anchor.diff:  
   |font_size^[1]^
   |<<values,Number>> +
  -(default: h1=24; h2=18; h3=16; h4=14; h5=12; h6=10)
  +(default: <1>=24; <2>=18; <3>=16; <4>=14; <5>=12; <6>=10)
   |heading:
     h6_font_size: $base_font_size * 1.7
   
  
positive.code: If content is not specified for the running footer, the page number (i.e., `\{page-number}`) is shown on the left on verso pages and the right on recto pages.
  You can disable this behavior by defining the attribute `nofooter` in the AsciiDoc document header or by defining the key `footer_<side>_content: none` in the theme.
  
  TIP: Although not listed in the table above, you can control the font settings used for running content for each column position on each page side (e.g., `footer_<side>_<position>_font_color`).
  For example, you can set the font color used for the right-hand column on recto pages by setting `footer_recto_right_font_color: 6CC644`.
  
  ==== Attribute References
  
negative.code: |base:
    font_size: 10.5
  
  // font_size_large is a variable, not an official key
  //|font_size_large
  //|<<values,Number>>
  //|base:
  //  font_size_large: 13
  
  |font_size_min
  |<<values,Number>> +
  (default: 9)
  |base:
    font_size_min: 6
  
  // font_size_small is a variable, not an official key
  //|font_size_small
  //|<<values,Number>>
  //|base:
  //  font_size_small: 9
  
  |font_style
  |<<font-styles,Font style>> +
  