Code change:
Priority handling of retransmissions can be implemented by the sender in the transport layer.  QUIC recommends retransmitting lost data before new data, unless indicated differently by the application. <del> Currently, QUIC only provides fully reliable stream transmission, which means that prioritization of retransmissions will be beneficial in most cases, by filling in gaps and freeing up the flow control window.  For partially reliable or unreliable streams, priority scheduling of retransmissions over data of higher-priority streams might not be desirable.  For such streams, QUIC could either provide an explicit interface to control prioritization, or derive the prioritization decision from the reliability level of the stream. </del> <ins> When a QUIC endpoint uses fully reliable streams for transmission, prioritization of retransmissions will be beneficial in most cases, filling in gaps and freeing up the flow control window.  For partially reliable or unreliable streams, priority scheduling of retransmissions over data of higher-priority streams might not be desirable.  For such streams, QUIC could either provide an explicit interface to control prioritization, or derive the prioritization decision from the reliability level of the stream. </ins> 4.3.

Related discussion:
text: From PR : I'd also like to see something like : /In this section, we discuss those aspects of the QUIC transport protocol that/This section discusses those aspects of the QUIC transport protocol that/ /Here, we are concerned primarily with the unencrypted part of QUIC's wire image {{WIRE-IMAGE}}, which we define as the information available in the packet/This section is concerned primarily with the unencrypted part of QUIC's wire image {{WIRE-IMAGE}}, defined as the information available in the packet/ and /least four datagrams we'll call "Client Initial",/least four datagrams, labelled "Client Initial",/ and / 0-RTT data may also be seen in the Client Initial datagram, as shown in /When the client uses 0-RTT connection resumption, the Client Initial datagram can also carry 0-RTT data, as shown in/ and /typically around 10 packets/typically to around 10 packets/ and /of a connection after one of one endpoint/of a connection after an endpoint/ I'd prefer more like: /Though the guidance there holds, a particularly unwise behavior admits a handful of UDP packets and then makes a decision as to whether or not to filter later packets in the same connection. QUIC applications are encouraged to fail over to TCP if early packets do/ ... and I'll close PR .
“QUIC exposes some information to the network in the unencrypted part of the header, either before the encryption context is established or because the information is intended to be used by the network.” Could this benefit form a cross-reference to manageability, where this topic is also discussed from a network perspective?
Three places where the text might avoid confusion when read in future years: 1) “Further downgrades to older TLS versions than used in QUIC, which is 1.3, “ … will it always be 1.3, or should this be “in QUIC [REF] is TLS 1.3” 2) “Currently, QUIC only provides fully reliable stream transmission, which means that prioritization of retransmissions will be beneficial in most cases, by filling in gaps and freeing up the flow control window.