ItemStack

One property-distinct stack of items. Returned by: stacks() on InputSlot, VehicleInputSlot, OutputSlot, PickupOutputSlot, Cargo, Bin, Storage Bin, and Warehouse.

Member	Returns	Meaning
.id	string	Stable item id shared by every unit in this stack
.count	number	Whole-number units with this exact property identity
.properties	dict or None	Exact property dict, or None for an ordinary commodity

Items with different properties form separate stacks and never merge. Property-aware transfers select stacks with the properties + property_match ("any" / "subset" / "exact") arguments; see Input & Output.