docs: protected void recursiveExtractInstances(Area root, Instances dest)
      {
          Instance newinst = features.getAreaFeatures(root, dest);
          
          String cls = defaultClass;
          for (Tag tag : root.getTags().keySet())
          {
              if (tag.getType().equals(tagType))
                  cls = tag.getValue();
          }
          newinst.setClassValue(cls);
          dest.add(newinst);
          
          for (int i = 0; i < root.getChildCount(); i++)
              recursiveExtractInstances(root.getChildAt(i), dest);
      }