In its narratological sense, metalepsis, first identified by Genette, is a deliberate transgression between the world of the telling and the world of the told: "any intrusion by the extradiegetic narrator or narratee into the diegetic universe (or by diegetic characters into a metadiegetic universe, etc.), or the inverse […], produces an effect of strangeness that is either comical […] or fantastic" ([1972] 1980: 234-35). After reviewing a few examples, Genette observes that "[a]ll of these games, by the intensity of their effects, demonstrate the importance of the boundary they tax their ingenuity to overstep, in defiance of verisimilitude-a boundary that is precisely the narrating (or the performance) itself: a shifting but sacred frontier [or boundary] between two worlds, the world in which one tells, the world of which one tells. […] The most troubling thing about metalepsis indeed lies in this unacceptable and insistent hypothesis that the extradiegetic is perhaps always diegetic and that the narrator and his narratees-you and I-perhaps belong to some narrative" (236, original emphasis). Described as "taking hold of (telling) by changing level" (235, n. 51)
, narrative metalepsis combines the principle of narrative levels (Pier → Narrative Levels [1]) with "author's metalepsis," a narrative figure with roots in the trope of metalepsis. Narrative metalepsis constitutes a "deliberate transgression of the threshold of embedding […]: when an author (or his reader)introduces himself into the fictive action of the narrative or when a character in that fiction intrudes into the extradiegetic existence of the author or reader, such intrusions disturb, to say the least, the distinction between levels," producing an effect of "humor" or of "the fantastic" or "some mixture of the two […], unless it functions as a figure of the creative imagination" (Genette [1983] 1988: 88).These definitions, which remain foundational, providing the basis for a narrative category which, up to the early 1970s, had never been properly formulated, have been expanded, amended and refined by subsequent research, partly by Genette himself in his book Métalepses (2004), an exploration of the phenomenon not only in narrative fiction but also in theater, film, television, painting and photography.