http3.md: mention how the fallback can be h1 or h2

Closes #14736

diff --git a/docs/cmdline-opts/http3.md b/docs/cmdline-opts/http3.md
index a1900655a0ba80f9c6a3bfd38826c54b976b0694..fa3d7c38010364a6194b98c63d20b1e2d71d27ed 100644 (file)
--- a/docs/cmdline-opts/http3.md
+++ b/docs/cmdline-opts/http3.md
@@ -20,14 +20,16 @@ Example:
 # `--http3`
 
 Attempt HTTP/3 to the host in the URL, but fallback to earlier HTTP versions
-if the HTTP/3 connection establishment fails. HTTP/3 is only available for
-HTTPS and not for HTTP URLs.
+if the HTTP/3 connection establishment fails or is slow. HTTP/3 is only
+available for HTTPS and not for HTTP URLs.
 
 This option allows a user to avoid using the Alt-Svc method of upgrading to
-HTTP/3 when you know that the target speaks HTTP/3 on the given host and port.
+HTTP/3 when you know or suspect that the target speaks HTTP/3 on the given
+host and port.
 
 When asked to use HTTP/3, curl issues a separate attempt to use older HTTP
 versions with a slight delay, so if the HTTP/3 transfer fails or is slow, curl
-still tries to proceed with an older HTTP version.
+still tries to proceed with an older HTTP version. The fallback performs the
+regular negoatiaion between HTTP/1 and HTTP/2.
 
 Use --http3-only for similar functionality *without* a fallback.