From the documentation:

https://docs.python.org/3/c-api/stable.html

    In the C API documentation, API elements that are not part of the limited API are marked as "Not part of the limited API."

But they don't.

Following sample patch adds the notes to Unicode Objects and Codecs C API. I'm going to add them to all C API.

What are your though about formatting the note? Should it be before the description, after the description, but before the "deprecated" directive (as in the patch), or after the first paragraph of the description? Should it be on the separate line or be appended at the end of the previous paragraph, or starts the first paragraph (if before the description)? May be introduce a special directive for it?

I have found that there is an option :stableabi: for C API elements. But it is not used in the documentation. Shouldn't we start to use it?

The bigger problem is that currently, it's not clear what is limited API and what is not.

I am working to propose a PEP to fix this. It will also cover documentation: https://discuss.python.org/t/pre-pep-maintaining-the-stable-abi/6986

PEP 652 is currently draft & it's discussed at https://discuss.python.org/t/pep-652-maintaining-the-stable-abi/6986

PEP 652 is now in, and with it a list of everything that *is* in the stable ABI: https://docs.python.org/3.10/c-api/stable.html#contents-of-limited-api

I'm closing the issue.