While I was testing book module's conversion to twig, I failed, three times in a row, to actually use book module correctly because the usability is so bad. Each time I tried to create a book page, my workflow was as follows: 1) enter title 2) enter body 3) save. When people follow this workflow (as dictated by the book node page) book nodes fail to be placed in any "book" at all - let alone have any book hierarchy set in the outline.
Placing things in the vertical tabs (or in D8, on the right hand side of the page) tells people that "these things will be set for you by default, and you don't need to think about them when creating content". That was, after all, the whole point of adding vertical tabs in d7 - so that we would have a place to hide stuff.
However, we should not be hiding stuff in vertical tabs that is crucial for functionality.
Additionally, since the vertical tabs functionality that used to let me see what was in those fieldsets has been lost in D8/Seven theme, I had no idea this was happening while I was creating the content. (see)
For enabled content types, the "Book outline" settings need to be moved out of vertical tabs, and in to the main form.
- Move book settings out of vertical tabs
- hide the weight field until a book is selected
- Implement hook_fields_extra_fields to allow the book outline settings to be weighted
User interface changes