We want to get rid of some technical debt in Cite, caused by a consolidation of footnote numbering into ve.dm.MWDocumentReferences. The problem is that data about the InternalList and refs is being cached outside of the class, so we need to tap into update events and maintain a singleton object which can be retrieved from the document. Then, each ve.dm.MWReferenceNode is reponsible for finding its own numbering in the cached structure.
Instead, we want to push numbering responsibility down into an updateGroups event observer in InternalList, which recalculates numbers and pushes the result into the corresponding InternalItem, where it can be easily accessed by the ve.ce.MWReferenceNode. Top-level indexes will be stored as a 1-element array eg. [ 1 ] and subreference indexes will be a pair of top-level, subref indexes like [ 1, 3 ].
The ve.ce.MWReferenceNode is responsible for turning the index into a content-language (with optional group) rendered number. We still aren't supporting custom group numbering here, for the moment.