From the ID3v2.4 specifications:
Code:
4.2.2. Involved persons frames
TPE1
The 'Lead artist/Lead performer/Soloist/Performing group' is
used for the main artist.
TPE2
The 'Band/Orchestra/Accompaniment' frame is used for additional
information about the performers in the recording.
TPE3
The 'Conductor' frame is used for the name of the conductor.
TPE4
The 'Interpreted, remixed, or otherwise modified by' frame contains
more information about the people behind a remix and similar
interpretations of another existing piece.
TOPE
The 'Original artist/performer' frame is intended for the performer
of the original recording, if for example the music in the file
should be a cover of a previously released song.
TEXT
The 'Lyricist/Text writer' frame is intended for the writer of the
text or lyrics in the recording.
TOLY
The 'Original lyricist/text writer' frame is intended for the
text writer of the original recording, if for example the music in
the file should be a cover of a previously released song.
TCOM
The 'Composer' frame is intended for the name of the composer.
TMCL
The 'Musician credits list' is intended as a mapping between
instruments and the musician that played it. Every odd field is an
instrument and every even is an artist or a comma delimited list of
artists.
TIPL
The 'Involved people list' is very similar to the musician credits
list, but maps between functions, like producer, and names.
TENC
The 'Encoded by' frame contains the name of the person or
organisation that encoded the audio file. This field may contain a
copyright message, if the audio file also is copyrighted by the
encoder.
So that's what Martin Nilsson and Michael Mutschler (plus all the other people mentioned in
http://www.id3.org/Contributors) had in mind. Kind of an overkill when comparing this to the minimal set of recommend fields that Vorbis Comment has:
http://www.xiph.org/vorbis/doc/v-comment.html