Change:
an explicit interface to control prioritization, or derive the prioritization decision from the reliability level of the stream. <ins> 4.4. Flow control provides a means of managing access to the limited buffers endpoints have for incoming data.  This mechanism limits the amount of data that can be in buffers in endpoints or in transit on the network.  However, there are several ways in which limits can produce conditions that can cause a connection to either perform suboptimally or deadlock. Deadlocks in flow control are possible for any protocol that uses QUIC, though whether they become a problem depends on how implementations consume data and provide flow control credit. Understanding what causes deadlocking might help implementations avoid deadlocks. Large messages can produce deadlocking if the recipient does not process the message incrementally.  If the message is larger than flow control credit available and the recipient does not release additional flow control credit until the entire message is received and delivered, a deadlock can occur.  This is possible even where stream flow control limits are not reached because connection flow control limits can be consumed by other streams. A common flow control implementation technique is for a receiver to extend credit to the sender as a the data consumer reads data.  In this setting, a length-prefixed message format makes it easier for the data consumer to leave data unread in the receiver's buffers and thereby withhold flow control credit.  If flow control limits prevent the remainder of a message from being sent, a deadlock will result. A length prefix might also enable the detection of this sort of deadlock.  Where protocols have messages that might be processed as a single unit, reserving flow control credit for the entire message atomically ensures that this style of deadlock is less likely. A data consumer can read all data as it becomes available to cause the receiver to extend flow control credit to the sender and reduce the chances of a deadlock.  However, releasing flow control credit might mean that the data consumer might need other means for holding a peer accountable for the state it keeps for partially processed messages. Deadlocking can also occur if data on different streams is interdependent.  Suppose that data on one stream arrives before the data on a second stream on which it depends.  A deadlock can occur if the first stream is left unread, preventing the receiver from extending flow control credit for the second stream.  To reduce the likelihood of deadlock for interdependent data, the sender should ensure that dependent data is not sent until the data it depends on has been accounted for in both stream- and connection- level flow control credit. Some deadlocking scenarios might be resolved by cancelling affected streams with STOP_SENDING or RST_STREAM.  Cancelling some streams results in the connection being terminated in some protocols. </ins> 5. As QUIC is a general purpose transport protocol, there are no

Discussion:
This provides some advice about flow control and how it might produce deadlocks. This was originally quicwg/base-drafts.
lgtm modulo NAME nitsnits.