Multi select filtering is when you have multiple filter buttons active at the same time.
In the free version you only have one filter button active at a time. But with the premium version it’s possible to have multiple buttons active. The filter categories of the buttons are then added together.
That means you can have multiple buttons:
If you now click on the cats button, only the cats show. If you afterwards click on the dogs button, you see cats and dogs. Both buttons are active. To remove the cats, click on the cats button again.
To use the multi select filtering feature, add the df-multi class to your df-area section.