MARC21       008c'18-19  Form of composition
     Values: 
             an   Anthems
             bg   Bluegrass music
             bl   Blues
             bt   Ballets
             ca   Chaconnes
             cb   Chants, Other religions
             cc   Chant, Christian
             cg   Concerti grossi
             ch   Chorales
             cl   Chorale preludes
             cn   Canons and rounds
             co   Concertos
             cp   Chansons, polyphonic
             cr   Carols
             cs   Chance compositions
             ct   Cantatas
             cy   Country music
             cz   Canzonas
             df   Dance forms
             dv   Divertimentos, serenades, cassations, divertissements, notturni
             fg   Fugues
             fm   Folk music
             ft   Fantasias
             gm   Gospel music
             hy   Hymns
             jz   Jazz
             mc   Musical revues and comedies
             md   Madrigals
             mi   Minuets
             mo   Motets
             mp   Motion picture music
             mr   Marches
             ms   Masses
             mu   Multiple forms
             mz   Mazurkas
             nc   Nocturnes
             nn   Not applicable
             op   Operas
             or   Oratorios
             ov   Overtures
             pg   Program music
             pm   Passion music
             po   Polonaises
             pp   Popular music
             pr   Preludes
             ps   Passacaglias
             pt   Part-songs
             pv   Pavans
             rc   Rock music
             rd   Rondos
             rg   Ragtime music
             ri   Ricercars
             rq   Requiems
             sg   Songs
             sn   Sonatas
             sp   Symphonic poems
             st   Studies and exercises
             su   Suites
             sy   Symphonies
             tc   Toccatas
             ts   Trio-sonatas
             uu   Unknown
             vr   Variations
             wz   Waltzes
             zz   Other