Group chapters into "parts" or "books"

[citizenmatt]

I'm sketching out a book that would benefit from grouping chapters, similar to nested articles, but with a top level heading that isn't a numbered chapter, and which resets the numbering after. This is a style I've seen in several text books:

Book I
1. First chapter
2. Second chapter
  2.1. Section inside chapter
3. Third chapter

Book II
1. First chapter
2. Second chapter
  2.1. Section inside chapter
3. Third chapter

The main difference between this and nested chapters/articles is that the "book" title isn't numbered and it resets the numbers for the following articles. I personally wouldn't want to have the book title clickable, either.

Is this something that would be worth doing? I'm happy to have a go at it, but only if it's something that would be accepted.

It could be done by changing the object model - instead of summary just containing a single chapters property, it would have to contain a books property, each of which would have a title and a chapter (and perhaps a link). This would presumably break existing plugins or themes. Is this ok? Or perhaps the chapters property could stay as a backwards compatibility bridge?

Or would it be better implemented in a plugin? Can plugins rewrite the item.level value? In which case, I could get "book" titles without a number and reset the following items easily. But could a plugin remove the not-allowed cursor if it doesn't have a link? Perhaps wrap the top level "book" chapter li in a section?

[citizenmatt]

I've implemented this as a plugin for now. It takes a single list and "promotes" the top level list items to be "part" headers, stripping them of their page number, and stripping the left-most page number from the child list items (e.g. 1.2. becomes 2.)

See citizenmatt/gitbook-plugin-multipart