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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file and, per its terms, should not be removed:
 *
 * Copyright (c) 2000 World Wide Web Consortium,
 * (Massachusetts Institute of Technology, Institut National de
 * Recherche en Informatique et en Automatique, Keio University). All
 * Rights Reserved. This program is distributed under the W3C's Software
 * Intellectual Property License. This program is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY; without even
 * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 * PURPOSE.
 * See W3C License http://www.w3.org/Consortium/Legal/ for more details.
 */

package org.w3c.dom.traversal;

import org.w3c.dom.Node;
import org.w3c.dom.DOMException;

/**
 * <code>TreeWalker</code> objects are used to navigate a document tree or
 * subtree using the view of the document defined by their
 * <code>whatToShow</code> flags and filter (if any). Any function which
 * performs navigation using a <code>TreeWalker</code> will automatically
 * support any view defined by a <code>TreeWalker</code>.
 * <p>Omitting nodes from the logical view of a subtree can result in a
 * structure that is substantially different from the same subtree in the
 * complete, unfiltered document. Nodes that are siblings in the
 * <code>TreeWalker</code> view may be children of different, widely
 * separated nodes in the original view. For instance, consider a
 * <code>NodeFilter</code> that skips all nodes except for Text nodes and
 * the root node of a document. In the logical view that results, all text
 * nodes will be siblings and appear as direct children of the root node, no
 * matter how deeply nested the structure of the original document.
 * <p>See also the <a href='http://www.w3.org/TR/2000/REC-DOM-Level-2-Traversal-Range-20001113'>Document Object Model (DOM) Level 2 Traversal and Range Specification</a>.
 * @since DOM Level 2
 */
public interface TreeWalker {
    /**
     * The <code>root</code> node of the <code>TreeWalker</code>, as specified
     * when it was created.
     */
    public Node getRoot();

    /**
     * This attribute determines which node types are presented via the
     * <code>TreeWalker</code>. The available set of constants is defined in
     * the <code>NodeFilter</code> interface.  Nodes not accepted by
     * <code>whatToShow</code> will be skipped, but their children may still
     * be considered. Note that this skip takes precedence over the filter,
     * if any.
     */
    public int getWhatToShow();

    /**
     * The filter used to screen nodes.
     */
    public NodeFilter getFilter();

    /**
     * The value of this flag determines whether the children of entity
     * reference nodes are visible to the <code>TreeWalker</code>. If false,
     * these children  and their descendants will be rejected. Note that
     * this rejection takes precedence over <code>whatToShow</code> and the
     * filter, if any.
     * <br> To produce a view of the document that has entity references
     * expanded and does not expose the entity reference node itself, use
     * the <code>whatToShow</code> flags to hide the entity reference node
     * and set <code>expandEntityReferences</code> to true when creating the
     * <code>TreeWalker</code>. To produce a view of the document that has
     * entity reference nodes but no entity expansion, use the
     * <code>whatToShow</code> flags to show the entity reference node and
     * set <code>expandEntityReferences</code> to false.
     */
    public boolean getExpandEntityReferences();

    /**
     * The node at which the <code>TreeWalker</code> is currently positioned.
     * <br>Alterations to the DOM tree may cause the current node to no longer
     * be accepted by the <code>TreeWalker</code>'s associated filter.
     * <code>currentNode</code> may also be explicitly set to any node,
     * whether or not it is within the subtree specified by the
     * <code>root</code> node or would be accepted by the filter and
     * <code>whatToShow</code> flags. Further traversal occurs relative to
     * <code>currentNode</code> even if it is not part of the current view,
     * by applying the filters in the requested direction; if no traversal
     * is possible, <code>currentNode</code> is not changed.
     */
    public Node getCurrentNode();
    /**
     * The node at which the <code>TreeWalker</code> is currently positioned.
     * <br>Alterations to the DOM tree may cause the current node to no longer
     * be accepted by the <code>TreeWalker</code>'s associated filter.
     * <code>currentNode</code> may also be explicitly set to any node,
     * whether or not it is within the subtree specified by the
     * <code>root</code> node or would be accepted by the filter and
     * <code>whatToShow</code> flags. Further traversal occurs relative to
     * <code>currentNode</code> even if it is not part of the current view,
     * by applying the filters in the requested direction; if no traversal
     * is possible, <code>currentNode</code> is not changed.
     * @exception DOMException
     *   NOT_SUPPORTED_ERR: Raised if an attempt is made to set
     *   <code>currentNode</code> to <code>null</code>.
     */
    public void setCurrentNode(Node currentNode)
                         throws DOMException;

    /**
     * Moves to and returns the closest visible ancestor node of the current
     * node. If the search for <code>parentNode</code> attempts to step
     * upward from the <code>TreeWalker</code>'s <code>root</code> node, or
     * if it fails to find a visible ancestor node, this method retains the
     * current position and returns <code>null</code>.
     * @return The new parent node, or <code>null</code> if the current node
     *   has no parent  in the <code>TreeWalker</code>'s logical view.
     */
    public Node parentNode();

    /**
     * Moves the <code>TreeWalker</code> to the first visible child of the
     * current node, and returns the new node. If the current node has no
     * visible children, returns <code>null</code>, and retains the current
     * node.
     * @return The new node, or <code>null</code> if the current node has no
     *   visible children  in the <code>TreeWalker</code>'s logical view.
     */
    public Node firstChild();

    /**
     * Moves the <code>TreeWalker</code> to the last visible child of the
     * current node, and returns the new node. If the current node has no
     * visible children, returns <code>null</code>, and retains the current
     * node.
     * @return The new node, or <code>null</code> if the current node has no
     *   children  in the <code>TreeWalker</code>'s logical view.
     */
    public Node lastChild();

    /**
     * Moves the <code>TreeWalker</code> to the previous sibling of the
     * current node, and returns the new node. If the current node has no
     * visible previous sibling, returns <code>null</code>, and retains the
     * current node.
     * @return The new node, or <code>null</code> if the current node has no
     *   previous sibling.  in the <code>TreeWalker</code>'s logical view.
     */
    public Node previousSibling();

    /**
     * Moves the <code>TreeWalker</code> to the next sibling of the current
     * node, and returns the new node. If the current node has no visible
     * next sibling, returns <code>null</code>, and retains the current node.
     * @return The new node, or <code>null</code> if the current node has no
     *   next sibling.  in the <code>TreeWalker</code>'s logical view.
     */
    public Node nextSibling();

    /**
     * Moves the <code>TreeWalker</code> to the previous visible node in
     * document order relative to the current node, and returns the new
     * node. If the current node has no previous node,  or if the search for
     * <code>previousNode</code> attempts to step upward from the
     * <code>TreeWalker</code>'s <code>root</code> node,  returns
     * <code>null</code>, and retains the current node.
     * @return The new node, or <code>null</code> if the current node has no
     *   previous node  in the <code>TreeWalker</code>'s logical view.
     */
    public Node previousNode();

    /**
     * Moves the <code>TreeWalker</code> to the next visible node in document
     * order relative to the current node, and returns the new node. If the
     * current node has no next node, or if the search for nextNode attempts
     * to step upward from the <code>TreeWalker</code>'s <code>root</code>
     * node, returns <code>null</code>, and retains the current node.
     * @return The new node, or <code>null</code> if the current node has no
     *   next node  in the <code>TreeWalker</code>'s logical view.
     */
    public Node nextNode();

}
