I'll check this out, thx. I think this project was created just to see what hand coding a lexxer and parser would be like. You know... just for fun. I want to go back afterwards and re-implement it with (f)lex and bison. Probably a good excuse to learn antler as well. I'll check out the tree notation stuff too.
In particular @breck has several that are simpler markdown.
Here is a starting point: https://scroll.pub/