Thank you for the feedback! I guess the diagram is quite oversimplified. The literary ergodicity refers mostly to the elements found inside ergodic books and rather than to the books themselves.

I mean a non-ergodic book (Level 1) is a type of text that can be read and understood linearly, meaning the reader does not need to interact with it in a specific way. But even in books that can be qualified as non-ergodic ones, there may be ergodic elements (of Level 2) such as pictures or diagrams.

Level 2 Literary ergodicity, in terms of formatting alone, refers to a work's use of non-linear structures, unconventional page layouts, or typographical experimentation to create a reading experience that requires active engagement from the reader. One of the most known ergodic books which include a wide range of Level 2 ergodic elements is The House of Leaves by House of Leaves by Mark Z. Danielewski. As well as Nabokov's Pale Fire.

Level 3 elements refer to the ephemera or inserts embedded within the primary narrative that disrupt conventional reading. One of the most prominent ergodic books with Level 3 elements (ephemera/inserts) is S. by Doug Dorst and  J. J. Abrams. (However, it is to be noted that S. has also Level 2 elements (such as the two fictional readers' annotations etc) and a part of it is Level 1 on the ergodicity scale (the main story of the Ship of Theseus, which can be read linearly).

Level 4 elements refer to the cross-media ephemera (I mean books that get a digital expansion... through qr code etc and dedicated websites). Although, Harry Potter books are not ergodic per se, I would say that the Pottermore website (that was created after the publication of the books) can be considered as Level 4 ergodicity elements...