The idea is to represent each note in 12-TET as a number, so N ∈ (0,1,2,3,4,5,6,7,8,9,X,Y).
I used codex to build a music score rendering backend based on MuseScore with custom note heads that display the pitch class of each note.
I've found it pretty helpful for learning how to play my own instrument, so wanted to share in case anyone else was interested.