https://github.com/jgm/peg-markdown https://github.com/jgm/peg-markdown and https://github.com/fletcher/peg-multimarkdown https://github.com/fletcher/peg-multim

https://github.com/jgm/peg-markdown https://github.com/jgm/peg-markdown and https://github.com/fletcher/peg-multimarkdown https://github.com/fletcher/peg-multimarkdown I haven't looked at the implementations of these, but they are most certainly grammar-based, not regex-based.