The old book format allowed articles to be organised into Chapters. The current Book Creator tool provides an interactive GUI for doing this: https://en.wikipedia.org/wiki/Special:Book
The current PediaPress print-on-demand book tool for Wikipedia books on their own web site also supports Chapters.
Yet we are told that chapters will not be implemented in the forthcoming Wikipedia PDF builder from PediaPress.
I believe that this is a grave mistake, as it will bork a great many existing books, users accustomed to downloading books in the old format will become very confused, and the Book Creator will need rewriting to remove the feature.
I do not believe that a tool which plays so badly with the legacy base should be rolled out live, I believe very strongly that this feature should be reinstated before the new PDF tool goes live on Wikipedia.