How would you know whether an ancient culture had zero? (johndcook.com)

Zero has two roles: as a positional placeholder and as a cardinal value (nothingness or net-zero). This only addresses the former.

Looks like translating a positional numbering system from ancient cultures than ruling out or not if they had the concept of zero. It may be a single use symbol, here is nothing, instead of being part of bigger amounts. Numbering systems doesn't have to be positional (nor go too far).

> If you knew somehow that some symbol corresponds to 20, then you’d know they didn’t use base 20 because base b doesn’t have a single symbol for b.

Well, this is plainly false.

What I wonder is: why has nobody noticed that code editors lack a concept of 0?

When you're writing code, you can express any concept except that of an unfilled hole. We've rearranged every part of the coding process in a twisted-up way, all for the lack of a way to express lack.

If you want to be more clear about what I mean, look to tools which can express holes like https://scratch.mit.edu and https://hazel.org. They give the feeling of letting things snap together like lego bricks. Indeed, lego bricks themselves function because of the negative space (the holes) in them!