class Fragment implements Iterable<Atom> {

	void addAtom(Atom atom) {
		List<String> locants =atom.getLocants();
		for (String locant: locants) {
			atomMapFromLocant.put(locant, atom);
		}
		atomMapFromId.put(atom.getID(), atom);
		atom.setFrag(this);
	}

	  Fragment(Element tokenEl);
	  Fragment(String type);

}