A New Word - Diegesis

I came across this word when reading up on Julien Donkey-Boy, a film which adheres to the Danish Dogme 95 rules for film-making. The second of the Dogme 95 rules, according to Wikipedia, states,

The sound must never be produced apart from the images or vice versa. Music must not be used unless it occurs within the scene being filmed, i.e., diegetic.

And here's how Wikipedia explains diegesis:

Diegesis (Greek `to narrate') and mimesis (Greek `imitation' or `to copy') have been contrasted since Plato's and Aristotle's times. Mimesis shows rather than tells, by means of action that is enacted. Diegesis, however, is the telling of the story by a narrator. The narrator may speak as a particular character or may be the invisible narrator or even the all-knowing narrator who speaks from above in the form of commenting on the action or the characters.

Diegesis can also refer to the fictional world of the story, the "space" which characters inhabit both within and outside of the action of the story. This makes me wonder, is there any world, in fiction, that is not diegetic?

The word's opposite, mimesis, seems more familiar. Mimes, after all "act out" their stories.

Say it like this: die-uh-djee-siss