Lua Programming/How to Lua/userdata
The userdata datatype can be used to store raw memory data in variables.
Userdata values can only be created or modified via the application interface
In lua, it is not possible to create or modify userdata except via the C application interface.
The only predefined operations that can be performed against userdata is assignment and identity testing. It is possible to define operations for userdata by using metatables
There are two forms of userdata
The datatype userdata takes two forms: Light Userdata and Heavy Userdata.