Let you animate the use of constraints. Work with constraint clips on constraint tracks in the Story window.
Use constraint clips to make constraints active for only a segment of a take. For example, you can use a Parent-Child constraint between a cup and a character’s hand. You can create a constraint clip with the Parent-Child constraint to make the constraint active only when the clip plays, so that you can give the impression that the character is actually picking up the cup halfway through the animation.
To create constraint clips:
Dropping the constraint into an empty area of the track list creates a new Constraint track with a constraint clip, and dropping the constraint onto a Constraint track creates a new clip on the track.
To move the Constraint track, click on its name and drag it up or down to the new location in the Action Track list.