docs/WEBSOCKET.md: explain the URL use

Fixes #9936
Closes #9941

diff --git a/docs/WEBSOCKET.md b/docs/WEBSOCKET.md
index f44f838eac1dfdb3ae9946c43503d849bb9c79a1..a52588d5482683347208a596598398d97d76761f 100644 (file)
--- a/docs/WEBSOCKET.md
+++ b/docs/WEBSOCKET.md
@@ -6,6 +6,21 @@ SPDX-License-Identifier: curl
 
 # WebSocket in curl
 
+## URL
+
+WebSocket communication with libcurl is done by setting up a transfer to a URL
+using the `ws:/` or `wss://` URL schemes. The latter one being the secure
+version done over HTTPS.
+
+When using `wss://` to do WebSocket over HTTPS, the standard TLS and HTTPS
+options will be acknowledged for the CA, verification of server certificate
+etc.
+
+WebSocket communication is done by upgrading a connection from either HTTP or
+HTTPS. When given a WebSocket URL to work with, libcurl considers it a
+transfer failure if the upgrade procedure fails. This means that a plain HTTP
+200 response code is considered an error for this work.
+
 ## API
 
 The WebSocket API is described in the individual man pages for the new API.