This etymology is missing or incomplete. Please add to it, or discuss it at the Etymology scriptorium. Particularly: “R:sw:Kraska-Szlenk:2023 claims: "the preposition ndani ‘in, within’ which historically developed from *nda ‘stomach’ combined with the locative suffix -ni." This claims appears to be from World Lexicon of Grammaticalization (2019, 2nd ed) on page 71 but I don't see a reference there”