I'm trying to do https://mods.factorio.com/mods/galibert ... dPlacement. Square selection wouldn't work, I'll see what autofill does. Thanks for the hints.

Hi, I'm trying to build a QoL mod, which I'd like in some aspects to behave like the standard build key. Specifically, I'd like to press my binding (control-mouse-1) and make it possible to drag the mouse over a series of entities and act on them. That's similar to what build-click or fill-click do....