[atomicnature]

For extending markdown capabilities, there are many plugins/filters. Example [1].

I remember using extensions/filters for citations, etc.

Ultimately it is just some custom tooling around pandoc; so whatever you can do in pandoc, you can get done in the book.

[1] - https://github.com/chdemko/pandoc-latex-admonition

[2] - https://pandoc.org/