## Scope and purpose

Add a few words about why this PR is needed and what is its scope.

Add mentions of things that are not covered here and are planed to be done
in separate PRs.


## Remove this section

Please have a look at [our developer documentation](https://twistedmatrix.com/trac/wiki/TwistedDevelopment#SubmittingaPatch) before submitting your Pull Request.

Please note that the trac ticket, news fragment, and review submission portions of this process apply to *all* pull requests, no matter how small; if you don't do them, it's likely that nobody will even notice your PR needs a review.


## Contributor Checklist:

* [ ] The associated ticket in Trac is here: https://twistedmatrix.com/trac/ticket/<!-- Create a new one at https://twistedmatrix.com/trac/newticket and replace this comment with the ticket number. -->
* [ ] I ran `tox -e lint` to format my patch to meet the [Twisted Coding Standard](https://twistedmatrix.com/documents/current/core/development/policy/coding-standard.html)
* [ ] I have created a newsfragment in src/twisted/newsfragments/ (see: [News files](https://twistedmatrix.com/trac/wiki/ReviewProcess#Newsfiles))
* [ ] I have updated the automated tests.
* [ ] I have submitted the associated Trac ticket for review by adding the word `review` to the keywords field in Trac, and putting a link to this PR in the comment; it shows up in https://twisted.reviews/ now.
