11-应用层扩展(Application-Layer-Extensions) HTTP 缓存语义、HTTP/2/3 等增量。 索引 01-HTTP缓存控制(HTTP-Cache-Control) 02-实体标签(Entity-Tag) 03-HTTP2(HTTP-2) 04-HTTP3(HTTP-3) 05-QUIC(QUIC) 06-投递语义(Delivery-Semantics) 07-死信队列(Dead-Letter-Queue) 08-背压(Backpressure)