Buttondown's core WYSIWYG editor is built on top of Tiptap, a headless wrapper around ProseMirror that removes much of the busywork and trickiness in building a lovely, feature-rich writing experience.

Tiptap comes with a lot of great extensions out of the box for common bits of functionality like headings, but for the more esoteric stuff they expose a pretty solid Extensions API so you can build out your own blocks. We built out our own extension for footnotes a few weeks ago, and have now open-sourced it so any developer trying to add footnotes doesn't have to re-invent the wheel.

It's called tiptap-footnotes (admittedly, not the most creative name in the world) and you can install it right now:

Or, if you're so interested, play around with it on CodeSandbox.

A huge thank you to the Tiptap team for building such a solid, extendible framework! (And if you're interested, check out the rest of our open source packages here.)