cPlugin_NewLua: why is it Lua-exported?

[xoft]

I'm having a hard time understanding why the entire cPlugin_NewLua class is exported to Lua. Especially the callback, OnBlockDig() et al. Why would anything from Lua call these? Even worse, there doesn't seem to be a way to get the object instance on which to call the functions.

I need some serious light-shedding here.