Random spawning questions

I'm trying to override some of the ways minecraft spawns things in by replacing and adding mobs using conditions and random spawning options. I have some questions about things I can't seem to get working.

First, I'm given to understand through some recent posts on the matter that the ADD action does not work with biomes at all. Is this intentional or a bug that will eventually be fixed?

Second, can someone explain to me the "PointsPerSecond" config.yml lines? What constitutes Land, Air,...

Random spawning questions