How does Perp Frame choose the local axis of the planes?

Hi!

this question is mainly for david, if he has the time...

I was wondering what's the logic that the Perp Frame component uses when choosing the angles of the frame axis. It would make sense to me for it to choose the X axis as a horizontal one and Y as the highest slope possible, and it seems to do this, but not always, so i am curious which is the algorithm so i can adapt to it.

Have a nice one!