oh true. So there will also be another type of boundary which has a direction associated. And a sorta don't know area when you are mid fall with some limited ma

oh true. So there will also be another type of boundary which has a direction associated. And a sorta don't know area when you are mid fall with some limited manoeuvrability (non-holonomic movement). Best not to try and categorise the non-holonomic areas in too much detail as that's a rabbit hole.