(PHP 5 >= 5.2.0)
mb_strripos — Finds position of last occurrence of a string within another, case insensitive
$haystack
   , string $needle
   [, int $offset = 0
   [, string $encoding = mb_internal_encoding()
  ]] )
   mb_strripos() performs multi-byte safe
   strripos() operation based on
   number of characters. needle position is
   counted from the beginning of
   haystack. First character's position is
   0. Second character position is 1. 
   Unlike mb_strrpos(),
   mb_strripos() is case-insensitive.
  
haystack
       The string from which to get the position of the last occurrence
       of needle
      
needle
       The string to find in haystack
      
offset
       The position in haystack
       to start searching
      
encodingCharacter encoding name to use. If it is omitted, internal character encoding is used.
   Return the numeric position of
   the last occurrence of needle in the
   haystack string, or FALSE
   if needle is not found.