diff --git a/functions/strings.xml b/functions/strings.xml
index 5c4911941c..a578c963ae 100644
--- a/functions/strings.xml
+++ b/functions/strings.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.138 $ -->
+<!-- $Revision: 1.139 $ -->
  <reference id="ref.strings">
   <title>String functions</title>
   <titleabbrev>Strings</titleabbrev>
@@ -1871,6 +1871,30 @@ END;
    </refsect1>
   </refentry>
 
+  <refentry id='function.str-rot13'>
+   <refnamediv>
+    <refname>str_rot13</refname>
+    <refpurpose>Perform the rot13 transform on a string</refpurpose>
+   </refnamediv>
+   <refsect1>
+    <title>Description</title>
+    <funcsynopsis>
+     <funcprototype>
+      <funcdef>string <function>str_rot13</function></funcdef>
+      <paramdef>string <parameter>str</parameter></paramdef>
+     </funcprototype>
+    </funcsynopsis>
+    <para>
+     This function performs the ROT13 encoding on the
+     <parameter>str</parameter> argument and returns the resulting
+     string. The ROT13 encoding simply shifts every letter by 13
+     places in the alphabet while leaving non-alpha characters
+     untouched. Encoding and decoding are done by the same function,
+     passing an encoded string as argument will return the original version.
+    </para>
+   </refsect1>
+  </refentry>
+
   <!-- this section is nearly-identical to trim, ltrim and rtrim -->
   <refentry id="function.rtrim">
    <refnamediv>