Free Dimension: A DimensionCluster instance, or a LocaleType instance. QUESTION: Is Free Dimension the best name? It seems so, because it is a direct correspondence with the Free/Fixed Dimension terminology that we are using in our data viz. But if we don't want to couple our UI terms with our Data Viz terms, perhaps we can call it Filter Group
Filter: A collection of Locales, or a collection of DimensionInstances, like so: <Locale>[], <DimensionInstance>[]