/*
    * Copyright (c) 2002-2025 Gargoyle Software Inc.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    * https://www.apache.org/licenses/LICENSE-2.0
    *
    * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.htmlunit.html;
  
  import java.io.IOException;
  import java.io.PrintWriter;
  import java.io.Serializable;
  import java.io.StringWriter;
  import java.nio.charset.Charset;
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.NoSuchElementException;
  
  import org.htmlunit.BrowserVersionFeatures;
  import org.htmlunit.IncorrectnessListener;
  import org.htmlunit.Page;
  import org.htmlunit.SgmlPage;
  import org.htmlunit.WebAssert;
  import org.htmlunit.WebClient;
  import org.htmlunit.WebClient.PooledCSS3Parser;
  import org.htmlunit.WebWindow;
  import org.htmlunit.css.ComputedCssStyleDeclaration;
  import org.htmlunit.css.CssStyleSheet;
  import org.htmlunit.css.StyleAttributes;
  import org.htmlunit.cssparser.parser.CSSErrorHandler;
  import org.htmlunit.cssparser.parser.CSSException;
  import org.htmlunit.cssparser.parser.CSSOMParser;
  import org.htmlunit.cssparser.parser.CSSParseException;
  import org.htmlunit.cssparser.parser.selector.Selector;
  import org.htmlunit.cssparser.parser.selector.SelectorList;
  import org.htmlunit.html.HtmlElement.DisplayStyle;
  import org.htmlunit.html.serializer.HtmlSerializerNormalizedText;
  import org.htmlunit.html.serializer.HtmlSerializerVisibleText;
  import org.htmlunit.html.xpath.XPathHelper;
  import org.htmlunit.javascript.HtmlUnitScriptable;
  import org.htmlunit.javascript.host.event.Event;
  import org.htmlunit.xpath.xml.utils.PrefixResolver;
  import org.w3c.dom.DOMException;
  import org.w3c.dom.Document;
  import org.w3c.dom.NamedNodeMap;
  import org.w3c.dom.Node;
  import org.w3c.dom.UserDataHandler;
  import org.xml.sax.SAXException;
  
  /**
   * Base class for nodes in the HTML DOM tree. This class is modeled after the
   * W3C DOM specification, but does not implement it.
   *
   * @author <a href="mailto:mbowler@GargoyleSoftware.com">Mike Bowler</a>
   * @author <a href="mailto:gudujarlson@sf.net">Mike J. Bresnahan</a>
   * @author David K. Taylor
   * @author <a href="mailto:cse@dynabean.de">Christian Sell</a>
   * @author Chris Erskine
   * @author Mike Williams
   * @author Marc Guillemot
   * @author Denis N. Antonioli
   * @author Daniel Gredler
   * @author Ahmed Ashour
   * @author Rodney Gitzel
   * @author Sudhan Moghe
   * @author <a href="mailto:tom.anderson@univ.oxon.org">Tom Anderson</a>
   * @author Ronald Brill
   * @author Chuck Dumont
   * @author Frank Danek
   */
  public abstract class DomNode implements Cloneable, Serializable, Node {
  
      /** A ready state constant (state 1). */
      public static final String READY_STATE_UNINITIALIZED = "uninitialized";
  
      /** A ready state constant (state 2). */
      public static final String READY_STATE_LOADING = "loading";
  
      /** A ready state constant (state 3). */
      public static final String READY_STATE_LOADED = "loaded";
  
      /** A ready state constant (state 4). */
      public static final String READY_STATE_INTERACTIVE = "interactive";
  
      /** A ready state constant (state 5). */
      public static final String READY_STATE_COMPLETE = "complete";
  
      /** The name of the "element" property. Used when watching property change events. */
      public static final String PROPERTY_ELEMENT = "element";
 
     private static final NamedNodeMap EMPTY_NAMED_NODE_MAP = new ReadOnlyEmptyNamedNodeMapImpl();
 
     /** The owning page of this node. */
     private SgmlPage page_;
 
     /** The parent node. */
     private DomNode parent_;
 
     /**
      * The previous sibling. The first child's <code>previousSibling</code> points
      * to the end of the list
      */
     private DomNode previousSibling_;
 
     /**
      * The next sibling. The last child's <code>nextSibling</code> is {@code null}
      */
     private DomNode nextSibling_;
 
     /** Start of the child list. */
     private DomNode firstChild_;
 
     /**
      * This is the JavaScript object corresponding to this DOM node. It may
      * be null if there isn't a corresponding JavaScript object.
      */
     private HtmlUnitScriptable scriptObject_;
 
     /** The ready state is an value that is available to a large number of elements. */
     private String readyState_;
 
     /**
      * The line number in the source page where the DOM node starts.
      */
     private int startLineNumber_ = -1;
 
     /**
      * The column number in the source page where the DOM node starts.
      */
     private int startColumnNumber_ = -1;
 
     /**
      * The line number in the source page where the DOM node ends.
      */
     private int endLineNumber_ = -1;
 
     /**
      * The column number in the source page where the DOM node ends.
      */
     private int endColumnNumber_ = -1;
 
     private boolean attachedToPage_;
 
     /** The listeners which are to be notified of characterData change. */
     private List<CharacterDataChangeListener> characterDataListeners_;
     private List<DomChangeListener> domListeners_;
 
     private Map<String, Object> userData_;
 
     /**
      * Creates a new instance.
      * @param page the page which contains this node
      */
     protected DomNode(final SgmlPage page) {
         readyState_ = READY_STATE_LOADING;
         page_ = page;
     }
 
     /**
      * Sets the line and column numbers in the source page where the DOM node starts.
      *
      * @param startLineNumber the line number where the DOM node starts
      * @param startColumnNumber the column number where the DOM node starts
      */
     public void setStartLocation(final int startLineNumber, final int startColumnNumber) {
         startLineNumber_ = startLineNumber;
         startColumnNumber_ = startColumnNumber;
     }
 
     /**
      * Sets the line and column numbers in the source page where the DOM node ends.
      *
      * @param endLineNumber the line number where the DOM node ends
      * @param endColumnNumber the column number where the DOM node ends
      */
     public void setEndLocation(final int endLineNumber, final int endColumnNumber) {
         endLineNumber_ = endLineNumber;
         endColumnNumber_ = endColumnNumber;
     }
 
     /**
      * Returns the line number in the source page where the DOM node starts.
      * @return the line number in the source page where the DOM node starts
      */
     public int getStartLineNumber() {
         return startLineNumber_;
     }
 
     /**
      * Returns the column number in the source page where the DOM node starts.
      * @return the column number in the source page where the DOM node starts
      */
     public int getStartColumnNumber() {
         return startColumnNumber_;
     }
 
     /**
      * Returns the line number in the source page where the DOM node ends.
      * @return 0 if no information on the line number is available (for instance for nodes dynamically added),
      *         -1 if the end tag has not yet been parsed (during page loading)
      */
     public int getEndLineNumber() {
         return endLineNumber_;
     }
 
     /**
      * Returns the column number in the source page where the DOM node ends.
      * @return 0 if no information on the line number is available (for instance for nodes dynamically added),
      *         -1 if the end tag has not yet been parsed (during page loading)
      */
     public int getEndColumnNumber() {
         return endColumnNumber_;
     }
 
     /**
      * Returns the page that contains this node.
      * @return the page that contains this node
      */
     public SgmlPage getPage() {
         return page_;
     }
 
     /**
      * Returns the page that contains this node.
      * @return the page that contains this node
      */
     public HtmlPage getHtmlPageOrNull() {
         if (page_ == null || !page_.isHtmlPage()) {
             return null;
         }
         return (HtmlPage) page_;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Document getOwnerDocument() {
         return getPage();
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * Sets the JavaScript object that corresponds to this node. This is not guaranteed to be set even if
      * there is a JavaScript object for this DOM node.
      *
      * @param scriptObject the JavaScript object
      */
     public void setScriptableObject(final HtmlUnitScriptable scriptObject) {
         scriptObject_ = scriptObject;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public DomNode getLastChild() {
         if (firstChild_ != null) {
             // last child is stored as the previous sibling of first child
             return firstChild_.previousSibling_;
         }
         return null;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public DomNode getParentNode() {
         return parent_;
     }
 
     /**
      * Sets the parent node.
      * @param parent the parent node
      */
     protected void setParentNode(final DomNode parent) {
         parent_ = parent;
     }
 
