It also usually includes Aldono al la Dua Libro (Supplement to the Second Book), which was originally published separately.

[3] After the publication of Dua Libro in early 1888, Zamenhof decided that there was no need for all the other planned volumes, and instead, in June 1888, he published just one more document to answer some questions he received and to solidify the final form of the language, titled Aldono al la Dua Libro (Supplement to the Second Book), often simply called Aldono (Supplement).

[4] Dua Libro consists of an introduction and three parts, with most versions also including the separately published Aldono at the end of the book.

The texts include collections of model sentences, a translation of "The Shadow" by Hans Christian Andersen, some popular sayings, and two poems—"Kanto de studentoj" and "El Heine'".

In Aldono, the only change Zamenhof made to the language is the spelling of the endings of the temporal correlative words (when, then, sometime, always, and never) from -ian to the current -iam.