Part of the Onyx spec.
Onyx uses a non-standard layout inspired by the TPSteno Layout (found at https://github.com/StrawberryTurtle/TPSteno).
You can find the layout at https://github.com/Grahp/plover-onyx-Layout
The layout strictly requires 18 keys: 2 for each finger, 1 for each pinky.
The recommended layout uses 23 keys, with a minimal 18 key layout and steno machine-compatible layout being provided as alternatives.
(Insert charts here)