public function addUserAgentHandler(WURFL_Handlers_Handler $handler)
    {
        $size = count($this->_userAgentHandlers);
        if ($size > 0) {
            $this->_userAgentHandlers[$size-1]->setNextHandler($handler);
        }
        $this->_userAgentHandlers[] = $handler;
        return $this;
    }