internal ObjectsClickedMessage(List<SceneObject> clickedObjects)
        {
            clickedObjects.EnsureNotNull("clickedObjects");
            clickedObjects.EnsureMoreThanZeroElements("clickedObjects");

            this.ClickedObjects = clickedObjects;
        }
        internal HoveredObjectsChangedMessage(
            List<SceneObject> removedObjects,
            List<SceneObject> addedObjects)
        {
            removedObjects.EnsureNotNull("removedObjects");
            addedObjects.EnsureNotNull("addedObjects");

            this.RemovedObjects = removedObjects;
            this.AddedObjects = addedObjects;
        }