How does "connection rate bursts" for MSK work?

See https://docs.aws.amazon.com/msk/latest/developerguide/limits.html. Could you please explain what "connection rate bursts" is? If I google for it, I get just this page and the link mentioned here. The questions I have:

1. Is the limit per broker or per cluster?
2. How long can kafka.t3.small sustain 4 new TCP connections per second?
3. What happens if I have reconnect.backoff.ms too low on a client? Will attempts that are rejected negatively affect the number of successful connections?
4. What is the base rate once the burst budget (if it works like that) is depleted?
5. How fast will credits be added to the burst budget (if it works like that)?