anchor.diff:  |footer:
     line_height: 1.2
   
  -|padding
  +|padding^[3]^
   |<<measurement-units,Measurement>> {vbar} <<measurement-units,Measurement[top,right,bottom,left]>> +
   (default: 0)
   |footer:
  
positive.code: |header:
    line_height: 1.2
  
  |padding
  |<<measurement-units,Measurement>> {vbar} <<measurement-units,Measurement[top,right,bottom,left]>> +
  (default: 0)
  |header:
  
negative.code: |footer:
    vertical_align: top
  
  |<side>_columns^[4]^
  |Column specs triple +
  (default: _not set_)
  |footer:
    verso:
      columns: <50% =0% <50%
  
  |<side>_<position>_content^[4,5]^
  |<<quoted-string,Quoted string>> +
  (default: '\{page-number}')
  |footer:
  