A plane at the far side of the loaded models along a world axis, its normal along it, so a drag moves it back through them; null without a model
A plane through coordinate with normal (render space mm)
A horizontal plane at the top of the loaded models, where the "Top" section plane starts; null without a model
A plane at the far side of the loaded models along a world axis, its normal along it, so a drag moves it back through them; null without a model