short header packet needs to be the last one

draft-ietf-quic-transport.md

@@ -694,7 +694,8 @@ sequence of frames, as described in {{frames}}.
 A sender can combine multiple QUIC packets (typically a Cryptographic Handshake
 packet and a Protected packet) into one UDP datagram.  This can reduce the
 number of UDP datagrams required to be emitted when application data can be sent
-during the handshake.
+during the handshake.  A packet with a short header does not include a length,
+so it has to be the last packet included in a UDP datagram.
 
 The sender MUST NOT combine QUIC packets belonging to different QUIC
 connections into a single UDP datagram.