private function write_log()
    {
        $log_output_file = $this->getOptions()->getLogOutputFile();
        if (!$log_output_file || !is_writable($log_output_file)) {
            return;
        }

        $frames = Frame::$ID_COUNTER;
        $memory = memory_get_peak_usage(true) / 1024;
        $time = (microtime(true) - $this->startTime) * 1000;

        $out = sprintf(
            "<span style='color: #000' title='Frames'>%6d</span>" .
            "<span style='color: #009' title='Memory'>%10.2f KB</span>" .
            "<span style='color: #900' title='Time'>%10.2f ms</span>" .
            "<span  title='Quirksmode'>  " .
            ($this->quirksmode ? "<span style='color: #d00'> ON</span>" : "<span style='color: #0d0'>OFF</span>") .
            "</span><br />", $frames, $memory, $time);

        $out .= ob_get_contents();
        ob_clean();

        file_put_contents($log_output_file, $out);
    }