diff --git a/en_US.ISO8859-1/books/porters-handbook/book.sgml b/en_US.ISO8859-1/books/porters-handbook/book.sgml
index 96220f284e..227b572ff0 100644
--- a/en_US.ISO8859-1/books/porters-handbook/book.sgml
+++ b/en_US.ISO8859-1/books/porters-handbook/book.sgml
@@ -5032,6 +5032,16 @@ PLIST_SUB+=             NLS="@comment "
 	exist or the distfile does not exist in the directory.  In such case, using author's id as
 	<makevar>MASTER_SITE_SUBDIR</makevar> is allowed.</para>
 
+      <para>All of the tunable knobs below accept both <literal>YES</literal>
+	and a version string, like <literal>5.8.0+</literal>.  Using
+	<literal>YES</literal> means that the port can be used with all
+	of the supported <application>Perl</application> versions.  If a port
+	only works with specific versions of <application>Perl</application>,
+	it can be indicated with a version string, specifying a minimal version
+	(e.g. <literal>5.7.3+</literal>), a maximal version (e.g.
+	<literal>5.8.0-</literal>) or an exact version (e.g.
+	<literal>5.8.3</literal>).</para>
+
       <table frame="none">
 	<title>Variables for ports that use <literal>perl</literal></title>