CoppeliaSim is a highly customizable simulator: almost every step of a simulation is user-defined. Additionally, the simulator itself can also be customized to a large extent. This flexibility is allowed through an integrated script interpreter. The scripting language is Lua, which is an extension programming language designed to support general procedural programming. For more information on Lua, refer to the Lua crash course section and the online documentation. By default, CoppeliaSim uses the official and original Lua, but if you wish you can tell CoppeliaSim to use another flavor of Lua by setting variable useExternalLuaLibrary in system/usrset.txt to true. In that case, all Lua calls are handled via the simLua library, which itself will link against LuaJIT (Lua Just-in-Time compiler). The simLua library project files are located here. See here for acknowledgments and credits related to Lua and LuaJIT.
CoppeliaSim extends Lua's commands and adds CoppeliaSim specific commands that can be recognized by their sim-prefixes (e.g. sim.getObjectPosition). For a list of all CoppeliaSim specific Lua-commands, refer to the regular API. New, customized Lua-commands can also be registered from a plugin. Refer to the related API-functions for more information.
Lua's functionality itself can easily be extended by making use of a Lua extension library available online.
Several types of scripts are supported in CoppeliaSim: the sandbox script, add-ons, and embedded scripts (themselves composed of a main script, child scripts and customization scripts). An embedded script is a script that is embedded in a scene (or model), i.e. a script that is part of the scene and that will be saved and loaded together with the rest of the scene (or model). On the other hand, the sandbox script and add-ons are not associated with any specific scene, model or object, and will run across all scenes in a similar way.
CoppeliaSim scripts may be published under any license.