Genres are constituted by many things besides form. But form is nonetheless an extremely important component of genre.
Form is empty, an absence.
In human beings, at least, this emptiness creates a desire to find what might fill it. One function of discourse communities is to provide, prescribe, and prefer forms. Learning conventional forms . This puts a significantly different spin on the idea of genre, locating the social practices of a discourse community more securely in the formal shape of its documents than other genre theories might wish to. In one sense, hypertexts have no formal shape.