我的E文太差，自己看看吧
Planted keys have an IK Blend of 1. They are joined to the Previous IK Key and are in Object space, rather than Body space. Planted keys lock the foot or hand to the ground, or to any object.

Sliding keys have moving IK constraints. Sliding footsteps are created if there is a moved IK constraint occurring in the footstep interval. In a footstep animation this means that the foot can be placed anywhere, even though there is a footstep icon. Footstep icons can be thought of as gizmos rather than the absolute location of a foot. Sliding keys have an IK blend of 1, and are in object space, but are not joined to the previous IK key.

Free keys have an IK blend of 0, and are in body space. They are not joined to the previous IK key. Free keys have no IK constraint.

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Now, you'll set a planted key. A planted key will do three things: it will set IK Blend to 1, it will turn on Join to Previous IK Key, and it will turn on Object Space. Together, these three settings ensure that the foot will not go through the ground plane.