anchor.diff:    - separate running content for chapter page (by default uses normal content)
   * should we rename base_ to body_ to make it more familiar to CSS developers?
   * support !include in theme file (file issue)
  -* margin per heading level (see https://github.com/asciidoctor/asciidoctor-pdf/issues/176)
   * add cover page example to chronicles so people see how to use it
   * don't orphan a single line of paragraph (send it with a buddy line)
   * implement stem support
  
positive.code: 
  == TODO
  
  * convert "-" in variable name in theme to underscore (e.g., $base-font-size)
  * apply calculated theme values after loading?
  * allow "content" in place of recto_content & verso_content for running header/footer
  * allow image to span width of page (role=canvas, role=canvas-x or role=canvas-y); if role is canvas or canvas-y, then it does not consume height
  
negative.code: * https://code.google.com/p/origami-pdf/[Origami PDF: A PDF inspection library]
  * https://github.com/a1ee9b/PrintPretty[A theme for PDF designed for printing]
  * http://randomtextgenerator.com[Random Text Generator, supports multiple languages]
  * http://clagnut.com/blog/2380[List of pangrams]
    - http://www.camcc.org/_media/reading-group/qianziwen-en.pdf[1,000 character classic (Chinese)]
  