BT81x Custom widget

I am using the Riverdi IoT display with Zerynth. I want to implement widgets on this display, but Bt81x library has few widgets like spinners widget. But I am looking for more widgets. By reading the documentation you guys have stated that " bt81x library support external QSPI NOR flash to fetch graphic elements (image, font, widget, etc)". What does it mean? how can I achieve that? Thanks