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) 2004 World Wide Web Consortium,
 *
 * (Massachusetts Institute of Technology, European Research Consortium for
 * Informatics and Mathematics, Keio University). All Rights Reserved. This
 * work is distributed under the W3C(r) Software License [1] 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.
 *
 * [1] http://www.w3.org/Consortium/Legal/2002/copyright-software-20021231
 */

package org.w3c.dom;


 The DOMImplementationList interface provides the abstraction 
of an ordered collection of DOM implementations, without defining or 
constraining how this collection is implemented. The items in the 
DOMImplementationList are accessible via an integral index, 
starting from 0. 

See also the Document Object Model (DOM) Level 3 Core Specification.

Since:DOM Level 3
/**
 *  The <code>DOMImplementationList</code> interface provides the abstraction 
 * of an ordered collection of DOM implementations, without defining or 
 * constraining how this collection is implemented. The items in the 
 * <code>DOMImplementationList</code> are accessible via an integral index, 
 * starting from 0. 
 * <p>See also the <a href='http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407'>Document Object Model (DOM) Level 3 Core Specification</a>.
 * @since DOM Level 3
 */
public interface DOMImplementationList {
    
 Returns the indexth item in the collection. If 
index is greater than or equal to the number of 
DOMImplementations in the list, this returns 
null. 

Params:
  • index – Index into the collection.
Returns: The DOMImplementation at the index
  th position in the DOMImplementationList, or 
  null if that is not a valid index.
/**
     *  Returns the <code>index</code>th item in the collection. If 
     * <code>index</code> is greater than or equal to the number of 
     * <code>DOMImplementation</code>s in the list, this returns 
     * <code>null</code>. 
     * @param index Index into the collection.
     * @return  The <code>DOMImplementation</code> at the <code>index</code>
     *   th position in the <code>DOMImplementationList</code>, or 
     *   <code>null</code> if that is not a valid index. 
     */
    public DOMImplementation item(int index);

    
 The number of DOMImplementations in the list. The range 
of valid child node indices is 0 to length-1 inclusive. 

/**
     *  The number of <code>DOMImplementation</code>s in the list. The range 
     * of valid child node indices is 0 to <code>length-1</code> inclusive. 
     */
    public int getLength();

}