     /**
      * Returns this node's index within its parent's child nodes (zero-based).
      * @return this node's index within its parent's child nodes (zero-based)
      */
     public int getIndex() {
         int index = 0;
         for (DomNode n = previousSibling_; n != null && n.nextSibling_ != null; n = n.previousSibling_) {
             index++;
         }
         return index;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public DomNode getPreviousSibling() {
         if (parent_ == null || this == parent_.firstChild_) {
             // previous sibling of first child points to last child
             return null;
         }
         return previousSibling_;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public DomNode getNextSibling() {
         return nextSibling_;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public DomNode getFirstChild() {
         return firstChild_;
     }
 
     /**
      * Returns {@code true} if this node is an ancestor of the specified node.
      *
      * @param node the node to check
      * @return {@code true} if this node is an ancestor of the specified node
      */
     public boolean isAncestorOf(DomNode node) {
         while (node != null) {
             if (node == this) {
                 return true;
             }
             node = node.getParentNode();
         }
         return false;
     }
 
     /**
      * Returns {@code true} if this node is an ancestor of the specified nodes.
      *
      * @param nodes the nodes to check
      * @return {@code true} if this node is an ancestor of the specified nodes
      */
     public boolean isAncestorOfAny(final DomNode... nodes) {
         for (final DomNode node : nodes) {
             if (isAncestorOf(node)) {
                 return true;
             }
         }
         return false;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getNamespaceURI() {
         return null;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getLocalName() {
         return null;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getPrefix() {
         return null;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean hasChildNodes() {
         return firstChild_ != null;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public DomNodeList<DomNode> getChildNodes() {
         return new SiblingDomNodeList(this);
     }
 
     /**
      * {@inheritDoc}
      * Not yet implemented.
      */
     @Override
     public boolean isSupported(final String namespace, final String featureName) {
         throw new UnsupportedOperationException("DomNode.isSupported is not yet implemented.");
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void normalize() {
         for (DomNode child = getFirstChild(); child != null; child = child.getNextSibling()) {
             if (child instanceof DomText) {
                 final StringBuilder dataBuilder = new StringBuilder();
                 DomNode toRemove = child;
                 DomText firstText = null;
                 //IE removes all child text nodes, but FF preserves the first
                 while (toRemove instanceof DomText && !(toRemove instanceof DomCDataSection)) {
                     final DomNode nextChild = toRemove.getNextSibling();
                     dataBuilder.append(toRemove.getTextContent());
                     if (firstText != null) {
                         toRemove.remove();
                     }
                     if (firstText == null) {
                         firstText = (DomText) toRemove;
                     }
                     toRemove = nextChild;
                 }
                 if (firstText != null) {
                     firstText.setData(dataBuilder.toString());
                 }
             }
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getBaseURI() {
         return getPage().getUrl().toExternalForm();
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public short compareDocumentPosition(final Node other) {
         if (other == this) {
             return 0; // strange, no constant available?
         }
 
         // get ancestors of both
         final List<Node> myAncestors = getAncestors();
         final List<Node> otherAncestors = ((DomNode) other).getAncestors();
 
         if (!myAncestors.get(0).equals(otherAncestors.get(0))) {
             // spec likes to have a consistent order
             //
             // If ... node1’s root is not node2’s root, then return the result of adding
             // DOCUMENT_POSITION_DISCONNECTED, DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC,
             // and either DOCUMENT_POSITION_PRECEDING or DOCUMENT_POSITION_FOLLOWING,
             // with the constraint that this is to be consistent...
             if (this.hashCode() < other.hashCode()) {
                 return DOCUMENT_POSITION_DISCONNECTED
                         | DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC
                         | DOCUMENT_POSITION_PRECEDING;
             }
 
             return DOCUMENT_POSITION_DISCONNECTED
                     | DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC
                     | DOCUMENT_POSITION_FOLLOWING;
         }
 
         final int max = Math.min(myAncestors.size(), otherAncestors.size());
 
         int i = 1;
         while (i < max && myAncestors.get(i) == otherAncestors.get(i)) {
             i++;
         }
 
         if (i != 1 && i == max) {
             if (myAncestors.size() == max) {
                 return DOCUMENT_POSITION_CONTAINED_BY | DOCUMENT_POSITION_FOLLOWING;
             }
             return DOCUMENT_POSITION_CONTAINS | DOCUMENT_POSITION_PRECEDING;
         }
 
         if (max == 1) {
             if (myAncestors.contains(other)) {
                 return DOCUMENT_POSITION_CONTAINS;
             }
             if (otherAncestors.contains(this)) {
                 return DOCUMENT_POSITION_CONTAINED_BY | DOCUMENT_POSITION_FOLLOWING;
             }
             return DOCUMENT_POSITION_DISCONNECTED | DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC;
         }
 
         // neither contains nor contained by
         final Node myAncestor = myAncestors.get(i);
         final Node otherAncestor = otherAncestors.get(i);
         Node node = myAncestor;
         while (node != otherAncestor && node != null) {
             node = node.getPreviousSibling();
         }
         if (node == null) {
             return DOCUMENT_POSITION_FOLLOWING;
         }
         return DOCUMENT_POSITION_PRECEDING;
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * Gets the ancestors of the node.
      * @return a list of the ancestors with the root at the first position
      */
     public List<Node> getAncestors() {
         final List<Node> list = new ArrayList<>();
         list.add(this);
 
         Node node = getParentNode();
         while (node != null) {
             list.add(0, node);
             node = node.getParentNode();
         }
         return list;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getTextContent() {
         switch (getNodeType()) {
             case ELEMENT_NODE:
             case ATTRIBUTE_NODE:
             case ENTITY_NODE:
             case ENTITY_REFERENCE_NODE:
             case DOCUMENT_FRAGMENT_NODE:
                 final StringBuilder builder = new StringBuilder();
                 for (final DomNode child : getChildren()) {
                     final short childType = child.getNodeType();
                     if (childType != COMMENT_NODE && childType != PROCESSING_INSTRUCTION_NODE) {
                         builder.append(child.getTextContent());
                     }
                 }
                 return builder.toString();
 
             case TEXT_NODE:
             case CDATA_SECTION_NODE:
             case COMMENT_NODE:
             case PROCESSING_INSTRUCTION_NODE:
                 return getNodeValue();
 
             default:
                 return null;
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void setTextContent(final String textContent) {
         removeAllChildren();
         if (textContent != null && !textContent.isEmpty()) {
             appendChild(new DomText(getPage(), textContent));
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isSameNode(final Node other) {
         return other == this;
     }
 
     /**
      * {@inheritDoc}
      * Not yet implemented.
      */
     @Override
     public String lookupPrefix(final String namespaceURI) {
         throw new UnsupportedOperationException("DomNode.lookupPrefix is not yet implemented.");
     }
 
     /**
      * {@inheritDoc}
      * Not yet implemented.
      */
     @Override
     public boolean isDefaultNamespace(final String namespaceURI) {
         throw new UnsupportedOperationException("DomNode.isDefaultNamespace is not yet implemented.");
     }
 
     /**
      * {@inheritDoc}
      * Not yet implemented.
      */
     @Override
     public String lookupNamespaceURI(final String prefix) {
         throw new UnsupportedOperationException("DomNode.lookupNamespaceURI is not yet implemented.");
     }
 
     /**
      * {@inheritDoc}
      * Not yet implemented.
      */
     @Override
     public boolean isEqualNode(final Node arg) {
         throw new UnsupportedOperationException("DomNode.isEqualNode is not yet implemented.");
     }
 
     /**
      * {@inheritDoc}
      * Not yet implemented.
      */
     @Override
     public Object getFeature(final String feature, final String version) {
         throw new UnsupportedOperationException("DomNode.getFeature is not yet implemented.");
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Object getUserData(final String key) {
         Object value = null;
         if (userData_ != null) {
             value = userData_.get(key);
         }
         return value;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Object setUserData(final String key, final Object data, final UserDataHandler handler) {
         if (userData_ == null) {
             userData_ = new HashMap<>();
         }
         return userData_.put(key, data);
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean hasAttributes() {
         return false;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public NamedNodeMap getAttributes() {
         return EMPTY_NAMED_NODE_MAP;
     }
 
