anchor.diff:  Asciidoctor PDF encodes the content into WINANSI when building the PDF.
   
   WARNING: Built-in (AFM) fonts do not use the <<fallback-fonts,fallback fonts>>.
  -In order for the fallback font to kick in, you must be using a TrueType font.
  +In order for the fallback font to kick in, you must use a TrueType font as the primary font.
   
   .WINANSI Encoding Behavior
   ****
  
positive.code: Now you're covered.
  If your custom TTF font is missing a glyph, Asciidoctor PDF will look in your fallback font.
  You don't need to reference the fallback font anywhere else in your theme file.
  
  == Keys
  
  
negative.code: 
  === Fallback Fonts
  
  If a TrueType font is missing a character needed to render the document, such as a special symbol or emoji, you can have Asciidoctor PDF look for the character in a fallback font.
  
  You only need to specify a single fallback font, typically one that provides a full set of symbols.
  If the character isn't found in the fallback font, it will mostly likely be replaced by a box (i.e., the notdef glyph), which is guaranteed if you're using the bundled fallback font.
  
  IMPORTANT: When defining the fallback font, you *must specify all four variants* (normal, bold, italic, bold_italic), even if you use the same font file for each.
  
  