http://xml.apache.org/commons/components/external/: xml-commons provides an Apache-hosted set of DOM, SAX, and JAXP interfaces for use in other xml-based projects. Our hope is that we can standardize on both a common version and packaging scheme for these critical XML standards interfaces to make the lives of both our developers and users easier. The External Components portion of xml-commons contains interfaces that are defined by external standards organizations. For DOM, that's the W3C; for SAX it's David Megginson and sax.sourceforge.net; for JAXP it's Sun. 
/*
 * 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;


Filters are objects that know how to "filter out" nodes. If a 
NodeIterator or TreeWalker is given a 
NodeFilter, it applies the filter before it returns the next 
node. If the filter says to accept the node, the traversal logic returns 
it; otherwise, traversal looks for the next node and pretends that the 
node that was rejected was not there.

The DOM does not provide any filters. NodeFilter is just an 
interface that users can implement to provide their own filters. 

NodeFilters do not need to know how to traverse from node 
to node, nor do they need to know anything about the data structure that 
is being traversed. This makes it very easy to write filters, since the 
only thing they have to know how to do is evaluate a single node. One 
filter may be used with a number of different kinds of traversals, 
encouraging code reuse.

See also the Document Object Model (DOM) Level 2 Traversal and Range Specification.

Since:DOM Level 2
/**
 * Filters are objects that know how to "filter out" nodes. If a 
 * <code>NodeIterator</code> or <code>TreeWalker</code> is given a 
 * <code>NodeFilter</code>, it applies the filter before it returns the next 
 * node. If the filter says to accept the node, the traversal logic returns 
 * it; otherwise, traversal looks for the next node and pretends that the 
 * node that was rejected was not there.
 * <p>The DOM does not provide any filters. <code>NodeFilter</code> is just an 
 * interface that users can implement to provide their own filters. 
 * <p><code>NodeFilters</code> do not need to know how to traverse from node 
 * to node, nor do they need to know anything about the data structure that 
 * is being traversed. This makes it very easy to write filters, since the 
 * only thing they have to know how to do is evaluate a single node. One 
 * filter may be used with a number of different kinds of traversals, 
 * encouraging code reuse.
 * <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 NodeFilter {
    // Constants returned by acceptNode
    
Accept the node. Navigation methods defined for 
NodeIterator or TreeWalker will return this 
node.

/**
     * Accept the node. Navigation methods defined for 
     * <code>NodeIterator</code> or <code>TreeWalker</code> will return this 
     * node.
     */
    public static final short FILTER_ACCEPT             = 1;
    
Reject the node. Navigation methods defined for 
NodeIterator or TreeWalker will not return 
this node. For TreeWalker, the children of this node 
will also be rejected. NodeIterators treat this as a 
synonym for FILTER_SKIP.

/**
     * Reject the node. Navigation methods defined for 
     * <code>NodeIterator</code> or <code>TreeWalker</code> will not return 
     * this node. For <code>TreeWalker</code>, the children of this node 
     * will also be rejected. <code>NodeIterators</code> treat this as a 
     * synonym for <code>FILTER_SKIP</code>.
     */
    public static final short FILTER_REJECT             = 2;
    
Skip this single node. Navigation methods defined for 
NodeIterator or TreeWalker will not return 
this node. For both NodeIterator and 
TreeWalker, the children of this node will still be 
considered. 

/**
     * Skip this single node. Navigation methods defined for 
     * <code>NodeIterator</code> or <code>TreeWalker</code> will not return 
     * this node. For both <code>NodeIterator</code> and 
     * <code>TreeWalker</code>, the children of this node will still be 
     * considered. 
     */
    public static final short FILTER_SKIP               = 3;

    // Constants for whatToShow
    
Show all Nodes.

/**
     * Show all <code>Nodes</code>.
     */
    public static final int SHOW_ALL                  = 0xFFFFFFFF;
    
Show Element nodes.

/**
     * Show <code>Element</code> nodes.
     */
    public static final int SHOW_ELEMENT              = 0x00000001;
    
Show Attr nodes. This is meaningful only when creating an 
NodeIterator or TreeWalker with an 
attribute node as its root; in this case, it means that 
the attribute node will appear in the first position of the iteration 
or traversal. Since attributes are never children of other nodes, 
they do not appear when traversing over the document tree.

