1 Long: http2-prior-knowledge
5 Mutexed: http1.1 http1.0 http2
7 Help: Use HTTP 2 without HTTP/1.1 Upgrade
9 Tells curl to issue its non-TLS HTTP requests using HTTP/2 without HTTP/1.1
10 Upgrade. It requires prior knowledge that the server supports HTTP/2 straight
11 away. HTTPS requests will still do HTTP/2 the standard way with negotiated
12 protocol version in the TLS handshake.