epub heading flow, tag headings flow

[Amontillado]

I'm not sure what these options do in epub export. They are found in the "Spine, TOC & Notes" tab.

The heading flow and tag headings flow seem to be paragraph styles, not auto-flows, and no matter what I select the TOC looks the same.

This could be due to the software I'm using to view the ebook, too (Apple Books).

Just curious and wanting to learn a little. What does heading flow and tag headings flow do?