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Addresses #2236 and does not touch files that are addressed in #5057

That's just a tiny fraction of the module - and a private bit of the API too - did you do more but forgot to push the work to GitHub?

I thought smaller PRs would make it easier to review and accept.

For type annotation, please do at least a whole file. Or most of it.

OK. I have made some progress. This still needs more work.