text: I've updated the area, so that grass areas aren't covered by others, but to be honest, I'm also not sure if that's what AlbertCohen has meant, especially since this change takes 2 minutes and this note has been discussed for months now.
  
  As for "You could also argue that every area ( building, parking, etc. ) located in residential area has to be cuted out": No, because residential areas actually describe a landUSE and buildings are part of this area whereas  landuse=grass de facto only means landcover (which as far as I know isn't rendered anywhere) and is only used to paint the map green.
  
  see: https://wiki.openstreetmap.org/wiki/Landcover