One may want to be able to just index their data given some custom logic (such as using a set of enumerated values or a string, or really anything that isn't provided by the numeric index strategy as it is now). While there are ways currently to add this logic, the third-party code is not as straightforward as it could be. Ideally there is can just be an interface that needs to be implemented (with arbitrary provided logic) to provide InsertionIds from entries and to provide QueryRanges from a known constraint type, then queries should be able to work on that index that match the known constraint type.