anchor.diff:  |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^[5]^
  +|pdfmark^[6]^
   |flag (default: _not set_)
   |:pdfmark:
   
  -|text-alignment^[6]^
  +|text-alignment^[7]^
   |<<text-alignments,Text alignment>>
   |:text-alignment: left
   
  
positive.code: . `<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`.
  . 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.
  
negative.code: |screen {vbar} print {vbar} prepress
  |:media: prepress
  
  |page-background-image^[4]^
  |path^[2]^ {vbar} image macro^[3]^
  |+:page-background-image: image:bg.jpg[]+
  
  |pagenums^[5]^
  |flag (default: _set_)
  |:pagenums:
  
  