After reading all my learned colleagues' opinions I can only offer this Fool's thoughts.

It's simple. 100 page book, you can't use more than 10 pages. If the book is divided into chapters those 10 pages cannot come from more than one chapter.

But it could use a that here:

in a case where the work is divided into chapters that exceed, in the aggregate, 10% of the number of pages in that edition…