public function addStreamFilter(string $filtername, $params = null): self
    {
        if (!$this->document instanceof Stream) {
            throw new Exception('The stream filter API can not be used');
        }

        $this->document->appendFilter($filtername, $this->stream_filter_mode, $params);
        $this->stream_filters[$filtername] = true;
        $this->resetProperties();
        $this->input_bom = null;

        return $this;
    }