if you want to get the position of a substring relative to a substring of your string, BUT in REVERSE way:

<?php

function strpos_reverse_way($string,$charToFind,$relativeChar) {
    //
    $relativePos = strpos($string,$relativeChar);
    $searchPos = $relativePos;
    $searchChar = '';
    //
    while ($searchChar != $charToFind) {
        $newPos = $searchPos-1;
        $searchChar = substr($string,$newPos,strlen($charToFind));
        $searchPos = $newPos;
    }
    //
    if (!empty($searchChar)) {
        //
        return $searchPos;
        return TRUE;
    }
    else {
        return FALSE;
    }
    //
}

?>