Introduction to Codebase
Prepare for the worst. You'll be either right, or pleasantly surprised.
Codebase. What a nice word for a folder filled with Poorly-But-Sometimes-Good written code. Say hello to our little friend /gamedata/scripts - here you will find every script in the game, and you will even be able to read some of them. Here are the important ones:
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_g.script- your global namespace. Everything defined here can be accessed in any script. If you don't understand where a function comes from, it's probably here. For example, here liesCreateTimeEvent. - 
lua_help.script- engine imports. It's not really a lua file, but it's important nevertheless. Every namespace defined here is globally accessible, and you better avoid name collisions with it - otherwise death is imminent. Documentation is... Not there, but some names are understandable, so you might be able to use it anyway. - 
axr_main.script- a table with all callbacks is defined there. Don't register your callbacks there, useRegisterScriptCallbackfrom_ginstead. 
These are the ones you need to know about. Every other functionality is found through global search. Ctrl-Shift-F in your favorite editor. You're welcome.