"[The] dominant of postmodernist fiction is ontological. That is, postmodernist fiction deploys strategies which engage and foreground questions like ... "Which world is this? What is to be done in it? Which of my selves is to do it?" Other typical postmodernist questions bear either on the ontology of the literary text itself or on the ontology of the world which it projects, for instance: What is a world?; What kinds of worlds are there, how are they constituted, and how do they differ?; What happens when different kinds of worlds are placed in confrontation, or when boundaries between worlds are violated?; What is the mode of existence of a text, and what is the mode of existence of the world (or worlds) it projects?; How is a projected world structured? And so on."
-- Brian McHale, Postmodernist Fiction (info)