Square brackets are the default way to access table elements by key. The dot syntax only works if the key is string consisting only of alphanumeric characters and underscores. The first character has to be a letter or underscore, not a number. The same is true for variable names.

local t = {}
t ...

Hello, I'm trying to create a mod that has a higher maximum length for new underground belts. However, I'm encountering an issue with the internal and prototype name of "underground-belt" which is not recognized properly due to having the hyphen.

A makeshift solution was:
data.raw["underground ...