Raymond Williams believed that everything in society is worthy of study as part of culture and that there is no real difference between high culture like art and popular culture like media. Examples are provided of how high and popular culture can mix, such as an anime version of Shakespeare's Romeo and Juliet and how Salvador Dali incorporated popular graffiti into his painting of the Mona Lisa. Marcel Duchamp's "Urinal" artwork also blends popular culture, using a common urinal, with high art by placing it in a gallery. Culture is shown to have rules through various activities, though postmodernism challenges traditional rules and boundaries of culture.