Remove the book attribute in responses because it is never returned by the API. Currently, Chapters Create does not return book_slug! (The example response is consistent with the inconsistent API behavior)
- Fixed page editor default focus not working as expected due to
misnamed attribute.
- Added owned_by to relevant areas of the API including the docs.
- Made book relation on page accessible even if deleted since it could cause an issue on views, such as audit trail, when the relation is accessed when the book is deleted.