     /**
      * <p>Returns {@code true} if this node is displayed and can be visible to the user
      * (ignoring screen size, scrolling limitations, color, font-size, or overlapping nodes).</p>
      *
      * <p><b>NOTE:</b> If CSS is
      * {@link org.htmlunit.WebClientOptions#setCssEnabled(boolean) disabled}, this method
      * does <b>not</b> take this element's style into consideration!</p>
      *
      * @see <a href="http://www.w3.org/TR/CSS2/visufx.html#visibility">CSS2 Visibility</a>
      * @see <a href="http://www.w3.org/TR/CSS2/visuren.html#propdef-display">CSS2 Display</a>
      * @see <a href="http://msdn.microsoft.com/en-us/library/ms531180.aspx">MSDN Documentation</a>
      * @return {@code true} if the node is visible to the user, {@code false} otherwise
      * @see #mayBeDisplayed()
      */
     public boolean isDisplayed() {
         if (!mayBeDisplayed()) {
             return false;
         }
 
         final Page page = getPage();
         final WebWindow window = page.getEnclosingWindow();
         final WebClient webClient = window.getWebClient();
         if (webClient.getOptions().isCssEnabled()) {
             // display: iterate top to bottom, because if a parent is display:none,
             // there's nothing that a child can do to override it
             final List<Node> ancestors = getAncestors();
             final ArrayList<ComputedCssStyleDeclaration> styles = new ArrayList<>(ancestors.size());
 
             for (final Node node : ancestors) {
                 if (node instanceof HtmlElement) {
                     final HtmlElement elem = (HtmlElement) node;
                     if (elem.isHidden()) {
                         return false;
                     }
 
                     if (elem instanceof HtmlDialog) {
                         if (!((HtmlDialog) elem).isOpen()) {
                             return false;
                         }
                     }
                     else {
                         final ComputedCssStyleDeclaration style = window.getComputedStyle(elem, null);
                         if (DisplayStyle.NONE.value().equals(style.getDisplay())) {
                             return false;
                         }
                         styles.add(style);
                     }
                 }
             }
 
             // visibility: iterate bottom to top, because children can override
             // the visibility used by parent nodes
             for (int i = styles.size() - 1; i >= 0; i--) {
                 final ComputedCssStyleDeclaration style = styles.get(i);
                 final String visibility = style.getStyleAttribute(StyleAttributes.Definition.VISIBILITY, true);
                 if (visibility.length() > 5) {
                     if ("visible".equals(visibility)) {
                         return true;
                     }
                     if ("hidden".equals(visibility) || "collapse".equals(visibility)) {
                         return false;
                     }
                 }
             }
         }
         return true;
     }
 
     /**
      * Returns {@code true} if nodes of this type can ever be displayed, {@code false} otherwise. Examples of nodes
      * that can never be displayed are <code>&lt;head&gt;</code>,
      * <code>&lt;meta&gt;</code>, <code>&lt;script&gt;</code>, etc.
      * @return {@code true} if nodes of this type can ever be displayed, {@code false} otherwise
      * @see #isDisplayed()
      */
     public boolean mayBeDisplayed() {
         return true;
     }
 
     /**
      * Returns a normalized textual representation of this element that represents
      * what would be visible to the user if this page was shown in a web browser.
      * Whitespace is normalized like in the browser and block tags are separated by '\n'.
      *
      * @return a normalized textual representation of this element
      */
     public String asNormalizedText() {
         final HtmlSerializerNormalizedText ser = new HtmlSerializerNormalizedText();
         return ser.asText(this);
     }
 
     /**
      * Returns a textual representation of this element in the same way as
      * the selenium/WebDriver WebElement#getText() property does.<br>
      * see <a href="https://w3c.github.io/webdriver/#get-element-text">get-element-text</a> and
      * <a href="https://w3c.github.io/webdriver/#dfn-bot-dom-getvisibletext">dfn-bot-dom-getvisibletext</a>
      * Note: this is different from {@link #asNormalizedText()}
      *
      * @return a textual representation of this element that represents what would
      *         be visible to the user if this page was shown in a web browser
      */
     public String getVisibleText() {
         final HtmlSerializerVisibleText ser = new HtmlSerializerVisibleText();
         return ser.asText(this);
     }
 
     /**
      * Returns a string representation as XML document from this element and all it's children (recursively).<br>
      * The charset used in the xml header is the current page encoding; but the result is still a string.
      * You have to make sure to use the correct (in fact the same) encoding if you write this to a file.<br>
      * This serializes the current state of the DomTree - this implies that the content of noscript tags
      * usually serialized as string because the content is converted during parsing (if js was enabled at that time).
      * @return the XML string
      */
     public String asXml() {
         Charset charsetName = null;
         final HtmlPage htmlPage = getHtmlPageOrNull();
         if (htmlPage != null) {
             charsetName = htmlPage.getCharset();
         }
 
         final StringWriter stringWriter = new StringWriter();
         try (PrintWriter printWriter = new PrintWriter(stringWriter)) {
             boolean tag = false;
             if (charsetName != null && this instanceof HtmlHtml) {
                 printWriter.print("<?xml version=\"1.0\" encoding=\"");
                 printWriter.print(charsetName);
                 printWriter.print("\"?>");
                 tag = true;
             }
             printXml("", tag, printWriter);
             return stringWriter.toString();
         }
     }
 
     /**
      * Recursively writes the XML data for the node tree starting at <code>node</code>.
      *
      * @param indent white space to indent child nodes
      * @param tagBefore true if the last thing printed was a tag
      * @param printWriter writer where child nodes are written
      * @return true if the last thing printed was a tag
      */
     protected boolean printXml(final String indent, final boolean tagBefore, final PrintWriter printWriter) {
         if (tagBefore) {
             printWriter.print("\r\n");
             printWriter.print(indent);
         }
         printWriter.print(this);
         return printChildrenAsXml(indent, false, printWriter);
     }
 
     /**
      * Recursively writes the XML data for the node tree starting at <code>node</code>.
      *
      * @param indent white space to indent child nodes
      * @param tagBefore true if the last thing printed was a tag
      * @param printWriter writer where child nodes are written
      * @return true if the last thing printed was a tag
      */
     protected boolean printChildrenAsXml(final String indent, final boolean tagBefore, final PrintWriter printWriter) {
         DomNode child = getFirstChild();
         boolean tag = tagBefore;
         while (child != null) {
             tag = child.printXml(indent + "  ", tag, printWriter);
             child = child.getNextSibling();
         }
         return tag;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getNodeValue() {
         return null;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public DomNode cloneNode(final boolean deep) {
         final DomNode newnode;
         try {
             newnode = (DomNode) clone();
         }
         catch (final CloneNotSupportedException e) {
             throw new IllegalStateException("Clone not supported for node [" + this + "]", e);
         }
 
         newnode.parent_ = null;
         newnode.nextSibling_ = null;
         newnode.previousSibling_ = null;
         newnode.scriptObject_ = null;
         newnode.firstChild_ = null;
         newnode.attachedToPage_ = false;
 
         // if deep, clone the children too.
         if (deep) {
             for (DomNode child = firstChild_; child != null; child = child.nextSibling_) {
                 newnode.appendChild(child.cloneNode(true));
             }
         }
 
         return newnode;
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * <p>Returns the JavaScript object that corresponds to this node, lazily initializing a new one if necessary.</p>
      *
      * <p>The logic of when and where the JavaScript object is created needs a clean up: functions using
      * a DOM node's JavaScript object should not have to check if they should create it first.</p>
      *
      * @param <T> the object type
      * @return the JavaScript object that corresponds to this node
      */
     @SuppressWarnings("unchecked")
     public <T extends HtmlUnitScriptable> T getScriptableObject() {
         if (scriptObject_ == null) {
             final SgmlPage page = getPage();
             if (this == page) {
                 final StringBuilder msg = new StringBuilder("No script object associated with the Page.");
                 // because this is a strange case we like to provide as much info as possible
                 msg.append(" class: '")
                     .append(page.getClass().getName())
                     .append('\'');
                 try {
                     msg.append(" url: '")
                         .append(page.getUrl()).append("' content: ")
                         .append(page.getWebResponse().getContentAsString());
                 }
                 catch (final Exception e) {
                     // ok bad luck with detail
                     msg.append(" no details: '").append(e).append('\'');
                 }
                 throw new IllegalStateException(msg.toString());
             }
             scriptObject_ = page.getScriptableObject().makeScriptableFor(this);
         }
         return (T) scriptObject_;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public DomNode appendChild(final Node node) {
         if (node == this) {
             throw new DOMException(DOMException.HIERARCHY_REQUEST_ERR, "Can not add not to itself " + this);
         }
         final DomNode domNode = (DomNode) node;
         if (domNode.isAncestorOf(this)) {
             throw new DOMException(DOMException.HIERARCHY_REQUEST_ERR, "Can not add (grand)parent to itself " + this);
         }
 
