Advice on making a level editor

[s-ol]

EDIT: Looked again at your example code and realized "img" is both userdata and a table key. Can you actually use that as a field?

If I understand your question correctly, yes, you can use userdata as table keys.

I had no idea. That's really interesting.

You can use functions aswell. All Lua types are created equal

[Lugen]

You can use functions aswell. All Lua types are created equal

And it works! Now I can fetch the necessary userdata for my entities when loading the level again, and when saving I only need to determine by the type of the userdata which table to look at for the metadata. I can assign the userdata to my components directly as usual.
So now it seems I can move forward.