Apple Motion 4 - Manual (Page 726)

The following images show masks applied to the source layer of a replicator.
Mask applied to the
replicator cell source
layer
When a masked layer is used as the source for a replicator cell, the mask is respected in
the elements that appear onscreen.
Original source Circle mask applied to source Masked layer used as
replicator source
Masks can also be applied to the replicator layer.
Mask applied to
replicator
When the mask is applied to a replicator, the entire pattern onscreen becomes masked.
Circle mask applied to the
replicator
726 Chapter 12 Using the Replicator