         if (domNode instanceof DomDocumentFragment) {
             final DomDocumentFragment fragment = (DomDocumentFragment) domNode;
             for (final DomNode child : fragment.getChildren()) {
                 appendChild(child);
             }
         }
         else {
             // clean up the new node, in case it is being moved
             if (domNode.getParentNode() != null) {
                 domNode.detach();
             }
 
             basicAppend(domNode);
 
             fireAddition(domNode);
         }
 
         return domNode;
     }
 
     /**
      * Appends the specified node to the end of this node's children, assuming the specified
      * node is clean (doesn't have preexisting relationships to other nodes).
      *
      * @param node the node to append to this node's children
      */
     private void basicAppend(final DomNode node) {
         // try to make the node setup as complete as possible
         // before the node is reachable
         node.setPage(getPage());
         node.parent_ = this;
 
         if (firstChild_ == null) {
             firstChild_ = node;
         }
         else {
             final DomNode last = getLastChild();
             node.previousSibling_ = last;
             node.nextSibling_ = null; // safety first
 
             last.nextSibling_ = node;
         }
         firstChild_.previousSibling_ = node;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Node insertBefore(final Node newChild, final Node refChild) {
         if (newChild instanceof DomDocumentFragment) {
             final DomDocumentFragment fragment = (DomDocumentFragment) newChild;
             for (final DomNode child : fragment.getChildren()) {
                 insertBefore(child, refChild);
             }
             return newChild;
         }
 
         if (refChild == null) {
             appendChild(newChild);
             return newChild;
         }
 
         if (refChild.getParentNode() != this) {
             throw new DOMException(DOMException.NOT_FOUND_ERR, "Reference node is not a child of this node.");
         }
 
         ((DomNode) refChild).insertBefore((DomNode) newChild);
         return newChild;
     }
 
     /**
      * Inserts the specified node as a new child node before this node into the child relationship this node is a
      * part of. If the specified node is this node, this method is a no-op.
      *
      * @param newNode the new node to insert
      */
     public void insertBefore(final DomNode newNode) {
         if (previousSibling_ == null) {
             throw new IllegalStateException("Previous sibling for " + this + " is null.");
         }
 
         if (newNode == this) {
             return;
         }
 
         // clean up the new node, in case it is being moved
         if (newNode.getParentNode() != null) {
             newNode.detach();
         }
 
         basicInsertBefore(newNode);
 
         fireAddition(newNode);
     }
 
     /**
      * Inserts the specified node into this node's parent's children right before this node, assuming the specified
      * node is clean (doesn't have preexisting relationships to other nodes).
      *
      * @param node the node to insert before this node
      */
     private void basicInsertBefore(final DomNode node) {
         // try to make the node setup as complete as possible
         // before the node is reachable
         node.setPage(page_);
         node.parent_ = parent_;
         node.previousSibling_ = previousSibling_;
         node.nextSibling_ = this;
 
         if (parent_.firstChild_ == this) {
             parent_.firstChild_ = node;
         }
         else {
             previousSibling_.nextSibling_ = node;
         }
         previousSibling_ = node;
     }
 
     private void fireAddition(final DomNode domNode) {
         final boolean wasAlreadyAttached = domNode.isAttachedToPage();
         domNode.attachedToPage_ = isAttachedToPage();
 
         final SgmlPage page = getPage();
         if (domNode.attachedToPage_) {
             // trigger events
             if (null != page && page.isHtmlPage()) {
                 ((HtmlPage) page).notifyNodeAdded(domNode);
             }
 
             // a node that is already "complete" (ie not being parsed) and not yet attached
             if (!domNode.isBodyParsed() && !wasAlreadyAttached) {
                 if (domNode.getFirstChild() != null) {
                     for (final Iterator<DomNode> iterator =
                             domNode.new DescendantDomNodesIterator(); iterator.hasNext();) {
                         final DomNode child = iterator.next();
                         child.attachedToPage_ = true;
                         child.onAllChildrenAddedToPage(true);
                     }
                 }
                 domNode.onAllChildrenAddedToPage(true);
             }
         }
 
         if (this instanceof DomDocumentFragment) {
             onAddedToDocumentFragment();
         }
 
         if (page == null || page.isDomChangeListenerInUse()) {
             fireNodeAdded(this, domNode);
         }
     }
 
     /**
      * Indicates if the current node is being parsed. This means that the opening tag has already been
      * parsed but not the body and end tag.
      */
     private boolean isBodyParsed() {
         return getStartLineNumber() != -1 && getEndLineNumber() == -1;
     }
 
     /**
      * Recursively sets the new page on the node and its children
      * @param newPage the new owning page
      */
     private void setPage(final SgmlPage newPage) {
         if (page_ == newPage) {
             return; // nothing to do
         }
 
         page_ = newPage;
         for (final DomNode node : getChildren()) {
             node.setPage(newPage);
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Node removeChild(final Node child) {
         if (child.getParentNode() != this) {
             throw new DOMException(DOMException.NOT_FOUND_ERR, "Node is not a child of this node.");
         }
         ((DomNode) child).remove();
         return child;
     }
 
     /**
      * Removes all of this node's children.
      */
     public void removeAllChildren() {
         while (getFirstChild() != null) {
             getFirstChild().remove();
         }
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * Parses the specified HTML source code, appending the resulting content at the specified target location.
      * @param source the HTML code extract to parse
      * @throws IOException in case of error
      * @throws SAXException in case of error
      */
     public void parseHtmlSnippet(final String source) throws SAXException, IOException {
         final WebClient webClient = getPage().getWebClient();
         webClient.getPageCreator().getHtmlParser().parseFragment(webClient, this, this, source, false);
     }
 
     /**
      * Removes this node from all relationships with other nodes.
      */
     public void remove() {
         // same as detach for the moment
         detach();
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * Detach this node from all relationships with other nodes.
      * This is the first step of a move.
      */
     protected void detach() {
         final DomNode exParent = parent_;
 
         basicRemove();
 
         fireRemoval(exParent);
     }
 
     /**
      * Cuts off all relationships this node has with siblings and parents.
      */
     protected void basicRemove() {
         if (parent_ != null && parent_.firstChild_ == this) {
             parent_.firstChild_ = nextSibling_;
         }
         else if (previousSibling_ != null && previousSibling_.nextSibling_ == this) {
             previousSibling_.nextSibling_ = nextSibling_;
         }
         if (nextSibling_ != null && nextSibling_.previousSibling_ == this) {
             nextSibling_.previousSibling_ = previousSibling_;
         }
         if (parent_ != null && this == parent_.getLastChild()) {
             parent_.firstChild_.previousSibling_ = previousSibling_;
         }
 
         nextSibling_ = null;
         previousSibling_ = null;
         parent_ = null;
         attachedToPage_ = false;
         for (final DomNode descendant : getDescendants()) {
             descendant.attachedToPage_ = false;
         }
     }
 
     private void fireRemoval(final DomNode exParent) {
         final SgmlPage page = getPage();
         if (page instanceof HtmlPage) {
             // some actions executed on removal need an intact parent relationship (e.g. for the
             // DocumentPositionComparator) so we have to restore it temporarily
             parent_ = exParent;
             ((HtmlPage) page).notifyNodeRemoved(this);
             parent_ = null;
         }
 
         if (exParent != null && (page == null || page.isDomChangeListenerInUse())) {
             fireNodeDeleted(exParent, this);
             // ask ex-parent to fire event (because we don't have parent now)
             exParent.fireNodeDeleted(exParent, this);
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Node replaceChild(final Node newChild, final Node oldChild) {
         if (oldChild.getParentNode() != this) {
             throw new DOMException(DOMException.NOT_FOUND_ERR, "Node is not a child of this node.");
         }
         ((DomNode) oldChild).replace((DomNode) newChild);
         return oldChild;
     }
 
