Right now, foobar writes the COMPOSER field to a private data field in MP4/M4A files. Given the <WRITER> (atom "@wrt") exists, and is used by iTunes and mp3tag, among others, may I suggest that foobar should switch to the standard field instead of a using private meta data?

Also, less critically, perhaps ALBUM ARTIST should be mapped to the atom "aART" which is used by, among others, AtomicParsley.