Set Driven Key-Constraint blending
You can constrain and place set driven keys on the same channels of an object.
When set driven keys and constraints are applied to the same object, and they both affect the same channels (such as a point constraint and set driven keys on Translate channels), a pairBlend node is automatically generated as a link or intermediary between the constraints, set driven key animation channels, and the object to which both are applied. When an object is driven by multiple constraints and set driven keys, a separate pairBlend node is created for each group of related influences. For example, a pairBlend node is created for an orient constraint and set driven keys on Rotate channels, as well as for a scale constraint and set driven keys on Scale channels.
Once the set driven key animation channels and constraints are linked to the pairBlend node, you can then modify and animate the weight of the Set Driven Key-Constraint blend to generate various effects. For example, you can control the movement of a collarbone as its neighboring arm moves up and down by blending between the set driven key controlling the collar bone’s rotation and the constraint that directly rotates the collarbone.