Mute / solo per group in the Keyframe Editor - layer animations along the
rig, for example animating only the lower body of a walk on a humanoid. This
set the path for the additive and override layers that arrived later.
Pinned IK points - pin an IK point to where it currently stands, so the
feet of a walk cycle stay on the floor. Pinning to a transform, such as a
weapon prefab in the live scene, was planned from here.