They've been publishing a lot of the alleged source code to their CFN providers of late, so one can see how the sausage is made: https://github.com/aws-cloudformation?q=aws-cloudformation-r...

I say alleged because who knows if that's the code that's really running. And related to this current thread even if it is the code, with this being Amazon who knows if I ever found a bug and PR-ed it that it wouldn't /dev/null for 5 years before being closed by some stale-issue-bot or something