You know how you can write notes in an Kindle book? That seems to be Amazon’s propietary system for recording notes. Especially since Amazon doesn’t even use ePub files in the first place (they use mobi files).
It would be cool if there was a way to publish a Kindle book with notes already in it. And if not a Kindle book, then I would like to see a way of publishing an ePub file with notes.
Ten years later, I find myself asking the same question: Is there a standard ePub format for notes?
Looks like hypothes.is might have a solution: https://web.hypothes.is/demos/epubjs/