It appears (from data.raw["noise-function"].expression_in_range_base) that expression_in_range is a built-in function, but it isn't documented on https://lua-api.factorio.com/latest/aux ... sions.html
Will you add documentation for this function, please?
Documentation for expression_in_range function
Re: Documentation for expression_in_range function
Done for the next version.
I'm an admin over at https://wiki.factorio.com. Feel free to contact me if there's anything wrong (or right) with it.

