Yes, by "reference counting" is really whatever I've in mind.
And if it's OK for others, I'm quite happy to make contributions to Lua 5.4 directly.
Since GC is already widely used and accepted, I just don't think I have the right to force others to get rid of the way of thinking in GC.
So whatever I do now is: provide a switch for users to use GC or disable it (then use reference counting, and default is GC enabled).
I need help to get a better understanding on where to apply reference counting (where to increase reference count and where to decrease reference count).