DataGroup/Group split work. DataGroup is for holding data items that may require item rendering. Group only holds visual items now. The Group APIs stay the same (numItems, addItem, etc...). DataGroup uses the IList APIs through its dataProvider. So the equivalent methods are now dataProvider.length, dataProvider, addItem, etc... This is just the initial split work as there's more to come to get the files up to spec. We will also have to visit how we deal with graphic elements in DataGroup vs. Group. For now the implementations are roughly the same.