Make a selection. > Hierarchy panel > IK button
The IK rollouts contain controls for interactive IK and the HD IK solver.
Turning on the IK button in the Hierarchy panel displays rollouts that pertain to Interactive IK, Applied IK, and the HD (history-dependent) IK solver.
The HD IK Solver is applied to a hierarchical chain using the Animation > IK menu.
The rollouts for interactive IK are:
Auto Termination Rollout (Interactive IK)
The rollouts for applied IK are:
Object Parameters Rollout (HD Solver)
The rollouts for the HD IK solver are: