anchor.diff:  |header:
     image-vertical-align: 4
   
  -|sectlevels
  +|sectlevels^[4]^
   |Integer +
   (default: 2)
   |header:
  
positive.code: |header:
    vertical-align: center
  
  |<side>-columns^[4]^
  |Column specs triple +
  (default: _not set_)
  |header:
    recto:
      columns: <25% =50% >25%
  
  |<side>-<position>-content^[4,5]^
  |<<quoted-string,Quoted string>> +
  (default: '\{page-number}')
  |header:
  
negative.code: |footer:
    vertical-align: top
  
  |<side>-columns^[5]^
  |Column specs triple +
  (default: _not set_)
  |footer:
    verso:
      columns: <50% =0% <50%
  
  |<side>-<position>-content^[5,6]^
  |<<quoted-string,Quoted string>> +
  (default: '\{page-number}')
  |footer:
  