[patrickmeenan]

FWIW, this addresses the BREACH/CRIME issues that killed SDCH by only operating on CORS-readable content.

It also solves the problem that SDCH had where the dictionary would be forced on the response and the client would have to go fetch it if it didn't have it before it could process the response.

The tooling for generating dictionaries is also WAY better than it was back in the SDCH days (and they are a much cleaner format, being arbitrary byte strings that Brotli and ZStandard can back-reference).

Lots of people involved in working on it were also involved with SDCH and have been trying to find a workable solution since it had to be turned down.