cmavo which are officially unassigned, excluding experimental cmavo.
bo'X is the only series of a-e-i-o-u left, and zi'X is the only series of i-a-u left, so they shouldn't be touched without very good reason.
- po'a is included in the 1994 version of cmavo list, but not in the 1998 one. Is it assigned or not? --kir