A lot of orchestral releases give information on the orchestra's leader/concertmaster for that recording. Similarly, orchestra sites fairly often provide information about the concertmaster position. As WP says, "The concertmaster [...] is the second-most significant person in an orchestra" - so we probably should allow to record this information. For that we should add a "concertmaster" attribute to the artist-artist "member of" relationship, to relate the people to the orchestras (since concertmasters are usually first violin or whatever, but in any case a member of the orchestra).