Apple Motion 4 - Manual (Page 1198)

3D Transformations in 2D Groups
All objects have 3D transformations available, even when in 2D groups. All can be rotated
around any axis and moved along any axis. Keep in mind that objects in 2D groups are
not depth-sorted, and cannot intersect, regardless of their position in 3D space.
2D parent group in the Layers tab Groups sorted in layer order in Canvas
Both of these groups are positioned at the same point in 3D space, but because they
are layer-ordered, group A does not intersect with group B. If you change the parent
group to 3D, the two groups will intersect.
3D parent group in the Layers tab Groups sorted in depth order in Canvas
Note: If two groups are coplanar (occupy the same plane), they are composited in layer
order, regardless of whether the objects’ parent is a 2D group or 3D group. In a 2D
composite, all objects are coplanar.
1198 Chapter 18 3D Compositing