sect3>
+
       <sect3 xml:id="options-dependencies">
 	<title>Dependencies</title>