anchor.diff:  
   \include::chapter-three.adoc[]
   ----
  +
  +Here's an example showing the structure of a chapter document:
  +
  +----
  +[#chapter-one]
  += Chapter One
  +
  +chapter content
  +----
  +
  +Although an explicit ID is not necessary over the chapter title, it is recommended.
   
   If the master document does not contain any include directives, then the converter treats the document as the sole chapter in the EPUB3 archive and automatically produces a navigation file that references it. (Currently broken. See issue https://github.com/asciidoctor/asciidoctor-epub3/issues/47[#47]).
   
  
positive.code: === Declaring the Spine
  
  Asciidoctor relies on top-level include directives (i.e., include directives in the master document) to indicate where the chapter splits should occur.
  In other words, you must be explicit.
  Asciidoctor will not try to guess.
  If your AsciiDoc document is not structured in this way, you'll need to change it to use the {project-name} converter properly.
  
negative.code: :doctype: book
  :imagesdir: images
  //...and so on
  \ifndef::ebook-format[:leveloffset: 1]
  
  \include::chapter-one.adoc[]
  
  