/**
     * Show <code>Attr</code> nodes. This is meaningful only when creating an 
     * <code>NodeIterator</code> or <code>TreeWalker</code> with an 
     * attribute node as its <code>root</code>; in this case, it means that 
     * the attribute node will appear in the first position of the iteration 
     * or traversal. Since attributes are never children of other nodes, 
     * they do not appear when traversing over the document tree.
     */
    public static final int SHOW_ATTRIBUTE            = 0x00000002;
    
Show Text nodes.

/**
     * Show <code>Text</code> nodes.
     */
    public static final int SHOW_TEXT                 = 0x00000004;
    
Show CDATASection nodes.

/**
     * Show <code>CDATASection</code> nodes.
     */
    public static final int SHOW_CDATA_SECTION        = 0x00000008;
    
Show EntityReference nodes.

/**
     * Show <code>EntityReference</code> nodes.
     */
    public static final int SHOW_ENTITY_REFERENCE     = 0x00000010;
    
Show Entity nodes. This is meaningful only when creating 
an NodeIterator or TreeWalker with an 
Entity node as its root; in this case, it 
means that the Entity node will appear in the first 
position of the traversal. Since entities are not part of the 
document tree, they do not appear when traversing over the document 
tree.

/**
     * Show <code>Entity</code> nodes. This is meaningful only when creating 
     * an <code>NodeIterator</code> or <code>TreeWalker</code> with an 
     * <code>Entity</code> node as its <code>root</code>; in this case, it 
     * means that the <code>Entity</code> node will appear in the first 
     * position of the traversal. Since entities are not part of the 
     * document tree, they do not appear when traversing over the document 
     * tree.
     */
    public static final int SHOW_ENTITY               = 0x00000020;
    
Show ProcessingInstruction nodes.

/**
     * Show <code>ProcessingInstruction</code> nodes.
     */
    public static final int SHOW_PROCESSING_INSTRUCTION = 0x00000040;
    
Show Comment nodes.

/**
     * Show <code>Comment</code> nodes.
     */
    public static final int SHOW_COMMENT              = 0x00000080;
    
Show Document nodes.

/**
     * Show <code>Document</code> nodes.
     */
    public static final int SHOW_DOCUMENT             = 0x00000100;
    
Show DocumentType nodes.

/**
     * Show <code>DocumentType</code> nodes.
     */
    public static final int SHOW_DOCUMENT_TYPE        = 0x00000200;
    
Show DocumentFragment nodes.

/**
     * Show <code>DocumentFragment</code> nodes.
     */
    public static final int SHOW_DOCUMENT_FRAGMENT    = 0x00000400;
    
Show Notation nodes. This is meaningful only when creating 
an NodeIterator or TreeWalker with a 
Notation node as its root; in this case, it 
means that the Notation node will appear in the first 
position of the traversal. Since notations are not part of the 
document tree, they do not appear when traversing over the document 
tree.

/**
     * Show <code>Notation</code> nodes. This is meaningful only when creating 
     * an <code>NodeIterator</code> or <code>TreeWalker</code> with a 
     * <code>Notation</code> node as its <code>root</code>; in this case, it 
     * means that the <code>Notation</code> node will appear in the first 
     * position of the traversal. Since notations are not part of the 
     * document tree, they do not appear when traversing over the document 
     * tree.
     */
    public static final int SHOW_NOTATION             = 0x00000800;

    
Test whether a specified node is visible in the logical view of a 
TreeWalker or NodeIterator. This function 
will be called by the implementation of TreeWalker and 
NodeIterator; it is not normally called directly from 
user code. (Though you could do so if you wanted to use the same 
filter to guide your own application logic.)

Params:
  • n – The node to check to see if it passes the filter or not.
Returns:A constant to determine whether the node is accepted, 
  rejected, or skipped, as defined above.
/**
     * Test whether a specified node is visible in the logical view of a 
     * <code>TreeWalker</code> or <code>NodeIterator</code>. This function 
     * will be called by the implementation of <code>TreeWalker</code> and 
     * <code>NodeIterator</code>; it is not normally called directly from 
     * user code. (Though you could do so if you wanted to use the same 
     * filter to guide your own application logic.)
     * @param n The node to check to see if it passes the filter or not.
     * @return A constant to determine whether the node is accepted, 
     *   rejected, or skipped, as defined above.
     */
    public short acceptNode(Node n);

}