Sites indicate which application-layer protocols they support using NPN/ALPN. If a site indicates HTTP/2, we call this announced support. more...
Some sites that announce HTTP/2 support immediately downgrade the connection to HTTP 1.1 if a client makes a request using HTTP/2. If a site responds using HTTP/2, even just to return an error page or redirect, we classify this as partial support.
If a site actually serves page content using HTTP/2, even if some embedded objects are still served over HTTP 1.1, we call this true support.