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.xpath;


The XPathNSResolver interface permit prefix 
strings in the expression to be properly bound to 
namespaceURI strings. XPathEvaluator can 
construct an implementation of XPathNSResolver from a node, 
or the interface may be implemented by any application.

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

/**
 * The <code>XPathNSResolver</code> interface permit <code>prefix</code> 
 * strings in the expression to be properly bound to 
 * <code>namespaceURI</code> strings. <code>XPathEvaluator</code> can 
 * construct an implementation of <code>XPathNSResolver</code> from a node, 
 * or the interface may be implemented by any application.
 * <p>See also the <a href='http://www.w3.org/TR/2004/NOTE-DOM-Level-3-XPath-20040226'>Document Object Model (DOM) Level 3 XPath Specification</a>.
 */
public interface XPathNSResolver {
    
Look up the namespace URI associated to the given namespace prefix. The 
XPath evaluator must never call this with a null or 
empty argument, because the result of doing this is undefined.

Params:
  • prefix – The prefix to look for.
Returns:Returns the associated namespace URI or null if 
  none is found.
/**
     * Look up the namespace URI associated to the given namespace prefix. The 
     * XPath evaluator must never call this with a <code>null</code> or 
     * empty argument, because the result of doing this is undefined.
     * @param prefix The prefix to look for.
     * @return Returns the associated namespace URI or <code>null</code> if 
     *   none is found.
     */
    public String lookupNamespaceURI(String prefix);

}