anchor.diff:  
   renders as:
   
  -[ditaa]
  +[ditaa,_images/ditaa-demo,png]
   ----
       +--------+   +-------+    +-------+
       |        | --+ ditaa +--> |       |
  
positive.code: For example:
  
  ....
  [plantuml,_images/mydiagram,png]
  --
  class Car
  
  
negative.code: 
  renders as:
  
  [graphviz,_images/graphviz-demo,png]
  ----
  digraph automata_0 {
    size ="8.5, 11";
  