"Genres - such as the joke, the novel, the document, and the sitcom - get picked out contrastively amid a jumble of discourse and often across multiple media because of the way they've been internalized by constituents of a shared culture. Individual genres aren't artifacts, then; they are ongoing and changeable practices of expression and reception that are recognizable in myriad and variable constituent instances at once and also across time. They are specific and dynamic, socially realized sites and segments of coherence within the discursive field."