anchor.diff:  3+|*Key Prefix:* header
   
   |background_color^[1]^
  -|<<colors,Color>>
  +|<<colors,Color>> +
  +(default: _not set_)
   |header:
     background_color: #eeeeee
   
   |border_color
  -|<<colors,Color>>
  +|<<colors,Color>> +
  +(default: _not set_)
   |header:
     border_color: #dddddd
   
  
positive.code:   border_style: dashed
  
  |border_width
  |<<measurement-units,Measurement>>
  |footer:
    border_width: 0.25
  
  |font_color
  |<<colors,Color>>
  |footer:
    font_color: #333333
  
  |font_family
  |<<fonts,Font family name>>
  |footer:
    font_family: Noto Serif
  
  |font_size
  |<<values,Number>>
  |footer:
    font_size: 9
  
  |font_style
  |<<font-styles,Font style>>
  |footer:
    font_style: italic
  
  |height
  |<<measurement-units,Measurement>>
  |footer:
    height: 0.75in
  
  
negative.code:   line_height: 1.2
  
  |padding
  |<<measurement-units,Measurement>> {vbar} <<measurement-units,Measurement[top,right,bottom,left]>> +
  (default: 0)
  |header:
    padding: [0, 3, 0, 3]
  
  |image_vertical_align
  |top {vbar} middle {vbar} bottom {vbar} <<measurement-units,Measurement>> +
  (default: _not set_)
  |header:
    image_vertical_align: 4
  
  |vertical_align
  |top {vbar} middle {vbar} bottom +
  (default: middle)
  |header:
    vertical_align: center
  
  |<side>_columns^[3]^
  |Column specs triple +
  (default: _not set_)
  |header:
    recto:
      columns: <25% =50% >25%
  
  |<side>_<position>_content^[3,4]^
  |Quoted string
  |header:
    recto:
  