Use this method when you want a spot on this object to be near, but not exactly at, a spot on another object, by moving this object. This is just like SetSpotLocation(Int32,GoObject,Int32), except that it first adds the dx and dy offsets to the point of the obj's otherSpot.
Remember that this method just moves this object once. When other objects in a group resize or move, this object will not automatically follow. You will need to override LayoutChildren to maintain whatever layout you want.