103 Early Hints
103 Early Hints information response may be sent by a server while it is still preparing a response, with hints about the resources that the server is expecting the final response will link.
This allows a browser to start preloading resources even before the server has prepared and sent that final response.
The early hint response is primarily intended for use with the Link header, which indicates the resources to be loaded.
It may also contain a Content-Security-Policy header that is enforced while processing the early hint.
A server might send multiple
103 responses, for example, following a redirect.
Browsers only process the first early hint response, and this response must be discarded if the request results in a cross-origin redirect.
Preloaded resources from the early hint are effectively pre-pended to the
Document's head element, and then followed by the resources loaded in the final response.