anchor.diff:  |<face>-cover-image^[1]^
   |path^[2]^ {vbar} image macro^[3]^ +
   (format can be image or PDF)
  -|+:front-cover-image: image:front-cover.pdf[]+
  +|:front-cover-image: image:front-cover.pdf[]
   
   |media
   |screen {vbar} print {vbar} prepress
  
positive.code: |Inline image macro^[2]^ +
  (default: _not set_)
  |page:
    background_image: +image:page-bg.png[]+
  
  |layout
  |portrait {vbar} landscape +
  
negative.code: 
  |page-background-image^[4]^
  |path^[2]^ {vbar} image macro^[3]^
  |:page-background-image: image:bg.jpg[]
  
  |pagenums^[5]^
  |flag (default: _set_)
  