To take advantage of this feature, you must have a mesh with
relative shape keys and shape Ipo curves with drivers referring
to bones of the mesh's parent armature.
The BGE will automatically detect the dependency between the
shape keys and the armature and execute the Ipo drivers during
the rendering of the armature actions.
This technique is used to make the armature action more natural:
the shape keys compensate in places where the armature deformation
is uggly and the drivers make sure that the shape correction
is synchronized with the bone position.
Note: This is not compatible with shape actions; BLender does
not allow to have Shape Ipo Curves and Shape actions at the same
time.
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