The prototype docs have moved to a new website with an improved format. This documentation page can now be found here: https://lua-api.factorio.com/latest/types/FileName.html
This wiki page is no longer updated and will be removed at some point in the future, so please update your browser bookmarks or other links that sent you here. If you'd like to contribute to the new docs, you can leave your feedback on the forums.
Specified by Types/string
Slash (/) is always used as directory delimiter.
The path should always begin by the specification of the root.
Path starting with __core__ will access the resources in the data/core directory, these resources are always accessible regardless of mod specifications.
filename = "__core__/graphics/arrows/underground-lines.png"
Path starting with __base__ will access the resources in the base mod in data/base directory. These resources are usually available, as long as the base mod isn't removed/deactivated.
filename = "__base__/graphics/entity/basic-transport-belt/basic-transport-belt.png"
The format __<mod-name>__ is placeholder for root of any other mod (mods/<mod-name>), and is accessible as long as the mod is active.