diff --git a/functions/array.xml b/functions/array.xml
index 992a3b5c8b..21146ef2a4 100644
--- a/functions/array.xml
+++ b/functions/array.xml
@@ -1548,12 +1548,16 @@ function array_values ($arr) {
      </funcprototype>
     </funcsynopsis>
     <simpara>
-     Applies the function named by <parameter>func</parameter> to each
-     element of <parameter>arr</parameter>.
+     Applies the user-defined function named by <parameter>func</parameter> 
+     to each element of <parameter>arr</parameter>.
      <parameter>func</parameter> will be passed array value as the
      first parameter and array key as the second parameter.  If
      <parameter>userdata</parameter> is supplied, it will be passed as
-     the third parameter to the user function.
+     the third parameter to the user function. <parameter>func</parameter> 
+     must be a user-defined function, and can't be a native PHP function.
+     Thus, you can't use <function>array_walk</function> straight with
+     <function>str2lower</function>, you must build a user-defined function
+     with it first, and pass this function as argument.
     </simpara>
     <simpara>
      If <parameter>func</parameter> requires more than two or three