Chapter-processed books should have same "part" functionality
Originally NCBI's brief included different use cases for adding parts in the PDF and XML workflow, and we partially developed that in #401 (closed) with the understanding that user would not submit content to the same book by FTP and via the UI. However, since then that use case has changed (#475 (comment 58180))
In this initial release, parts will only be supported by adding them in the UI bu the "add part", as currently developed for Word and PDF workflow.
This should be the same for XML workflow. You can see in this book, when I create a book that supports parts, the "add part" button ; "move to" ; and "Preview TOC" button don't display.
The variation of creating a part by file upload is still valid in the PDF and XML workflow but supporting this will only be scoped after the initial release.