/// <summary>
        /// Helper used by the four Freezable clone methods to copy the resolved key times and
        /// key frames. The Get*AsFrozenCore methods are implemented the same as the Clone*Core
        /// methods; Get*AsFrozen at the top level will recursively Freeze so it's not done here.
        /// </summary>
        /// <param name="sourceAnimation"></param>
        /// <param name="isCurrentValueClone"></param>
        private void CopyCommon(Rotation3DAnimationUsingKeyFrames sourceAnimation, bool isCurrentValueClone)
        {
            _areKeyTimesValid = sourceAnimation._areKeyTimesValid;

            if (_areKeyTimesValid &&
                sourceAnimation._sortedResolvedKeyFrames != null)
            {
                // _sortedResolvedKeyFrames is an array of ResolvedKeyFrameEntry so the notion of CurrentValueClone doesn't apply
                _sortedResolvedKeyFrames = (ResolvedKeyFrameEntry[])sourceAnimation._sortedResolvedKeyFrames.Clone();
            }

            if (sourceAnimation._keyFrames != null)
            {
                if (isCurrentValueClone)
                {
                    _keyFrames = (Rotation3DKeyFrameCollection)sourceAnimation._keyFrames.CloneCurrentValue();
                }
                else
                {
                    _keyFrames = (Rotation3DKeyFrameCollection)sourceAnimation._keyFrames.Clone();
                }

                OnFreezablePropertyChanged(null, _keyFrames);
            }
        }
        /// <summary>
        /// Implementation of <see cref="System.Windows.Freezable.CloneCore(System.Windows.Freezable)">Freezable.CloneCore</see>.
        /// </summary>
        protected override void CloneCore(Freezable sourceFreezable)
        {
            Rotation3DAnimationUsingKeyFrames sourceAnimation = (Rotation3DAnimationUsingKeyFrames)sourceFreezable;

            base.CloneCore(sourceFreezable);

            CopyCommon(sourceAnimation, /* isCurrentValueClone = */ false);
        }
        /// <summary>
        /// Implementation of <see cref="System.Windows.Freezable.GetCurrentValueAsFrozenCore(Freezable)">Freezable.GetCurrentValueAsFrozenCore</see>.
        /// </summary>
        protected override void GetCurrentValueAsFrozenCore(Freezable source)
        {
            Rotation3DAnimationUsingKeyFrames sourceAnimation = (Rotation3DAnimationUsingKeyFrames)source;

            base.GetCurrentValueAsFrozenCore(source);

            CopyCommon(sourceAnimation, /* isCurrentValueClone = */ true);
        }
        /// <summary>
        /// Helper used by the four Freezable clone methods to copy the resolved key times and 
        /// key frames. The Get*AsFrozenCore methods are implemented the same as the Clone*Core
        /// methods; Get*AsFrozen at the top level will recursively Freeze so it's not done here.
        /// </summary>
        /// <param name="sourceAnimation"></param>
        /// <param name="isCurrentValueClone"></param>
        private void CopyCommon(Rotation3DAnimationUsingKeyFrames sourceAnimation, bool isCurrentValueClone)
        {    
            _areKeyTimesValid = sourceAnimation._areKeyTimesValid;

            if (   _areKeyTimesValid 
                && sourceAnimation._sortedResolvedKeyFrames != null)
            {
                // _sortedResolvedKeyFrames is an array of ResolvedKeyFrameEntry so the notion of CurrentValueClone doesn't apply
                _sortedResolvedKeyFrames = (ResolvedKeyFrameEntry[])sourceAnimation._sortedResolvedKeyFrames.Clone(); 
            }

            if (sourceAnimation._keyFrames != null)
            {
                if (isCurrentValueClone)
                {
                    _keyFrames = (Rotation3DKeyFrameCollection)sourceAnimation._keyFrames.CloneCurrentValue();
                }
                else
                {
                    _keyFrames = (Rotation3DKeyFrameCollection)sourceAnimation._keyFrames.Clone();
                }

                OnFreezablePropertyChanged(null, _keyFrames);
            }
        }