The Track Composer Field is not limited to classic composers. It is available for all lyrics/music composers as well.

Examples:

John Lennon/Paul McCartney
John Lennon/Yoko Ono
Gerry Goffin/Carole King
Mick Jagger/Keith Richards
Jerry Garcia/Robert Hunter
Jerry Leiber/Mike Stoller
Elton John/Bernie Taupin

and thousands of others.

The collaboration feature will for example list all songs written by John Lennon with Paul McCartney, Yoko Ono and other collaborators.