public <F extends Content> List<F> removeContent(Filter<F> filter) {
    List<F> old = new ArrayList<>();
    Iterator<F> iter = content.getView(AbstractFilter.toFilter2(filter)).iterator();
    while (iter.hasNext()) {
      F child = iter.next();
      old.add(child);
      iter.remove();
    }
    return old;
  }
public <F extends Content> List<F> removeContent(Filter<F> filter)