We've decided that the initial release of Book Referencing won't have any new VisualEditor logic to edit or render subreferences (TODO: team to confirm). However, we can't regress what VE integration Cite already has.
- Define fallback rendering for subreferences in VE. E.g., they have sequential numbering and no indentation.
- Define fallback editing behavior and edge cases for subreferences in VE.
- Browser tests to guarantee that current VE integrations still work.
- Browser tests for subref fallback behaviors in VE.