Because it is part of a mod that is only released to select few at the present time.
And the source code is unstable for the lua built in, that is why you dont get to see it.
Plus, building lua scripts itself doesn't require the mod. They don't need to be compiled lol.
If you really wanna see it, can talk to me in private.
Give details as to why you wish to use/see though.
I based mine off of the basic implementation of Xreal's server-side LUA code.