code: final Selector append(Selector s) {
  		if (this.next == null) {
  			return this.copy(s);
  		} else {
  			return this.copy(this.next.append(s));
  		}
  	}
docs: Note: prepending should simply be done by passing a chain at first
  selector's instantiation. Appends the given selector at the end of
  current list, and returns new list's head