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: 
  |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.
  
negative.code: Images that your AsciiDoc document references should be saved in the directory defined in the `imagesdir` attribute, which defaults to the directory of the document.
  {project-name} will discover all local image references and insert the images into the EPUB3 archive at the same relative path.
  
  WARNING: Currently including images only works correctly if you set `imagesdir` to the directory `images` like in the example shown above.
  This will be fixed in future versions.
  
  The sample book contains placeholder images for an author avatar and a book cover.
  
  