diff --git a/en_US.ISO8859-1/books/porters-handbook/special/chapter.xml b/en_US.ISO8859-1/books/porters-handbook/special/chapter.xml
index ab2993f8a8..8b77817d89 100644
--- a/en_US.ISO8859-1/books/porters-handbook/special/chapter.xml
+++ b/en_US.ISO8859-1/books/porters-handbook/special/chapter.xml
@@ -655,6 +655,22 @@ IGNORE=	may not be redistributed because of licensing reasons. Please visit <rep
 		binary.</entry>
 	    </row>
 
+	    <row>
+	      <entry><varname>CMAKE_ON</varname></entry>
+	      <entry>For each entry in <varname>CMAKE_ON</varname>, an
+		enabled boolean value is added to
+		<varname>CMAKE_ARGS</varname>.  See <xref
+		  linkend="using-cmake-example2"/>.</entry>
+	    </row>
+
+	    <row>
+	      <entry><varname>CMAKE_OFF</varname></entry>
+	      <entry>For each entry in <varname>CMAKE_OFF</varname>, a
+		disabled boolean value is added to
+		<varname>CMAKE_ARGS</varname>.  See <xref
+		  linkend="using-cmake-example2"/>.</entry>
+	    </row>
+
 	    <row>
 	      <entry><varname>CMAKE_BUILD_TYPE</varname></entry>
 	      <entry>Type of build (<application>CMake</application>
@@ -760,6 +776,30 @@ IGNORE=	may not be redistributed because of licensing reasons. Please visit <rep
 	<programlisting>USES=			cmake:outsource
 CMAKE_SOURCE_PATH=	&dollar;{WRKSRC}/subproject</programlisting>
       </example>
+
+      <example xml:id="using-cmake-example2">
+	<title><varname>CMAKE_ON</varname> and
+	  <varname>CMAKE_OFF</varname></title>
+
+	<para>When adding boolean values to
+	  <varname>CMAKE_ARGS</varname>, it is easier to use the
+	  <varname>CMAKE_ON</varname> and <varname>CMAKE_OFF</varname>
+	  variables instead.  This:</para>
+
+	<programlisting>CMAKE_ON=	VAR1 VAR2
+CMAKE_OFF=	VAR3</programlisting>
+
+	<para>Is equivalent to:</para>
+
+	<programlisting>CMAKE_ARGS=	-DVAR1:BOOL=TRUE -DVAR2:BOOL=TRUE -DVAR3:BOOL=FALSE</programlisting>
+
+	<important>
+	  <para>This is only for the default values off
+	    <varname>CMAKE_ARGS</varname>.  The helpers described in
+	    <xref linkend="options-cmake_bool"/> use the same
+	    semantics, but for optional values.</para>
+	</important>
+      </example>
     </sect2>
 
     <sect2 xml:id="using-scons">