WP_HTML_Processor::step_in_cell()'s 6.9.1 documentation (source here) is an example of a private method that is documented publicly.
Its public documentation contains this notice:
This function’s access is marked private. This means it is not intended for use by plugin or theme developers, only in other core functions. It is listed here for completeness. Use https://html.spec.whatwg.org/#parsing-main-intd instead.
It suggests an alternative, which was not intended in this case.
It appears that a private method will suggest the first @see tag as an appropriate alternative.
This is surprising behavior and may not be appropriate. It should be reviewed and perhaps disabled.