Code change:
(well, the priority framework is still confusing, this PR makes it clear that that is intentional, and why)
Martin (I think) said that he'd check this offline after the Sep 11 interim.
At 8.1.2 you say lower values have higher priorities for connPrio. But later, at msgPrio, higher values have higher priority, and in the examples where you speak of the interaction of connPrio and msgPrio, you imply that higher means higher for both properties. Please check for consistency and clarify.
Lower values having higher priorities for connPrio is a remnant that we must have missed when we flipped this, e.g. PR which I don't know... too many iterations have mangled the text.
Aha, now I see what happened: following some more PRs, also , in PR , NAME re-introduced some text saying that sends on Connections with lower-priority values will be prioritized over sends on Connections with a higher-priority value. This reverses the logic for some part of the text - I suspect that NAME (very understandably!) forgot what happened and this created this mix. We have been editing these documents for way too long!
I'm not sure the priority framework really fits together. Sec 6.4 says we 'should' do something that sounds like WFQ, but 7.1.5 allows the application to decide what happens. Meanwhile message priority suggests a strict priority-based scheduler. Meanwhile, in sec 8.1.3.2 "Note that this property is not a per-message override of the connection Priority - see Section 7.1.3. Both Priority properties may interact, but can be used independently and be realized by different mechanisms." At the risk of overindexing on a partly-baked draft in httpbis, how would I implement strict priority of HTTP/3 streams over a taps API that implements QUIC? Would I need to request strict priority in both connection priority and message priority? Or I guess connection priority would be sufficient?
We seem comfortable with the mechanisms in the API, but we should have more text connecting the various sections explaining priority.
My comment concerned "7.1.3. Priority (Connection)", my thought was this just influences the sender-side to control queuing within a connection group. If so, if it worth calling this property "Group Priority" and explain this is sender-side?
I find the priority framework perhaps overspecified at the connection level and underspecified at the message level, with the interaction between the two left explicitly unstated. I would almost rather see the priority type and meaning left completely implementation-specific; otherwise, my suspicion is that someone will write an application using numeric priorities, declare victory when it works fine on one platform, and not understand that the behavior is not universal. In general, I think if TAPS is going to produce a consistent, easily-understandable, and portable API, it needs to stick to easily-understood abstractions. Message-level priority is sort of like the TCP URG mechanism (though better specified and more useful, for sure), but I'm thinking urgent messages sent explicitly out-of-band (e.g., new Connection) with implementation-specific QoS will produce more consistent, predictable, and understandable outcomes in the pessimal case.
Ok for me (and thanks for doing this!)Some nits, but I believe this addresses my concerns in the issue.

Related discussion:
text: will not result in a SendError separate from the InitiateError signaling the failure of Connection establishment. <ins> 8.2.7. The Transport Services interface provides two properties to allow a sender to signal the relative priority of data transmission: the Priority Message Property msg-priority, and the Connection Priority Connection Property conn-priority.  These properties are designed to allow the expression and implementation of a wide variety of approaches to transmission priority in the transport and application layer, including those which do not appear on the wire (affecting only sender-side transmission scheduling) as well as those that do (e.g.  I-D.ietf-httpbis-priority. A Transport Services system gives no guarantees about how its expression of relative priorities will be realized; for example, if a transport stack that only provides a single in-order reliable stream is selected, prioritization information can only be ignored. However, the Transport Services system will seek to ensure that performance of relatively-prioritized connections and messages is not worse with respect to those connections and messages than an equivalent configuration in which all prioritization properties are left at their defaults. The Transport Services interface does order Connection Priority over the Priority Message Property.  In the absense of other externalities (e.g., transport-layer flow control), a priority 1 Message on a priority 0 Connection will be sent before a priority 0 Message on a priority 1 Connection in the same group. </ins> 8.3. Once a Connection is established, it can be used for receiving data