anchor.diff:  |Populates the content language / locale (`<dc:language>`) in the package metadata.
   
   |scripts
  -|Controls the font subsets that are selected based on the specified scripts (e.g., alphabets). (values: *latin*, latin-ext, latin-cyrillic or multilingual)
  +|Controls the font subsets that are selected based on the specified scripts (e.g., alphabets).
  +(values: *latin*, latin-ext, latin-cyrillic or multilingual)
   
   |revdate
   |Populates the publication date (`<dc:date>`) in the package metadata.
  
positive.code: \ifndef::ebook-format[:leveloffset: -1]
  ----
  
  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]).
  
  NOTE: Eventually, we envision introducing a dedicated block macro to represent a spine item so that we don't overload the meaning of the include directive.
  However, for the time being, the include directive fills this role.
  
negative.code: 
  |username
  |Used to resolve an avatar for the author that is displayed in the header of a chapter.
  The avatar image should be located at the path _\{imagesdir}/avatars/\{username}.jpg_, where `\{username}` is the value of this attribute.
  
  |producer
  |Populates the publisher (`<dc:publisher>`) in the package metadata.
  