Lua is a lightweight, high-level, multi-paradigm programming language designed primarily for embedding into other applications, making it ideal for scripting and rapid prototyping.
References for Lua 5.1 for Fantasy Grounds
Fantasy Grounds Scripting
https://www.fantasygrounds.com/modguide/scripting.xcp
The Lua Programming Language
Lua 5.1 Reference Manual
https://www.lua.org/manual/5.1
Lua Tutorials
http://lua-users.org/wiki/LuaTutorial