Please answer a question about the following article about Classical music:

Classical music has often incorporated elements or material from popular music of the composer's time. Examples include occasional music such as Brahms' use of student drinking songs in his Academic Festival Overture, genres exemplified by Kurt Weill's The Threepenny Opera, and the influence of jazz on early- and mid-20th-century composers including Maurice Ravel, exemplified by the movement entitled "Blues" in his sonata for violin and piano. Certain postmodern, minimalist and postminimalist classical composers acknowledge a debt to popular music.

Popular music from the composer's time was incorporation into what?
Classical music