[Quoth]

Originally Posted by BetterRed

To have the features you want (footnotes, tooltips, margin notes, sidebars etc) I would use a fixed-layout/desktop-publishing editor (e.g. Adobe InDesign, Quark) or a word-processor (Word, LO Writer, WordPerfect) as the starting point and publish the output as a PDF.

Originally Posted by DiapDealer

The Calibre editor certainly supports plugins. Look for the [Editor Plugin] prefix in the Plugin Thread. I've written one myself. Also: https://manual.calibre-ebook.com/cre...t-book-plugins

Yes to both of those.