Looks interesting. A few questions/comments: - In what language did you wrote the backend? In particular how do you create the bars/tables? - Wouldn't it be better to just call it something like "Forestpin Flavored Markdown"? From what I get you basically add some extra syntax (like itallics) and extensions (sidenotes) - Regarding the sidenotes, it may be hard to get the syntax. What if you detach it from the location where its mentioned like you do for footnotes?

Anyways, looks pretty cool!