In cinema, the avant-garde refers to the films experimenting with non-traditional form and content, often completely discarding standard narrative structure to explore the possibilities of the medium as an art form. Surrealism, abstract studies of light and form, Dadaism, and impressionistic studies of people and things figure heavily in early works of the genre. More recently, the avant-garde has expanded to include underground film, so-called "trash" cinema, and even some non-traditional documentaries. Andy Warhol spanned the early days of avant-garde as well as the more recent types by moving from such films as Empire (an eight-hour portrait of the Empire State Building) to Trash, a mostly improvised swim in the cinematic gutter with New York transvestites, prostitutes, and heroin addicts.