In an old feature post I found this:
I noticed that the knockout continued into the filled shape. But I don’t understand how they did it. It looks like this for me:
Now I’m left wondering if the post used a polygon that filled around the knockout area, of if there is a trick I’m unaware of.
I might have answered my own question just now, but it is possible to use a pour to achieve the wanted result:
The only thing I dislike about this is the corner smoothing:
The corner smoothing is affected by the “Minimum width” parameter in the Copper Zone properties. The smaller, the smoother.
I suspected something like this. However, this is a silkscreen-zone, so there are no properties
oh wow, I’ve seem to be absolutely blind. Thank you 
I know that kind of blindness. Happy to help.
