Change:
1.1. <del> The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this document.  It's not shouting; when these words are capitalized, they have a special meaning as defined in RFC2119. </del> <ins> The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 RFC2119 RFC8174 when, and only when, they appear in all capitals, as shown here. </ins> 2. <del> QUIC uses UDP as a substrate for userspace implementation and port numbers for NAT and middlebox traversal.  While there is no evidence of widespread, systematic disadvantage of UDP traffic compared to TCP in the Internet Edeline16, somewhere between three Trammell16 and five Swett16 percent of networks simply block UDP traffic.  All applications running on top of QUIC must therefore either be prepared to accept connectivity failure on such networks, or be engineered to fall back to some other transport protocol.  This fallback SHOULD provide TLS 1.3 or equivalent cryptographic protection, if available, in order to keep fallback from being exploited as a downgrade attack. In the case of HTTP, this fallback is TLS 1.3 over TCP. </del> <ins> QUIC uses UDP as a substrate.  This enables both userspace implementation traversal of middleboxes and NAT without requiring updates. While there is no evidence of widespread, systematic disadvantage of UDP traffic compared to TCP in the Internet Edeline16, somewhere between three Trammell16 and five Swett16 percent of networks simply block UDP traffic.  All applications running on top of QUIC must therefore either be prepared to accept connectivity failure on such networks, or be engineered to fall back to some other transport protocol.  In the case of HTTP, this fallback is TLS 1.3 over TCP. An application that implements fallback needs to consider the security consequences.  A fallback to TCP and TLS 1.3 exposes control information to modification and manipulation in the network.  Further downgrades to older TLS versions might result in significantly weaker cryptographic protection.  For example, the results of protocol negotiation ALPN only have confidentiality protection if TLS 1.3 is used. </ins> These applications must operate, perhaps with impaired functionality, in the absence of features provided by QUIC not present in the

Discussion:
These are pretty big. If you would prefer that I create a PR for each individual commit, that can be done. It turns out that there were a lot of things I found needed work. For instance, this completely redoes the 0-RTT advice.
It did kinda snowball, for which I apologize. I was trying to get something under your nose before I got swamped by meetings. I am also on vacation next week. I'm reading through and there is some really good stuff in the doc. I have started to open issues where I don't think the fixes are so simple.
Aside from the keep-alive tweak and the idempotence change, these are all editorial and LGTM, thanks! The keepalive tweak is also good. Having looked at URL, the text here is a good applicability-appropriate view on what's there now. assuming discussion there converges to mostly the same thing, I'd be happy to merge this. (in the future, no need to make tiny PRs, but splitting into "editorial-rollup" and "substantive editorial changes" would be nice to separate discussion, since the former shouldn't need much of it)Changes look all ready good. Thanks! I just have left one minor comment/question to double-check before we merge.