An optional array containing the sub-cells of this cell.
- iOS 5.0+
- macOS 10.6+
- Mac Catalyst 13.0+
- tvOS 9.0+
- Core Animation
When specified, each particle emitted by the cell acts as an emitter for each of the cell's sub-cells. The emission point is the current particle position and the emission angle is relative to the current direction of the particle.
The default value of this property is