internal void Initialize(DependencyObject d, DependencyProperty dp)
        {
            Debug.Assert(_dependencyObject == null);
            Debug.Assert(_dependencyProperty == null);

            Animatable a = d as Animatable;

            if (a != null)
            {
                _dependencyObject = a.GetWeakReference();
            }
            else
            {
                //

                _dependencyObject = new WeakReference(d);
            }

            _dependencyProperty = dp;
        }