Add as simple as possible explanation for Popup, because I still see people adding it as a widget and then wondering why it "doesn't work". This is also a good link for beginners to get to know Factory (kind of forces them to), which makes stuff way simpler in the future.

I'm not sure if I should add it to the ModalView too, as I haven't seen the same issue with it yet, which means that ModalView either isn't used as the first option, or people just don't have the feeling to add that widget as a child somewhere (although there's only a little difference between them).