From https://docs.google.com/spreadsheets/d/1afugW3R1FRDN-mwt5SQLY4R7aLAu3RqzjN3pR1497Ok/edit?usp=sharing I see that Picard now support the Artists field for storing multiple artists, and i think this is fairly recent that it is part of the standard build ?
I request that for ID3 it is changed from TXXX:Artists to TXXX:ARTISTS for two reasons
1.This was first added by Jaikoz/SongKong and it should always be preferred to use the existing method when one already exists as I have always strived to do.
2. Tools that convert files from one format to another deal with custom metadata quite simply. So for example if a WAV file was converted with popular dbPoweramp to Flac TXXX:Artists would become Artists, whereas in your mapping you want it to become ARTISTS (i.e UPPERCASE). Whereas if you used my solution TXXX:ARTISTS would be correctly converted to _ARTISTS _and vice versa. The sentence case used in ID3 by many MusicBrainz fields has no logical advantage and this very real disadvantage. So since artists fields has not been in PIcard for that long I ask that you rename it.