[lifthrasiir]

Functions are apparently serialized as a bytecode dump contained in a self-extracting expression. So everything can indeed be serialized as a Lua expression. Seems that the author also tried to preserve as many upvalues as possible, though I feel that is way more dangerous than I would like.

[girvel]

Yep, that is correct. I think ldump is able to preserve all upvalues, even on edge cases such as "_ENV" and joined upvalues (multiple functions referencing one upvalue). A closure is basically an object with a single method and upvalues as fields -- serialization is straightforward. I think I got it covered, but I would be glad to hear ideas about where the serialization can be unstable.