I would like to comment on the following post:

A note of caution: function_exists() appears to be case-insensitive (at least as of PHP 4.3.8).  e.g.:

<?php
   function MyCasedFunction() {
       return true;
   }

   // Will return true, even though casing is "wrong"
   if (function_exists("mYcAsEdFuNcTiOn"))
       echo "I see it!";
?> 

I believe that function calls itself are case insensitve, so this function is returning a valid truth. PHP doesn't care about cases.