Rank:
a. CAS has rank counting from 0 because we need to know the most specific level and build up from there - see https://github.com/cellannotation/cell-annotation-schema/blob/main/docs/user_stories.md#bican use case 1. We also have non-ranked labelsets
b. ABC has Order which starts from the top down. Reasons for this: Functionality of ABC atlas (but might not be needed if order is derivable from rank, which it is); Users found counting from bottom up confusing. Order is intended for visualization.
c. Conclusion:
This can be derived from rank, so easily added to CAS->ABC converter whoever writes it.