What is the difference between peer and force_peer

Elastic Stack Logstash
1

logstash input settings, the document is described:

ssl_verify_mode

peer will make the server ask the client to provide a certificate, if the client provides a certificate it will be validated.

force_peer will make the server ask the client to provide a certificate. If the client doesn’t provide a certificate, the connection will be closed.

What is the difference between peer and force_peer

2

force_peer requires the client to provide a certificate while that's optional in the peer case. Provided certificates will be validated in both cases.