private function _changedAttribute($attr) 
    {
        preg_match('/(\w+)_(change|changed|was)$/', $attr, $matches);
        if (sizeof($matches) < 1) {
            return null;
        }

        $attr = $matches[1];
        $meth = $matches[2];
        $cur  = $this->get($attr);
        $old  = $this->get($attr, false);

        if ($meth == "was") {
            return $old;
        }
        if ($meth == "changed") {
            return $cur!=$old;
        }
        if ($meth == "change") {
            return array($old, $cur);
        }
        return null;
    }