http2: more documentation for prior knowledge

(HTTP) Tells curl to issue its requests using HTTP 2. This requires that the

underlying libcurl was built to support it. (Added in 7.33.0)

.IP "--http2-prior-knowledge"

(HTTP) Tells curl to issue its requests using HTTP 2 without HTTP/1.1 Upgrade. 

This requires prior knowledge that the server supports HTTP 2.

This requires that the underlying libcurl was built to support it. 

(Added in 7.49.0)

(HTTP) Tells curl to issue its non-TLS HTTP requests using HTTP/2 without

HTTP/1.1 Upgrade. It requires prior knowledge that the server supports HTTP/2

straight away. HTTPS requests will still do HTTP/2 the standard way with

negotiated protocol version in the TLS handshake.

HTTP/2 support in general also requires that the underlying libcurl was built

to support it. (Added in 7.49.0)

.IP "--no-npn"

Disable the NPN TLS extension. NPN is enabled by default if libcurl was built

with an SSL library that supports NPN. NPN is used by a libcurl that supports

.\" *                            | (__| |_| |  _ <| |___

.\" *                             \___|\___/|_| \_\_____|

.\" *

.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.

.\" * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.

.\" *

.\" * This software is licensed as described in the file COPYING, which

.\" * you should have received as part of this distribution. The terms

Attempt HTTP 2 over TLS (HTTPS) only. libcurl will fall back to HTTP 1.1 if

HTTP 2 can't be negotiated with the HTTPS server. For clear text HTTP servers,

libcurl will use 1.1. (Added in 7.47.0)

.IP CURL_HTTP_VERSION_2_PRIOR_KNOWLEDGE

Issue non-TLS HTTP requests using HTTP/2 without HTTP/1.1 Upgrade. It requires

prior knowledge that the server supports HTTP/2 straight away. HTTPS requests

will still do HTTP/2 the standard way with negotiated protocol version in the

TLS handshake.

.SH DEFAULT

CURL_HTTP_VERSION_NONE

.SH PROTOCOLS