     /**
      * Replaces this node with another node. If the specified node is this node, this
      * method is a no-op.
      * @param newNode the node to replace this one
      */
     public void replace(final DomNode newNode) {
         if (newNode != this) {
             final DomNode exParent = parent_;
             final DomNode exNextSibling = nextSibling_;
 
             remove();
 
             exParent.insertBefore(newNode, exNextSibling);
         }
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * Quietly removes this node and moves its children to the specified destination. "Quietly" means
      * that no node events are fired. This method is not appropriate for most use cases. It should
      * only be used in specific cases for HTML parsing hackery.
      *
      * @param destination the node to which this node's children should be moved before this node is removed
      */
     public void quietlyRemoveAndMoveChildrenTo(final DomNode destination) {
         if (destination.getPage() != getPage()) {
             throw new RuntimeException("Cannot perform quiet move on nodes from different pages.");
         }
         for (final DomNode child : getChildren()) {
             if (child != destination) {
                 child.basicRemove();
                 destination.basicAppend(child);
             }
         }
         basicRemove();
     }
 
     /**
      * Check for insertion errors for a new child node. This is overridden by derived
      * classes to enforce which types of children are allowed.
      *
      * @param newChild the new child node that is being inserted below this node
      * @throws DOMException HIERARCHY_REQUEST_ERR: Raised if this node is of a type that does
      *         not allow children of the type of the newChild node, or if the node to insert is one of
      *         this node's ancestors or this node itself, or if this node is of type Document and the
      *         DOM application attempts to insert a second DocumentType or Element node.
      *         WRONG_DOCUMENT_ERR: Raised if newChild was created from a different document than the
      *         one that created this node.
      */
     protected void checkChildHierarchy(final Node newChild) throws DOMException {
         Node parentNode = this;
         while (parentNode != null) {
             if (parentNode == newChild) {
                 throw new DOMException(DOMException.HIERARCHY_REQUEST_ERR, "Child node is already a parent.");
             }
             parentNode = parentNode.getParentNode();
         }
         final Document thisDocument = getOwnerDocument();
         final Document childDocument = newChild.getOwnerDocument();
         if (childDocument != thisDocument && childDocument != null) {
             throw new DOMException(DOMException.WRONG_DOCUMENT_ERR, "Child node " + newChild.getNodeName()
                 + " is not in the same Document as this " + getNodeName() + ".");
         }
     }
 
     /**
      * Lifecycle method invoked whenever a node is added to a page. Intended to
      * be overridden by nodes which need to perform custom logic when they are
      * added to a page. This method is recursive, so if you override it, please
      * be sure to call <code>super.onAddedToPage()</code>.
      */
     protected void onAddedToPage() {
         if (firstChild_ != null) {
             for (final DomNode child : getChildren()) {
                 child.onAddedToPage();
             }
         }
     }
 
     /**
      * Lifecycle method invoked after a node and all its children have been added to a page, during
      * parsing of the HTML. Intended to be overridden by nodes which need to perform custom logic
      * after they and all their child nodes have been processed by the HTML parser. This method is
      * not recursive, and the default implementation is empty, so there is no need to call
      * <code>super.onAllChildrenAddedToPage()</code> if you implement this method.
      * @param postponed whether to use {@link org.htmlunit.javascript.PostponedAction} or no
      */
     public void onAllChildrenAddedToPage(final boolean postponed) {
         // Empty by default.
     }
 
     /**
      * Lifecycle method invoked whenever a node is added to a document fragment. Intended to
      * be overridden by nodes which need to perform custom logic when they are
      * added to a fragment. This method is recursive, so if you override it, please
      * be sure to call <code>super.onAddedToDocumentFragment()</code>.
      */
     protected void onAddedToDocumentFragment() {
         if (firstChild_ != null) {
             for (final DomNode child : getChildren()) {
                 child.onAddedToDocumentFragment();
             }
         }
     }
 
     /**
      * @return an {@link Iterable} over the children of this node
      */
     public final Iterable<DomNode> getChildren() {
         return () -> new ChildIterator(firstChild_);
     }
 
     /**
      * An iterator over all children of this node.
      */
     protected static class ChildIterator implements Iterator<DomNode> {
 
         private DomNode nextNode_;
         private DomNode currentNode_;
 
         public ChildIterator(final DomNode nextNode) {
             nextNode_ = nextNode;
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean hasNext() {
             return nextNode_ != null;
         }
 
         /** {@inheritDoc} */
         @Override
         public DomNode next() {
             if (nextNode_ != null) {
                 currentNode_ = nextNode_;
                 nextNode_ = nextNode_.nextSibling_;
                 return currentNode_;
             }
             throw new NoSuchElementException();
         }
 
         /** {@inheritDoc} */
         @Override
         public void remove() {
             if (currentNode_ == null) {
                 throw new IllegalStateException();
             }
             currentNode_.remove();
         }
     }
 
     /**
      * Returns an {@link Iterable} that will recursively iterate over all of this node's descendants,
      * including {@link DomText} elements, {@link DomComment} elements, etc. If you want to iterate
      * only over {@link HtmlElement} descendants, please use {@link #getHtmlElementDescendants()}.
      * @return an {@link Iterable} that will recursively iterate over all of this node's descendants
      */
     public final Iterable<DomNode> getDescendants() {
         return () -> new DescendantDomNodesIterator();
     }
 
     /**
      * Returns an {@link Iterable} that will recursively iterate over all of this node's {@link HtmlElement}
      * descendants. If you want to iterate over all descendants (including {@link DomText} elements,
      * {@link DomComment} elements, etc.), please use {@link #getDescendants()}.
      * @return an {@link Iterable} that will recursively iterate over all of this node's {@link HtmlElement}
      *         descendants
      * @see #getDomElementDescendants()
      */
     public final Iterable<HtmlElement> getHtmlElementDescendants() {
         return () -> new DescendantHtmlElementsIterator();
     }
 
     /**
      * Returns an {@link Iterable} that will recursively iterate over all of this node's {@link DomElement}
      * descendants. If you want to iterate over all descendants (including {@link DomText} elements,
      * {@link DomComment} elements, etc.), please use {@link #getDescendants()}.
      * @return an {@link Iterable} that will recursively iterate over all of this node's {@link DomElement}
      *         descendants
      * @see #getHtmlElementDescendants()
      */
     public final Iterable<DomElement> getDomElementDescendants() {
         return () -> new DescendantDomElementsIterator();
     }
 
     /**
      * Iterates over all descendants of a specific type, in document order.
      * @param <T> the type of nodes over which to iterate
      *
      * @deprecated as of version 4.7.0; use {@link DescendantDomNodesIterator},
      *     {@link DescendantDomElementsIterator}, or {@link DescendantHtmlElementsIterator} instead.
      */
     @Deprecated
     protected class DescendantElementsIterator<T extends DomNode> implements Iterator<T> {
 
         private DomNode currentNode_;
         private DomNode nextNode_;
         private final Class<T> type_;
 
         /**
          * Creates a new instance which iterates over the specified node type.
          * @param type the type of nodes over which to iterate
          */
         public DescendantElementsIterator(final Class<T> type) {
             type_ = type;
             nextNode_ = getFirstChildElement(DomNode.this);
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean hasNext() {
             return nextNode_ != null;
         }
 
         /** {@inheritDoc} */
         @Override
         public T next() {
             return nextNode();
         }
 
         /** {@inheritDoc} */
         @Override
         public void remove() {
             if (currentNode_ == null) {
                 throw new IllegalStateException("Unable to remove current node, because there is no current node.");
             }
             final DomNode current = currentNode_;
             while (nextNode_ != null && current.isAncestorOf(nextNode_)) {
                 next();
             }
             current.remove();
         }
 
         /**
          * @return the next node, if there is one
          */
         @SuppressWarnings("unchecked")
         public T nextNode() {
             currentNode_ = nextNode_;
             setNextElement();
             return (T) currentNode_;
         }
 
         private void setNextElement() {
             DomNode next = getFirstChildElement(nextNode_);
             if (next == null) {
                 next = getNextDomSibling(nextNode_);
             }
             if (next == null) {
                 next = getNextElementUpwards(nextNode_);
             }
             nextNode_ = next;
         }
 
         private DomNode getNextElementUpwards(final DomNode startingNode) {
             if (startingNode == DomNode.this) {
                 return null;
             }
 
