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?