What is the purpose of Suricata rules which have sid 2200000-2299999?

Rules
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Hi, everyone.
I’m a Suricata beginner.

I would like to find security incidents by using Suricata.
I have tested Suricata which is applied ET Pro rules in pcap offline mode.
PCAP includes malware traffic and so on.
After running Suricata, I checked fast.log and found the sid of almost alerts were 2200000-2299999.
All alerts count was 1760849, and the alerts count of sid 2200000-2299999 was 1711547.

My questions are below.

  1. What is the purpose of Suricata rules which have sid 2200000-2299999?
  2. My purpose of using Suricata is for finding security incidents.
    Are these rules are helpful?
    If possible, could you tell me your usecase?