That's cool. I'll have to read up on EPUB3—I'm not familiar with it.

(I worked on iBooks for the Mac like 15 years ago—it's where I got to dive into the ePub format. A lot has changed in the standard since I am sure.)

EDIT: looks like EPUB3 has a "paginated" mode as well as more sophisticated layout tags.

Also appears to have support for ruby and vertical writing modes. This was not yet supported in WebKit when I worked on iBooks. Somehow, this white guy from Kansas (who knows no language other than English) got tapped to implement the vertical TOC for Asian languages. Also tasked with annotating the ePUB pages to display (also vertical) ruby text…