**KS:** See Keyslot.
+**KU:** Key update. See also TXKU, RXKU.
+
**Locally-initiated:** Refers to a QUIC stream which was initiated by the local
application rather than the remote peer.
budget should be generated. Exists in both connection-level and stream-level
instances.
+**RXKU:** RX key update. The detected condition whereby a received packet
+has a flipped Key Phase bit, meaning the peer has initiated a key update.
+Causes a solicited TXKU. See also TXKU.
+
**RXL:** RXE list. See RXE.
**RCMPPL:** The number of bytes left in a packet whose payload we are currently
**TXFC:** TX flow control. This determines how much can be transmitted to the
peer. Exists in both connection-level and stream-level instances.
+**TXKU:** TX key update. This refers to when a QTX signals a key update for the
+TX direction by flipping the Key Phase bit in an outgoing packet. A TXKU can be
+either spontaneous (locally initiated) or in solicited (in response to receiving
+an RXKU). See also RXKU.
+
**TXL:** TXE list. See TXE.
**TXP:** TX packetiser. This is responsible for generating yet-unencrypted