Returns the object which is driving the action or shape
animation. This could be any object derived from SIObject which is driving the action or shape
animation. This property is not available for compound clips. You
can test to see whether the clip is a compound clip by calling the
base method SIObject.IsClassOf(siClipContainerID)
on the Clip object.
Warning: In the case of Expressions or Constraints, this property
will fail, reporting that it is not implemented (returns E_NOTIMPL)
because the MappedItem object does not contain the full Expression or Constraint objects.