public function start() {

        // indicate the library that it should execute queued requests
        $this->_queue = false;

        // if we have to pause between batches of requests, process them sequentially, in batches
        if ($this->pause_interval > 0) $this->_process_paused();

        // if we don't have to pause between batches of requests, process them all at once
        else $this->_process();

    }