Apple Motion 3 - Manual (Page 234)

234 Chapter 2 Creating and Managing Projects
Layers, in turn, are nested within containers known as groups. Whenever you create a
new layer, that layer is placed within a group. You can drag a layer from one group
and place it inside another group, but layers cannot exist on their own, outside of a
group. Layers nested inside groups appear indented in the Layers tab and the
Timeline layers list.
A group can also contain other groups nested inside it. In this way, you can construct
complex hierarchies of nested groups, with each nested group subordinate to the
group that contains it, up to the topmost group.
One of the goals of organizing the layers in a project is to group layers that you want to
work together as a unit. Doing so ensures that animation and effects that are applied
to the enclosing group also affect all layers nested within that group. By nesting related
layers that you want to animate inside a group, you can save time by animating just the
enclosing group, instead of animating each layer individually.
Nested objects
Enclosing group
Nested groups
Enclosing group