You can write filters in Python and several other languages. These let you perform arbitrary computation triggered by tags in your source document, and let you extend Pandoc’s Markdown to include your own custom tags to do anything you can imagine.

Here is an article where I show how to use Panflute, a library that lets you write filters in Python, and how I wrote a set of filters to automate the tedious parts of writing a complex technical manual:

https://lee-phillips.org/panflute-gnuplot/