from http://bugs.musicbrainz.org/ticket/4122

Recently came across the iTunes Metadata Format Specification document by Apple which is freely available (but not distributable) to anyone in the adc (apple developer connection - free registration).It documents all the atoms they use in the metadata and includes a number that don't seem visible in iTunes but perhaps they are going to be added. Some of these conflict with some of the reverse dns atoms that were added in #3379 , maybe some should be same changed.

i.e
Lyricist @aut
Conductor @con
Label @mak
Producer @prd
Engineer @sne