Is this saying that let’s say I have an iron outpost and a copper outpost and two trains set to any item. Let’s say the copper outpost has a higher priority.

If one train is unloading iron and the copper train has left the copper outpost, the iron train would decide to go to the copper outpost? And if copper fully unloaded by then, it would go to the iron outpost?

Basically, the ability to have generic trains that just move stuff without a dedicated line?