Index: en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml
===================================================================
--- en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml
+++ en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml
@@ -450,6 +450,48 @@
       <programlisting>USES=	dos2unix
 DOS2UNIX_WRKSRC=	${WRKDIR}</programlisting>
     </sect2>
+
+    <sect2 xml:id="slow-patch-extra">
+      <title>Patching Conditionnally.</title>
+
+      <para>From time to time, a port will need patches that should
+	only be applied for specific &os; versions, or depending
+	whether an option is enabled or not.  To apply patches
+	conditionnally, add the full path to their files to
+	<varname>EXTRA_PATCHES</varname>.</para>
+
+      <example xml:id="slow-patch-extra-ex1">
+	<title>Applying a Patch for a Specific &os; Version.</title>
+
+	<programlisting>.include &lt;bsd.port.options.mk&gt;
+
+.if ${OPSYS} == FreeBSD &amp;&amp; ${OSVERSION} &lt; 1100062
+EXTRA_PATCHES=	${PATCHDIR}/extra-patch-fbsd10
+.endif
+
+.include &lt;bsd.port.mk&gt;</programlisting>
+
+      </example>
+
+      <example xml:id="slow-patch-extra-ex2">
+	<title>Optionnaly Applying a Patch.</title>
+
+	<para>When an <link linkend="makefile-options">option</link>
+	  requires a patch, use
+	  <varname><replaceable>opt</replaceable>_EXTRA_PATCHES</varname>
+	  and
+	  <varname><replaceable>opt</replaceable>_EXTRA_PATCHES_OFF</varname>.
+	  See <xref linkend="options-variables"/> for more
+	  information.</para>
+
+	<programlisting>OPTIONS_DEFINE=	  FOO BAR
+FOO_EXTRA_PATCHES=  ${PATCHDIR}/extra-patch-foo
+BAR_EXTRA_PATCHES_OFF=	${PATCHDIR}/extra-patch-bar.c \
+		${PATCHDIR}/extra-patch-bar.h</programlisting>
+
+      </example>
+
+    </sect2>
   </sect1>
 
   <sect1 xml:id="slow-configure">