             DomNode parent = startingNode.getParentNode();
             while (parent != null && parent != DomNode.this) {
                 DomNode next = parent.getNextSibling();
                 while (next != null && !isAccepted(next)) {
                     next = next.getNextSibling();
                 }
                 if (next != null) {
                     return next;
                 }
                 parent = parent.getParentNode();
             }
             return null;
         }
 
         private DomNode getFirstChildElement(final DomNode parent) {
             DomNode node = parent.getFirstChild();
             while (node != null && !isAccepted(node)) {
                 node = node.getNextSibling();
             }
             return node;
         }
 
         /**
          * Indicates if the node is accepted. If not it won't be explored at all.
          * @param node the node to test
          * @return {@code true} if accepted
          */
         protected boolean isAccepted(final DomNode node) {
             return type_.isAssignableFrom(node.getClass());
         }
 
         private DomNode getNextDomSibling(final DomNode element) {
             DomNode node = element.getNextSibling();
             while (node != null && !isAccepted(node)) {
                 node = node.getNextSibling();
             }
             return node;
         }
     }
 
     /**
      * Iterates over all descendants DomNodes, in document order.
      */
     protected final class DescendantDomNodesIterator implements Iterator<DomNode> {
         private DomNode currentNode_;
         private DomNode nextNode_;
 
         /**
          * Creates a new instance which iterates over the specified node type.
          */
         public DescendantDomNodesIterator() {
             nextNode_ = getFirstChildElement(DomNode.this);
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean hasNext() {
             return nextNode_ != null;
         }
 
         /** {@inheritDoc} */
         @Override
         public DomNode next() {
             return nextNode();
         }
 
         /** {@inheritDoc} */
         @Override
         public void remove() {
             if (currentNode_ == null) {
                 throw new IllegalStateException("Unable to remove current node, because there is no current node.");
             }
             final DomNode current = currentNode_;
             while (nextNode_ != null && current.isAncestorOf(nextNode_)) {
                 next();
             }
             current.remove();
         }
 
         /**
          * @return the next node, if there is one
          */
         @SuppressWarnings("unchecked")
         public DomNode nextNode() {
             currentNode_ = nextNode_;
 
             DomNode next = getFirstChildElement(nextNode_);
             if (next == null) {
                 next = getNextDomSibling(nextNode_);
             }
             if (next == null) {
                 next = getNextElementUpwards(nextNode_);
             }
             nextNode_ = next;
 
             return currentNode_;
         }
 
         private DomNode getNextElementUpwards(final DomNode startingNode) {
             if (startingNode == DomNode.this) {
                 return null;
             }
 
             DomNode parent = startingNode.getParentNode();
             while (parent != null && parent != DomNode.this) {
                 DomNode next = parent.getNextSibling();
                 while (next != null && !isAccepted(next)) {
                     next = next.getNextSibling();
                 }
                 if (next != null) {
                     return next;
                 }
                 parent = parent.getParentNode();
             }
             return null;
         }
 
         private DomNode getFirstChildElement(final DomNode parent) {
             DomNode node = parent.getFirstChild();
             while (node != null && !isAccepted(node)) {
                 node = node.getNextSibling();
             }
             return node;
         }
 
         /**
          * Indicates if the node is accepted. If not it won't be explored at all.
          * @param node the node to test
          * @return {@code true} if accepted
          */
         private boolean isAccepted(final DomNode node) {
             return DomNode.class.isAssignableFrom(node.getClass());
         }
 
         private DomNode getNextDomSibling(final DomNode element) {
             DomNode node = element.getNextSibling();
             while (node != null && !isAccepted(node)) {
                 node = node.getNextSibling();
             }
             return node;
         }
     }
 
     /**
      * Iterates over all descendants DomTypes, in document order.
      */
     protected final class DescendantDomElementsIterator implements Iterator<DomElement> {
         private DomNode currentNode_;
         private DomNode nextNode_;
 
         /**
          * Creates a new instance which iterates over the specified node type.
          */
         public DescendantDomElementsIterator() {
             nextNode_ = getFirstChildElement(DomNode.this);
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean hasNext() {
             return nextNode_ != null;
         }
 
         /** {@inheritDoc} */
         @Override
         public DomElement next() {
             return nextNode();
         }
 
         /** {@inheritDoc} */
         @Override
         public void remove() {
             if (currentNode_ == null) {
                 throw new IllegalStateException("Unable to remove current node, because there is no current node.");
             }
             final DomNode current = currentNode_;
             while (nextNode_ != null && current.isAncestorOf(nextNode_)) {
                 next();
             }
             current.remove();
         }
 
         /**
          * @return the next node, if there is one
          */
         @SuppressWarnings("unchecked")
         public DomElement nextNode() {
             currentNode_ = nextNode_;
 
             DomNode next = getFirstChildElement(nextNode_);
             if (next == null) {
                 next = getNextDomSibling(nextNode_);
             }
             if (next == null) {
                 next = getNextElementUpwards(nextNode_);
             }
             nextNode_ = next;
 
             return (DomElement) currentNode_;
         }
 
         private DomNode getNextElementUpwards(final DomNode startingNode) {
             if (startingNode == DomNode.this) {
                 return null;
             }
 
             DomNode parent = startingNode.getParentNode();
             while (parent != null && parent != DomNode.this) {
                 DomNode next = parent.getNextSibling();
                 while (next != null && !isAccepted(next)) {
                     next = next.getNextSibling();
                 }
                 if (next != null) {
                     return next;
                 }
                 parent = parent.getParentNode();
             }
             return null;
         }
 
         private DomNode getFirstChildElement(final DomNode parent) {
             DomNode node = parent.getFirstChild();
             while (node != null && !isAccepted(node)) {
                 node = node.getNextSibling();
             }
             return node;
         }
 
         /**
          * Indicates if the node is accepted. If not it won't be explored at all.
          * @param node the node to test
          * @return {@code true} if accepted
          */
         private boolean isAccepted(final DomNode node) {
             return DomElement.class.isAssignableFrom(node.getClass());
         }
 
         private DomNode getNextDomSibling(final DomNode element) {
             DomNode node = element.getNextSibling();
             while (node != null && !isAccepted(node)) {
                 node = node.getNextSibling();
             }
             return node;
         }
     }
 
     /**
      * Iterates over all descendants HtmlElements, in document order.
      */
     protected final class DescendantHtmlElementsIterator implements Iterator<HtmlElement> {
         private DomNode currentNode_;
         private DomNode nextNode_;
 
         /**
          * Creates a new instance which iterates over the specified node type.
          */
         public DescendantHtmlElementsIterator() {
             nextNode_ = getFirstChildElement(DomNode.this);
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean hasNext() {
             return nextNode_ != null;
         }
 
         /** {@inheritDoc} */
         @Override
         public HtmlElement next() {
             return nextNode();
         }
 
         /** {@inheritDoc} */
         @Override
         public void remove() {
             if (currentNode_ == null) {
                 throw new IllegalStateException("Unable to remove current node, because there is no current node.");
             }
             final DomNode current = currentNode_;
             while (nextNode_ != null && current.isAncestorOf(nextNode_)) {
                 next();
             }
             current.remove();
         }
 
         /**
          * @return the next node, if there is one
          */
         @SuppressWarnings("unchecked")
         public HtmlElement nextNode() {
             currentNode_ = nextNode_;
 
             DomNode next = getFirstChildElement(nextNode_);
             if (next == null) {
                 next = getNextDomSibling(nextNode_);
             }
             if (next == null) {
                 next = getNextElementUpwards(nextNode_);
             }
             nextNode_ = next;
 
             return (HtmlElement) currentNode_;
         }
 
         private DomNode getNextElementUpwards(final DomNode startingNode) {
             if (startingNode == DomNode.this) {
                 return null;
             }
 
             DomNode parent = startingNode.getParentNode();
             while (parent != null && parent != DomNode.this) {
                 DomNode next = parent.getNextSibling();
                 while (next != null && !isAccepted(next)) {
                     next = next.getNextSibling();
                 }
                 if (next != null) {
                     return next;
                 }
                 parent = parent.getParentNode();
             }
             return null;
         }
 
         private DomNode getFirstChildElement(final DomNode parent) {
             DomNode node = parent.getFirstChild();
             while (node != null && !isAccepted(node)) {
                 node = node.getNextSibling();
             }
             return node;
         }
 
