Modern classical music is music written in the 20th century and beyond. Although much of it draws heavily on earlier forms, modern composers also experimented with rejection of long-held ideas; notably, Arnold Schoenberg questioned the traditional notions of harmony with his twelve-tone system[?], and John Cage questioned the very definition of music with his use of chance and found sounds.
... deemed by copyright holders to be unacceptable. See Professor Edward Felten's freedom-to-tinker Web site for information and pointers.
An early example of a DRM system ...