anchor.diff:     (horizontal-scroll-distance
       50
       :type integer
  -    :documentation "Horizontal scroll distance. The
  -distance scroll-left or scroll-right will scroll.")
  +    :documentation "Horizontal scroll distance. The distance scroll-left or
  +scroll-right will scroll.")
      (current-zoom-ratio
       1.0
       :type float
  
positive.code: (define-class document-buffer (buffer)
    ((document-model-delta-threshold
      10
      :documentation "Update the document model when the amount of elements on the
      page change greater than this amount."
      :export nil)
     (document-model
      nil
  
negative.code:    (download-engine
      :initform :renderer
      :type symbol
      :documentation "Select a download engine to use, such as `:lisp' or
  `:renderer'.")
     (history-file
      (make-instance 'history-file)
      :type history-file
  