Change numbering styles in different parts

Describe the problem/need and solution

Sphinx allows you to add numbers to chapters via the :numbered: flag in a TOCtree. In addition, sphinx-multitoc-numbering allows you to continue numbering across parts.

However, many books have an appendix that should both restart numbering and use a different numbering style. A common example of this is:

Introduction

1. First chapter
2. Second chapter
3. Third chapter

A. Appendix 1
B. Appendix 2

It would be useful if people could do two things:

1. Re-start numbering for some parts of their book
2. Choose a different numbering style

Guide for implementation

There’s a Sphinx issue that already exists about this: https://github.com/sphinx-doc/sphinx/issues/6614

But perhaps we could implement something via sphinx-multitoc-numbering, for example supporting some extra toctree metadata like:

```{toctree}
:numbered:
:numbered_group:
```

Along with a config like numbered_group_styles = {"group1": "123", "group2": "ABC"}.

I wonder if @mmcky has thought about that possibility?

Tasks and updates

No response

[tavin]

Thanks to https://github.com/executablebooks/MyST-Parser/issues/188 I found a workaround that allows me to build a latex/pdf article with appendix numbered A:

```{role} raw-latex(raw)
:format: latex
```

{raw-latex}`\renewcommand{\thesection}{A}`

I’d like to do this with a raw directive and skip the role definition, but for some reason that doesn’t work.

[michaelosthege]

This week I managed to render a pandoc-Markdown into DOCX and PDF that look really good. For the PDF I even got partially numbered headings working: https://boisgera.github.io/pandoc/markdown/#heading-identifiers

Maybe one can adopt their approach?

---

Are there examples (tests?) where _toc.yml is bypassed? I looked into the code and it seems to be mostly a big codebase parsing the YAML and making a dict of objects from it. I’d much rather create those TocTree objects myself, interacting with their API directly and having access to attributes that are not supported in the _toc.yml “schema”. (Such as the numbered/unnumbered thing.)