anchor.diff:      (:edge attribute)
       (:ranksep float)
       (:ordering (:out))
  -    (:rankdir ("LR" "RL" "BT"))
  +    (:rankdir ("LR" "RL" "BT" "TB"))
       (:dir ("forward" "none"))
       (:pagedir text)
       (:layout text) ;; neato, twopi, etc.
  
positive.code:     (:tooltip text)
      (:id text)))
  
  (defparameter *edge-attributes*
    '((:minlen integer)
      (:weight integer)
      (:arrowhead ("normal" "inv" "dot" "invdot" "odot" "invodot" "none" "tee" "empty" "invempty" "diamond" "odiamond" "ediamond" "crow" "box" "obox" "open" "halfopen" "vee" "circle"))
      (:label label-text)
      (:fontsize integer)
      (:fontname text)
  
negative.code:     (:dir (:forward :back :both :none))
      (:tailclip boolean)
      (:headclip boolean)
      (:arrowhead ,*predefined-arrow-shapes*)
      (:arrowtail ,*predefined-arrow-shapes*)
      (:headlabel label-text)
      (:taillabel label-text)
      (:ltail text)
      (:lhead text)
      (:labelfontsize integer)
      (:labelfontname text)
      (:labelfontcolor text)
  