Factorio Forums

https://lua-api.factorio.com/latest/aux ... pendencies
While the behaviour of other dependencies is somewhat clear from their name, the behavioir of recommended dependencies does not seem to be explained anywhere, and its not clear what's the difference between it and optional dependencies.
It should be added that the recommended mod will automatically be downloaded or turned on, but can be disabled.

Thinking about it more, the behaviour of other dependencies is also not very clear. Incompatible dependencies for example do not say what they do.
Also, the "(and disabled)" part of this text:

If a version is used for an optional dependency, the mod is considered incompatible (and disabled) if the dependency is present but does not fulfill the version requirement.

Makes it seem like the mod will be disabled, but if i remember right, it will make the game error instead.