anchor.diff:  
   ////
   Topics remaining to document:
  -* transparent color
  -* additional fonts provided by Asciidoctor PDF
  -* images
  -* title page layout
  -* title image
  -* title page background image
  -* keys
  -* how to apply the theme
  +* line height and line height length (and what that all means)
  +* title page layout / title page images (logo & background)
  +* document that unicode escape sequences can be used inside double-quoted strings
   ////
   
   The theming system in Asciidoctor PDF is used to control the layout and styling of the PDF file that Asciidoctor PDF generates from AsciiDoc.
  
positive.code: 
  === Images
  
  PENDING
  
  == Fonts
  
  You can select from built-in PDF fonts or custom fonts loaded from TrueType font (TTF) files.
  If you want to use custom fonts, you must first declare them in your theme file.
  
  === Built-in fonts
  
negative.code:   margin: [0.75in, 1in, 0.75in, 1in]
  ----
  
  The order of elements in a measurement array is the same as it is in CSS:
  
  . top
  . right
  . bottom
  . left
  
  === Colors
  
  The theme language supports color values in three formats:
  