* @param elementsToRetain the elements to retain
   * @return {@code true} if any element was removed from {@code iterator}
   */
  @CanIgnoreReturnValue
  public static boolean retainAll(Iterator<?> removeFrom, Collection<?> elementsToRetain) {
    checkNotNull(elementsToRetain);
    boolean result = false;
    while (removeFrom.hasNext()) {
      if (!elementsToRetain.contains(removeFrom.next())) {

    SortedSet<String> subset = elementSet.subSet("b", "f");
    assertThat(subset).containsExactly("b", "c", "d", "e").inOrder();

    assertTrue(subset.retainAll(asList("a", "c")));
    assertThat(elementSet).containsExactly("a", "c", "f").inOrder();
    assertThat(subset).containsExactly("c");
    assertEquals(5, ms.size());
  }

  public void testElementSetSubsetClear() {

    assertThrows(UnsupportedOperationException.class, () -> values.removeAll(singleton("four")));
    assertThrows(UnsupportedOperationException.class, () -> values.retainAll(singleton("four")));
    assertThrows(
        UnsupportedOperationException.class,
        () -> {
          Iterator<String> iterator = values.iterator();
          iterator.next();

	if !ok {
		tillStr, ok = meta[AmzObjectLockRetainUntilDate]
	}
	if ok {
		if t, e := amztime.ISO8601Parse(tillStr); e == nil {
			retainTill = RetentionDate{t.UTC()}
		}
	}
	return ObjectRetention{XMLNS: "http://s3.amazonaws.com/doc/2006-03-01/", Mode: mode, RetainUntilDate: retainTill}
}

// GetObjectLegalHoldMeta constructs ObjectLegalHold from metadata
func GetObjectLegalHoldMeta(meta map[string]string) ObjectLegalHold {