code: private boolean add_i(final GroupElement e) {
  	if (e == null || e == this) {
  	    // -DEBUG
  	    System.out.println("Group::add_i::failed to add " + e.get_name() + " (null or self)");
  	    return false;
  	}
  	final GroupElement ge = find_i(e.get_name(), e instanceof Group ? false : true);
  	if (ge != null && ge != this) {
  	    // -DEBUG
  	    System.out.println("Group::add_i::failed to add " + e.get_name() + " (already attached)");
  	    return false;
  	}
  	elements.add(e);
  	e.set_parent(this);
  	return true;
      }
docs: Adds an element to the group