Purpose of item slot right of fuel bar in of locomotive?

[Usul]

Hello!

I was manually driving a locomotive and stopped next to ore-loading inserters. I noticed that an inserter had placed some ore into the locomotive.

This raised two questions:

- What is the purpose of the item slot in the fuel tab of the locomotive UI, on the right hand side of the fuel consumption bar, which has no tooltip indicating it's use?

- Why do other types of vehicles (e.g. car, tank) do not have this item slot?

If nobody can provide plausible answers, then the existense of this item slot might be a bug.

2025-02-23_20-14-36.png (149.13 KiB) Viewed 270 times

[boskid]

copper-ore item is marked as spoil product of copper-bacteria due to gleba. If you happened to have an inserter with copper-ore in the hand, when a locomotive with burner energy source appeared under it, the burner rejected this item as a fuel but since it is a spoil product, it was inserted into output inventory so a different inserter can take it out. Otherwise the inserter could get stuck in some cases.

[Usul]

Wow, thank you for the explanation! So the "mysterious" item slot indeed has a purpose.