Oh I see. Well, then it’s not really bottom-up. Instead, if I understand correctly, it’s that you can move your cells in the order you want, while the order in which cells are run is determined under the hood.
You can add cells below or above, as you wish:
and you can rearrange by dragging cells around, too:
[EDIT] Note you can check the order in which cells are executed in the .jl file, which is a standard Julia script, although it has extra metadata for Pluto (including the order in which the cells appear in the Pluto interface).