title_body: Do epub 3.0 pagebreaks always require an id?
upvoted_answer: Pagebreaks are usually used in conjunction with nav document page-list sections and since you need an id to refer to pagebreak markers in the book it'd be rather pointless to use pagebreaks without ids and a corresponding page-list section.
  
  You can find an IDPF-approved sample epub3 book with pagebreaks and a page-list nav section here.