anchor.diff:  . `<face>` can be `front` or `back`.
   . The path is resolved relative to base_dir.
   . The target of the image macro is resolved relative to `imagesdir`.
  +. Page background images are automatically scaled to fit within the bounds of the page.
  ++
  +NOTE: Page backgrounds do not currently work when using AsciidoctorJ PDF.
  +This limitation is due to a bug in Prawn 1.3.1.
  +The limitation will remain until AsciidoctorJ PDF upgrades to Prawn 2.x (an upgrade that is waiting on AsciidoctorJ to migrate to JRuby 9000).
  +For more details, see http://discuss.asciidoctor.org/Asciidoctor-YAML-style-file-for-PDF-and-maven-td3849.html[this thread].
   . Controls whether the `page-number` attribute is accessible to the running header and footer content specified in the theme file.
   Use the `noheader` and `nofooter` attributes to disable the running header and footer, respectively, from the document.
   . Enables generation of the http://milan.kupcevic.net/ghostscript-ps-pdf/#marks[pdfmark] file, which contains metadata that is fed to Ghostscript when optimizing the PDF file.
  
positive.code: |screen {vbar} print {vbar} prepress
  |:media: prepress
  
  |page-background-image
  |path^[2]^ {vbar} image macro^[3]^
  |+:page-background-image: image:bg.jpg[]+
  
  |pagenums^[4]^
  |flag (default: _set_)
  |:pagenums:
  
  
negative.code: |https://github.com/prawnpdf/pdf-core/blob/0.6.0/lib/pdf/core/page_geometry.rb#L16-L68[Named size^] {vbar} <<measurement-units,Measurement[width, height]>>
  |:pdf-page-size: 6in x 9in
  
  |pdfmark^[6]^
  |flag (default: _not set_)
  |:pdfmark:
  
  |text-alignment^[7]^
  |<<text-alignments,Text alignment>>
  |:text-alignment: left
  
  