Jakob Voß questioned in Twitter (https://twitter.com/nichtich/status/956810925276913664)

"is there a machine-readable list of defined MARC fields and allowed subfields and if so in which form? We're just creating such list for PICA format and I'd like to compare before defining my own little schema language."

Jonathan Rols added (https://twitter.com/johrols/status/956814998671642624):

"Ok, thanks. I would be interested in a JSON export of the schema..."