Filk is a living folk cultural category with its roots in science fiction fandom, poetry, storytelling, and especially music. Like science fiction, it is an odd superset of all other cultural categories, existing on the fringes of many. Strong themes include parody (some would say homage), lyrics only, of the sort you'd find in Mad magazine, and science fiction, fantasy, and the kind of stuff you'd find littering the lives of fans, such as computers, the space program, cats, the Society for Creative Anachronism, and stuff that is stranger than you CAN imagine. The predominant musical format is folk, but there are well-executed instances of practically anything else. As in any living folk culture, all the members can participate, though not all do, and their skill and involvement levels vary widely. Set in the modern multi-cultural matrix, it eclectically adopts elements (e.g., songs) from the surrounding culture that seem to filkers to resonate properly within their communities, which show considerable regional variation and even controversy over what their boundaries should be.