If you have a significant number of variants, then it may be desirable to impose some kind of hierarchy, e.g., cities within countries. You can use collections of variants to impose this hierarchy, just as you might for related elements within a model.
Sub-aggregation within replicated elements
For each collection of variants, the expanded model will contain a set of collections of replicated elements. There will be one collection for each element in the template, containing one replica for each variant in the original collection of variants. These sets will be laid out according to the position of the original collections relative to the original variants – try it!