Quark release a new manual called “Digital Publishing with QuarkXPress 2016”.
It can be found here and describes how to create app content for native apps, ebooks in the EPUB2 and EPUB3 format (reflow and fixed-layout) and HTML5 Publications:
Both an engineer and a layout artist, Matthias bridges the gap between technology and people. Before joining Quark in 1997, Matthias pioneered print, Web, and multimedia products for multiple German publishing companies. He is an active participant in design and publishing communities and represented Quark in the Ghent PDF Workgroup.
From 1997 until 2019 Matthias played a central role in shaping Quark’s desktop, mobile and enterprise software. From February 2014 until January 2019 he headed Quark’s Desktop Publishing business unit; and was therefore responsible for QuarkXPress.
Matthias does not work for Quark anymore. If you want to connect with him, please visit his LinkedIn profile on https://www.linkedin.com/in/mguenther/