public void push(Element element) {
        stack.getFirst().appendChild(element);
        stack.addFirst(element);
    }

    public Element pop() {
        Element element = stack.removeFirst();
        if (emptyPara(element)) {
            element.getParentNode().removeChild(element);
        }
        return element;
    }

    private boolean emptyPara(Element element) {

/**
 * An {@code Iterable} whose elements are sorted relative to a {@code Comparator}, typically
 * provided at creation time.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
interface SortedIterable<T extends @Nullable Object> extends Iterable<T> {
  /**
   * Returns the {@code Comparator} by which the elements of this iterable are ordered, or {@code
   * Ordering.natural()} if the elements are ordered by their natural ordering.
   */

/**
 * An {@code Iterable} whose elements are sorted relative to a {@code Comparator}, typically
 * provided at creation time.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
interface SortedIterable<T extends @Nullable Object> extends Iterable<T> {
  /**
   * Returns the {@code Comparator} by which the elements of this iterable are ordered, or {@code
   * Ordering.natural()} if the elements are ordered by their natural ordering.
   */

                new TestStringSetGenerator() {
                  @Override
                  protected Set<String> create(String[] elements) {
                    return new StandardImplForwardingNavigableSet<>(
                        new SafeTreeSet<String>(asList(elements)));
                  }

                  @Override
                  public List<String> order(List<String> insertionOrder) {

  // Query Operations

  /**
   * Returns the number of occurrences of {@code element} in this multiset.
   *
   * @param element the element to look for
   * @return the nonnegative number of occurrences of the element
   */
  @Override
  public int count(@Nullable Object element) {
    AtomicInteger existingCounter = safeGet(countMap, element);
    return (existingCounter == null) ? 0 : existingCounter.get();
  }

  public void testHashCode_containingNull() {
    Collection<E> elements = getSampleElements(getNumElements() - 1);
    int expectedHashCode = 0;
    for (E element : elements) {
      expectedHashCode += (element == null) ? 0 : element.hashCode();
    }

    elements.add(null);
    collection = getSubjectGenerator().create(elements.toArray());
    assertEquals(

    assertEquals("Should have removed an element", 2, list.size());
    assertFalse("Second element should be gone", list.contains("B"));
  }

  static class ThrowsAtEndException extends RuntimeException {
    /* nothing */
  }

  /**
   * This Iterator claims to have more elements than the underlying iterable, but when you try to
   * fetch the extra elements, it throws an unchecked exception.
   */

   * Creates a new {@code EnumMultiset} containing the specified elements.
   *
   * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
   *
   * @param elements the elements that the multiset should contain
   * @throws IllegalArgumentException if {@code elements} is empty
   */
  public static <E extends Enum<E>> EnumMultiset<E> create(Iterable<E> elements) {
    Iterator<E> iterator = elements.iterator();

 *   <li>{@code merge} (default): Merges elements with matching names</li>
 *   <li>{@code append}: Adds elements as siblings</li>
 * </ul>
 *
 * <p>Self combination modes (specified by {@code combine.self} attribute):</p>
 * <ul>
 *   <li>{@code merge} (default): Merges attributes and values</li>
 *   <li>{@code override}: Completely replaces the element</li>
 *   <li>{@code remove}: Removes the element</li>
 * </ul>
 *

        this.parent = parent
    }

    protected Element createNode(Object name) {
        Element element = document.createElement(name as String)
        if (getCurrent() == null) {
            elements << element
            parent?.appendChild(element)
        }
        return element
    }

    protected Element createNode(Object name, Map attributes) {
        Element element = createNode(name)
        attributes.each {key, value ->