In the Prosemirror example (demo) accessed via Prosmirror's Dokuwiki plugin page I was able to create an ordered list which included a sub-ordered list which utilitzed a built-in numbering schema ... such as this:
- item 1 (accomplished via - item 1)
- item 2
a. item 2a (accomplished via [space]- item 2a)
b. item 2b
- item 3 (accomplished via - item 3)
Using my Prosemirror plugin in my Dokuwiki, no sub-ordering is achieved using the same as shown above.