Given the following MirrorMaker 2 configuration snippet, what is the effect?

Given the following MirrorMaker 2 configuration snippet, what is the effect?

{
  "clusters": {
    "A": {"bootstrap.servers": "a.kafka:9092"},
    "B": {"bootstrap.servers": "b.kafka:9092"}
  },
  "mirrors": [{"source.cluster": "A", "target.cluster": "B", "topics": ["orders"]}]
}