         /**
          * Indicates if the node is accepted. If not it won't be explored at all.
          * @param node the node to test
          * @return {@code true} if accepted
          */
         private boolean isAccepted(final DomNode node) {
             return HtmlElement.class.isAssignableFrom(node.getClass());
         }
 
         private DomNode getNextDomSibling(final DomNode element) {
             DomNode node = element.getNextSibling();
             while (node != null && !isAccepted(node)) {
                 node = node.getNextSibling();
             }
             return node;
         }
     }
 
     /**
      * Returns this node's ready state (IE only).
      * @return this node's ready state
      */
     public String getReadyState() {
         return readyState_;
     }
 
     /**
      * Sets this node's ready state (IE only).
      * @param state this node's ready state
      */
     public void setReadyState(final String state) {
         readyState_ = state;
     }
 
     /**
      * Evaluates the specified XPath expression from this node, returning the matching elements.
      * <br>
      * Note: This implies that the ',' point to this node but the general axis like '//' are still
      * looking at the whole document. E.g. if you like to get all child h1 nodes from the current one
      * you have to use './/h1' instead of '//h1' because the latter matches all h1 nodes of the#
      * whole document.
      *
      * @param <T> the expected type
      * @param xpathExpr the XPath expression to evaluate
      * @return the elements which match the specified XPath expression
      * @see #getFirstByXPath(String)
      * @see #getCanonicalXPath()
      */
     public <T> List<T> getByXPath(final String xpathExpr) {
         return XPathHelper.getByXPath(this, xpathExpr, null);
     }
 
     /**
      * Evaluates the specified XPath expression from this node, returning the matching elements.
      *
      * @param xpathExpr the XPath expression to evaluate
      * @param resolver the prefix resolver to use for resolving namespace prefixes, or null
      * @return the elements which match the specified XPath expression
      * @see #getFirstByXPath(String)
      * @see #getCanonicalXPath()
      */
     public List<?> getByXPath(final String xpathExpr, final PrefixResolver resolver) {
         return XPathHelper.getByXPath(this, xpathExpr, resolver);
     }
 
     /**
      * Evaluates the specified XPath expression from this node, returning the first matching element,
      * or {@code null} if no node matches the specified XPath expression.
      *
      * @param xpathExpr the XPath expression
      * @param <X> the expression type
      * @return the first element matching the specified XPath expression
      * @see #getByXPath(String)
      * @see #getCanonicalXPath()
      */
     public <X> X getFirstByXPath(final String xpathExpr) {
         return getFirstByXPath(xpathExpr, null);
     }
 
     /**
      * Evaluates the specified XPath expression from this node, returning the first matching element,
      * or {@code null} if no node matches the specified XPath expression.
      *
      * @param xpathExpr the XPath expression
      * @param <X> the expression type
      * @param resolver the prefix resolver to use for resolving namespace prefixes, or null
      * @return the first element matching the specified XPath expression
      * @see #getByXPath(String)
      * @see #getCanonicalXPath()
      */
     @SuppressWarnings("unchecked")
     public <X> X getFirstByXPath(final String xpathExpr, final PrefixResolver resolver) {
         final List<?> results = getByXPath(xpathExpr, resolver);
         if (results.isEmpty()) {
             return null;
         }
         return (X) results.get(0);
     }
 
     /**
      * <p>Returns the canonical XPath expression which identifies this node, for instance
      * <code>"/html/body/table[3]/tbody/tr[5]/td[2]/span/a[3]"</code>.</p>
      *
      * <p><span style="color:red">WARNING:</span> This sort of automated XPath expression
      * is often quite bad at identifying a node, as it is highly sensitive to changes in
      * the DOM tree.</p>
      *
      * @return the canonical XPath expression which identifies this node
      * @see #getByXPath(String)
      */
     public String getCanonicalXPath() {
         throw new RuntimeException("Method getCanonicalXPath() not implemented for nodes of type " + getNodeType());
     }
 
     /**
      * Notifies the registered {@link IncorrectnessListener} of something that is not fully correct.
      * @param message the notification to send to the registered {@link IncorrectnessListener}
      */
     protected void notifyIncorrectness(final String message) {
         final WebClient client = getPage().getEnclosingWindow().getWebClient();
         final IncorrectnessListener incorrectnessListener = client.getIncorrectnessListener();
         incorrectnessListener.notify(message, this);
     }
 
     /**
      * Adds a {@link DomChangeListener} to the listener list. The listener is registered for
      * all descendants of this node.
      *
      * @param listener the DOM structure change listener to be added
      * @see #removeDomChangeListener(DomChangeListener)
      */
     public void addDomChangeListener(final DomChangeListener listener) {
         WebAssert.notNull("listener", listener);
 
         synchronized (this) {
             if (domListeners_ == null) {
                 domListeners_ = new ArrayList<>();
             }
             domListeners_.add(listener);
 
             final SgmlPage page = getPage();
             if (page != null) {
                 page.domChangeListenerAdded();
             }
         }
     }
 
     /**
      * Removes a {@link DomChangeListener} from the listener list. The listener is deregistered for
      * all descendants of this node.
      *
      * @param listener the DOM structure change listener to be removed
      * @see #addDomChangeListener(DomChangeListener)
      */
     public void removeDomChangeListener(final DomChangeListener listener) {
         WebAssert.notNull("listener", listener);
 
         synchronized (this) {
             if (domListeners_ != null) {
                 domListeners_.remove(listener);
             }
         }
     }
 
     /**
      * Support for reporting DOM changes. This method can be called when a node has been added, and it
      * will send the appropriate {@link DomChangeEvent} to any registered {@link DomChangeListener}s.
      *
      * <p>Note that this method recursively calls this node's parent's {@link #fireNodeAdded(DomNode, DomNode)}.</p>
      *
      * @param parentNode the parent of the node that was changed
      * @param addedNode the node that has been added
      */
     protected void fireNodeAdded(final DomNode parentNode, final DomNode addedNode) {
         DomChangeEvent event = null;
 
         DomNode toInform = this;
         while (toInform != null) {
             if (toInform.domListeners_ != null) {
                 final List<DomChangeListener> listeners;
                 synchronized (toInform) {
                     listeners = new ArrayList<>(toInform.domListeners_);
                 }
 
                 if (event == null) {
                     event = new DomChangeEvent(parentNode, addedNode);
                 }
                 for (final DomChangeListener domChangeListener : listeners) {
                     domChangeListener.nodeAdded(event);
                 }
             }
 
             toInform = toInform.getParentNode();
         }
     }
 
     /**
      * Adds a {@link CharacterDataChangeListener} to the listener list. The listener is registered for
      * all descendants of this node.
      *
      * @param listener the character data change listener to be added
      * @see #removeCharacterDataChangeListener(CharacterDataChangeListener)
      */
     public void addCharacterDataChangeListener(final CharacterDataChangeListener listener) {
         WebAssert.notNull("listener", listener);
 
         synchronized (this) {
             if (characterDataListeners_ == null) {
                 characterDataListeners_ = new ArrayList<>();
             }
             characterDataListeners_.add(listener);
 
             final SgmlPage page = getPage();
             if (page != null) {
                 page.characterDataChangeListenerAdded();
             }
         }
     }
 
     /**
      * Removes a {@link CharacterDataChangeListener} from the listener list. The listener is deregistered for
      * all descendants of this node.
      *
      * @param listener the Character Data change listener to be removed
      * @see #addCharacterDataChangeListener(CharacterDataChangeListener)
      */
     public void removeCharacterDataChangeListener(final CharacterDataChangeListener listener) {
         WebAssert.notNull("listener", listener);
 
         synchronized (this) {
             if (characterDataListeners_ != null) {
                 characterDataListeners_.remove(listener);
             }
         }
     }
 
     /**
      * Support for reporting Character Data changes.
      *
      * <p>Note that this method recursively calls this node's parent's {@link #fireCharacterDataChanged}.</p>
      *
      * @param characterData the character data which is changed
      * @param oldValue the old value
      */
     protected void fireCharacterDataChanged(final DomCharacterData characterData, final String oldValue) {
         CharacterDataChangeEvent event = null;
 
