[novatype]

> Base64 isn't numeric it's alphanumeric.

They meant that a number written in hex (base16) is still a number, even though you use some letters. Similarly, a number written in base64 is still a number.

[alkonaut]

Yes, and in that case I’d like it of Copilot erased/replaced any string over (say) 15 or 20 characters unless they are [0..9]+.

Obviously any string is a potential number in some encoding so the only encoding to exclude would be decimal.