But where does it say that it has to be done like that? There are a lot of functions that map [0, 2³² - 1] to [0, 84]⁵ or to [0, 85⁵ - 1] which they at least im

But where does it say that it has to be done like that? There are a lot of functions that map [0, 2³² - 1] to [0, 84]⁵ or to [0, 85⁵ - 1] which they at least imply by mentioning the base-85 representation. There is of course the canonical mapping, the identity function, but it never says that we are supposed to use it.