Change:
QUIC's loss detection algorithm determines that the quoted packet has actually been lost. <del> 14.3. </del> <ins> 14.2. Datagram Packetization Layer PMTU Discovery (DPLPMTUD; DPLPMTUD) relies on tracking loss or acknowledgment of QUIC packets that are carried in PMTU probes.  PMTU probes for DPLPMTUD that use the PADDING frame implement "Probing using padding data", as defined in Section 4.1 of DPLPMTUD. Endpoints SHOULD set the initial value of BASE_PMTU (see Section 5.1 of DPLPMTUD) to be consistent with the minimum QUIC packet size.  The MIN_PLPMTU is the same as the BASE_PMTU. QUIC endpoints implementing DPLPMTUD maintain a maximum packet size (DPLPMTUD MPS) for each combination of local and remote IP addresses. 14.2.1. </ins> <del> Section 6.3 of DPLPMTUD provides considerations for implementing Datagram Packetization Layer PMTUD (DPLPMTUD) with QUIC. </del> <ins> From the perspective of DPLPMTUD, QUIC transport is an acknowledged packetization layer (PL).  A sender can therefore enter the DPLPMTUD BASE state when the QUIC connection handshake has been completed. </ins> <del> When implementing the algorithm in Section 5 of DPLPMTUD, the initial value of BASE_PMTU SHOULD be consistent with the minimum QUIC packet size (1232 bytes for IPv6 and 1252 bytes for IPv4). </del> <ins> 14.2.2. </ins> <del> PING and PADDING frames can be used to generate PMTU probe packets. These frames might not be retransmitted if a probe packet containing them is lost.  However, these frames do consume congestion window, which could delay the transmission of subsequent application data. </del> <ins> QUIC provides an acknowledged PL, therefore a sender does not implement the DPLPMTUD CONFIRMATION_TIMER while in the SEARCH_COMPLETE state; see Section 5.2 of DPLPMTUD. 14.2.3. An endpoint using DPLPMTUD requires the validation of any received ICMP Packet Too Big (PTB) message before using the PTB information, as defined in Section 4.6 of DPLPMTUD.  In addition to UDP port validation, QUIC validates an ICMP message by using other PL information (e.g., validation of connection IDs in the quoted packet of any received ICMP message). The considerations for processing ICMP messages described in pmtud also apply if these messages are used by DPLPMTUD. 14.3. </ins> <del> A PING frame can be included in a PMTU probe to ensure that a valid probe is acknowledged. </del> <ins> PMTU probes are ack-eliciting packets. </ins> <del> The considerations for processing ICMP messages in the previous section also apply if these messages are used by DPLPMTUD. </del> <ins> Endpoints could limit the content of PMTU probes to PING and PADDING frames as packets that are larger than the current maximum packet size are more likely to be dropped by the network.  Loss of a QUIC packet that is carried in a PMTU probe is therefore not a reliable indication of congestion and SHOULD NOT trigger a congestion control reaction; see Section 3, Bullet 7 of DPLPMTUD.  However, PMTU probes consume congestion window, which could delay subsequent transmission by an application. </ins> 14.3.1. Endpoints that rely on the destination connection ID for routing incoming QUIC packets are likely to require that the connection ID be <del> included in PMTU probe packets to route any resulting ICMP messages (icmp-pmtud) back to the correct endpoint.  However, only long header packets (long-header) contain source connection IDs, and long header </del> <ins> included in PMTU probes to route any resulting ICMP messages (pmtud) back to the correct endpoint.  However, only long header packets (long-header) contain the Source Connection ID field, and long header </ins> packets are not decrypted or acknowledged by the peer once the handshake is complete. <del> One way to construct a probe for the path MTU is to coalesce (see packet-coalesce) a Handshake packet (packet-handshake) with a short header packet in a single UDP datagram.  If the UDP datagram reaches the endpoint, the Handshake packet will be ignored, but the short header packet will be acknowledged.  If the UDP datagram causes an ICMP message to be sent, the first part of the datagram will be quoted in that message.  If the source connection ID is within the quoted portion of the UDP datagram, that could be used for routing. </del> <ins> One way to construct a PMTU probe is to coalesce (see packet- coalesce) a packet with a long header, such as a Handshake or 0-RTT packet (long-header), with a short header packet in a single UDP datagram.  If the resulting PMTU probe reaches the endpoint, the packet with the long header will be ignored, but the short header packet will be acknowledged.  If the PMTU probe causes an ICMP message to be sent, the first part of the probe will be quoted in that message.  If the Source Connection ID field is within the quoted portion of the probe, that could be used for routing or validation of the ICMP message. The purpose of using a packet with a long header is only to ensure that the quoted packet contained in the ICMP message contains a Source Connection ID field.  This packet does not need to be a valid packet and it can be sent even if there is no current use for packets of that type. </ins> 15.

Discussion:
This is with some minor additional changes: Reflow. Move the odd text about using Handshake back where it belongs. Make the language about how to construct a probe less prescriptive. Mention 1200 when referring to the "smallest allowed maximum packet size" so it is clear what that means.
NAME I went with "PMTU probe packet", which is an IP packet. Let me know if that makes sense.
OK - There are already "IP packets" and "QUIC packets" - so some other term works fro me.
A top-level comment on the term "probing": In Section: Probing a New Path: A packet containing only probing frames is a "probing packet", and a packet containing any other frame is a "non-probing packet". Please be sure that "probe" can not be confused with "probing" in PLPMTUD.
In the subsection on “Packet Size {#packet-size}”, I think the blocks of text describe two things. There is some general guidance on size, and there are specific instructions for the size of the initial packet. I’d suggest we do try to separate these two, it would make it much easier for someone to understand the size constraints for forming the initial packet.
Regarding the sizing of Initial packets, see . I checked the text for probing and we have "PMTUD probe" in one case and "probing packet" elsewhere. It's not ideal, but I didn't see any cases that were clearly busted. I don't have a good idea for alternative labels, but would welcome suggestions.
It turns out that coordinating the publication of all the documents is a real challenge. Right now, DPLPMTUD depends on QUIC, which is fine, but it turns out that this is a problem for other things that depend on DPLPMTUD who now transitively depend on QUIC. QUIC could adopt the DPLPMTUD text that is specific to QUIC and loosen this dependency chain. The text changes are relatively modest, see . While this could be editorial, I think that this will require a consensus call. The nature of the changes is such that it should be treated as design. Also, I think that there are substantive changes required.

So from an AD perspective, draft-ietf-tsvwg-datagram-plpmtud is currently blocking another document (URL) from being published that has a missref on it. Except for this question of QUIC I am ready to approve draft-ietf-tsvwg-datagram-plpmtud. To me it is also clear that integration of DPLPMTUD done in the QUIC WG will result in less editorial clarity issues that potentially could make an future implementer uncertain. As can already been seen in the PR there a few question that potentially can improve the operation and not unnecessary restrict the operation of DPLPMTUD. From my perspective it looks like the core is a set of minor editorial issues to resolve that will make the DPLPMTUD be clearer and resolve the missref issue and function as well as keeping it in the TSVWG document would. If a little bit more effort is invested after the first step then there is potential for additional improvements.