I just learned that the id3 spec does support multiple values in some (all?) fields. I found some old posts here indicating that \ is the correct separator to use in mp3tag, and it will be mapped to the correct NULL when saving.
Is this still best practice? Are there any problems standardizing on this approach? I can't find any recent discussion on the topic.
One problem that I foresee is with my file naming convention. I make %artist% part of the file name and "\" will probably get substituted with a space... to keep file names human-readable it would be great if the null could be replaced with something else like "&" when writing filenames. Is there a way to do this in mp3tag?
If anyone knows a player that understands multiple values in key fields like artist, that would be cool. It sounds like it might be part of the spec that no one supports, though.