Better way to share custom field mappings

I've never used custom tag field mappings much, but for 3GPP MP4 boxes and QT MOV atoms I wanted to try it.

I then realized that they are exported as part of the binary mp3tag.cfg. I'd like to suggest to export (and import) them as a plain-text .ini file in the /data folder.

This way, one could also, for instance, share settings for MediaMonkey users to support its custom tag fields:

Tag Type Target Source
MP4 rate POPULARIMETER
MP4 mood MOOD
MP4 isrc ISRC
MP4 lyrc LYRICIST
MP4 peop INVOLVEDPEOPLE
MP4 otit ORIGTITLE
MP4 oart ORIGARTIST
MP4 olyr ORIGLYRICIST
MP4 oday ORIGYEAR
MP4 empo BPM
MP4 publ PUBLISHER

I would also like some explicit documentation on how Mp3tag stores custom MP4 fields (TXXX;FOO in ID3v2)): as udta.----:FOO or udta.----:com.apple.iTunes:FOO? (Also see this thread for the Mac version.)

Also related: User-defined Field Mappings