         DomNode toInform = this;
         while (toInform != null) {
             if (toInform.characterDataListeners_ != null) {
                 final List<CharacterDataChangeListener> listeners;
                 synchronized (toInform) {
                     listeners = new ArrayList<>(toInform.characterDataListeners_);
                 }
 
                 if (event == null) {
                     event = new CharacterDataChangeEvent(characterData, oldValue);
                 }
                 for (final CharacterDataChangeListener domChangeListener : listeners) {
                     domChangeListener.characterDataChanged(event);
                 }
             }
 
             toInform = toInform.getParentNode();
         }
     }
 
     /**
      * Support for reporting DOM changes. This method can be called when a node has been deleted, and it
      * will send the appropriate {@link DomChangeEvent} to any registered {@link DomChangeListener}s.
      *
      * <p>Note that this method recursively calls this node's parent's {@link #fireNodeDeleted(DomNode, DomNode)}.</p>
      *
      * @param parentNode the parent of the node that was changed
      * @param deletedNode the node that has been deleted
      */
     protected void fireNodeDeleted(final DomNode parentNode, final DomNode deletedNode) {
         DomChangeEvent event = null;
 
         DomNode toInform = this;
         while (toInform != null) {
             if (toInform.domListeners_ != null) {
                 final List<DomChangeListener> listeners;
                 synchronized (toInform) {
                     listeners = new ArrayList<>(toInform.domListeners_);
                 }
 
                 if (event == null) {
                     event = new DomChangeEvent(parentNode, deletedNode);
                 }
                 for (final DomChangeListener domChangeListener : listeners) {
                     domChangeListener.nodeDeleted(event);
                 }
             }
 
             toInform = toInform.getParentNode();
         }
     }
 
     /**
      * Retrieves all element nodes from descendants of the starting element node that match any selector
      * within the supplied selector strings.
      * @param selectors one or more CSS selectors separated by commas
      * @return list of all found nodes
      */
     public DomNodeList<DomNode> querySelectorAll(final String selectors) {
         try {
             final WebClient webClient = getPage().getWebClient();
             final SelectorList selectorList = getSelectorList(selectors, webClient);
 
             final List<DomNode> elements = new ArrayList<>();
             if (selectorList != null) {
                 for (final DomElement child : getDomElementDescendants()) {
                     for (final Selector selector : selectorList) {
                         if (CssStyleSheet.selects(webClient.getBrowserVersion(), selector, child, null, true, true)) {
                             elements.add(child);
                             break;
                         }
                     }
                 }
             }
             return new StaticDomNodeList(elements);
         }
         catch (final IOException e) {
             throw new CSSException("Error parsing CSS selectors from '" + selectors + "': " + e.getMessage(), e);
         }
     }
 
     /**
      * Returns the {@link SelectorList}.
      * @param selectors the selectors
      * @param webClient the {@link WebClient}
      * @return the {@link SelectorList}
      * @throws IOException if an error occurs
      */
     protected SelectorList getSelectorList(final String selectors, final WebClient webClient)
             throws IOException {
 
         // get us a CSS3Parser from the pool so the chance of reusing it are high
         try (PooledCSS3Parser pooledParser = webClient.getCSS3Parser()) {
             final CSSOMParser parser = new CSSOMParser(pooledParser);
             final CheckErrorHandler errorHandler = new CheckErrorHandler();
             parser.setErrorHandler(errorHandler);
 
             final SelectorList selectorList = parser.parseSelectors(selectors);
             // in case of error parseSelectors returns null
             if (errorHandler.error() != null) {
                 throw new CSSException("Invalid selectors: '" + selectors + "'", errorHandler.error());
             }
 
             if (selectorList != null) {
                 CssStyleSheet.validateSelectors(selectorList, this);
 
             }
             return selectorList;
         }
     }
 
     /**
      * Returns the first element within the document that matches the specified group of selectors.
      * @param selectors one or more CSS selectors separated by commas
      * @param <N> the node type
      * @return null if no matches are found; otherwise, it returns the first matching element
      */
     @SuppressWarnings("unchecked")
     public <N extends DomNode> N querySelector(final String selectors) {
         final DomNodeList<DomNode> list = querySelectorAll(selectors);
         if (!list.isEmpty()) {
             return (N) list.get(0);
         }
         return null;
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * Indicates if this node is currently attached to the page.
      * @return {@code true} if the page is one ancestor of the node.
      */
     public boolean isAttachedToPage() {
         return attachedToPage_;
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * Lifecycle method to support special processing for js method importNode.
      * @param doc the import target document
      * @see org.htmlunit.javascript.host.dom.Document#importNode(
      * org.htmlunit.javascript.host.dom.Node, boolean)
      * @see HtmlScript#processImportNode(org.htmlunit.javascript.host.dom.Document)
      */
     public void processImportNode(final org.htmlunit.javascript.host.dom.Document doc) {
         page_ = (SgmlPage) doc.getDomNodeOrDie();
     }
 
     /**
      * <span style="color:red">INTERNAL API - SUBJECT TO CHANGE AT ANY TIME - USE AT YOUR OWN RISK.</span><br>
      *
      * Helper for a common call sequence.
      * @param feature the feature to check
      * @return {@code true} if the currently emulated browser has this feature.
      */
     public boolean hasFeature(final BrowserVersionFeatures feature) {
         return getPage().getWebClient().getBrowserVersion().hasFeature(feature);
     }
 
     private static final class CheckErrorHandler implements CSSErrorHandler {
         private CSSParseException error_;
 
         CSSParseException error() {
             return error_;
         }
 
         @Override
         public void warning(final CSSParseException exception) throws CSSException {
             // ignore
         }
 
         @Override
         public void fatalError(final CSSParseException exception) throws CSSException {
             error_ = exception;
         }
 
         @Override
         public void error(final CSSParseException exception) throws CSSException {
             error_ = exception;
         }
     }
 
     /**
      * Indicates if the provided event can be applied to this node.
      * Overwrite this.
      * @param event the event
      * @return {@code false} if the event can't be applied
      */
     public boolean handles(final Event event) {
         return true;
     }
 
     /**
      * Returns the previous sibling element node of this element.
      * null if this element has no element sibling nodes that come before this one in the document tree.
      * @return the previous sibling element node of this element.
      *         null if this element has no element sibling nodes that come before this one in the document tree
      */
     public DomElement getPreviousElementSibling() {
         DomNode node = getPreviousSibling();
         while (node != null && !(node instanceof DomElement)) {
             node = node.getPreviousSibling();
         }
         return (DomElement) node;
     }
 
     /**
      * Returns the next sibling element node of this element.
      * null if this element has no element sibling nodes that come after this one in the document tree.
      * @return the next sibling element node of this element.
      *         null if this element has no element sibling nodes that come after this one in the document tree
      */
     public DomElement getNextElementSibling() {
         DomNode node = getNextSibling();
         while (node != null && !(node instanceof DomElement)) {
             node = node.getNextSibling();
         }
         return (DomElement) node;
     }
 
     /**
      * @param selectorString the selector to test
      * @return the selected {@link DomElement} or null.
      */
     public DomElement closest(final String selectorString) {
         try {
             final WebClient webClient = getPage().getWebClient();
             final SelectorList selectorList = getSelectorList(selectorString, webClient);
 
             DomNode current = this;
             if (selectorList != null) {
                 do {
                     for (final Selector selector : selectorList) {
                         final DomElement elem = (DomElement) current;
                         if (CssStyleSheet.selects(webClient.getBrowserVersion(), selector, elem, null, true, true)) {
                             return elem;
                         }
                     }
 
                     do {
                         current = current.getParentNode();
                     }
                     while (current != null && !(current instanceof DomElement));
                 }
                 while (current != null);
             }
             return null;
         }
         catch (final IOException e) {
             throw new CSSException("Error parsing CSS selectors from '" + selectorString + "': " + e.getMessage(), e);
         }
     }
 
     /**
      * An unmodifiable empty {@link NamedNodeMap} implementation.
      */
     private static final class ReadOnlyEmptyNamedNodeMapImpl implements NamedNodeMap, Serializable {
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int getLength() {
             return 0;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public DomAttr getNamedItem(final String name) {
             return null;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public Node getNamedItemNS(final String namespaceURI, final String localName) {
             return null;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public Node item(final int index) {
             return null;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public Node removeNamedItem(final String name) throws DOMException {
             return null;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public Node removeNamedItemNS(final String namespaceURI, final String localName) {
             return null;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public DomAttr setNamedItem(final Node node) {
             throw new UnsupportedOperationException("ReadOnlyEmptyNamedAttrNodeMapImpl.setNamedItem");
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public Node setNamedItemNS(final Node node) throws DOMException {
             throw new UnsupportedOperationException("ReadOnlyEmptyNamedAttrNodeMapImpl.setNamedItemNS");
         }
     }
 }