@Override
   public int getIndex(TreeNode arg0) {
      if (arg0 instanceof Section) {
         Section soo = (Section) arg0;
         for (int i = 0; i < this.sectionCount(); i++) {
            if (this.getSection(i).equals(soo))
               return i;
         }
         return -1;
      } else if (arg0 instanceof Property) {
         Property poo = (Property) arg0;
         for (int j = 0; j < this.propertyCount(); j++) {
            if (this.getProperty(j).equals(poo))
               return (j + this.sectionCount());
         }
         return -1;
      } else {
         logger.error("!should not happen as TreeNode can only be Section or Property! "
               + "Here we have: "
               + arg0.getClass());
         return -1;
      }
   }