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;


EntityReference nodes may be used to represent an entity 
reference in the tree. Note that character references and references to 
predefined entities are considered to be expanded by the HTML or XML 
processor so that characters are represented by their Unicode equivalent 
rather than by an entity reference. Moreover, the XML processor may 
completely expand references to entities while building the 
Document, instead of providing EntityReference 
nodes. If it does provide such nodes, then for an 
EntityReference node that represents a reference to a known 
entity an Entity exists, and the subtree of the 
EntityReference node is a copy of the Entity 
node subtree. However, the latter may not be true when an entity contains 
an unbound namespace prefix. In such a case, because the namespace prefix 
resolution depends on where the entity reference is, the descendants of 
the EntityReference node may be bound to different namespace 
URIs. When an EntityReference node represents a reference to 
an unknown entity, the node has no children and its replacement value, 
when used by Attr.value for example, is empty.

As for Entity nodes, EntityReference nodes and 
all their descendants are readonly.

Note: EntityReference nodes may cause element 
content and attribute value normalization problems when, such as in XML 
1.0 and XML Schema, the normalization is performed after entity reference 
are expanded.

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

/**
 * <code>EntityReference</code> nodes may be used to represent an entity 
 * reference in the tree. Note that character references and references to 
 * predefined entities are considered to be expanded by the HTML or XML 
 * processor so that characters are represented by their Unicode equivalent 
 * rather than by an entity reference. Moreover, the XML processor may 
 * completely expand references to entities while building the 
 * <code>Document</code>, instead of providing <code>EntityReference</code> 
 * nodes. If it does provide such nodes, then for an 
 * <code>EntityReference</code> node that represents a reference to a known 
 * entity an <code>Entity</code> exists, and the subtree of the 
 * <code>EntityReference</code> node is a copy of the <code>Entity</code> 
 * node subtree. However, the latter may not be true when an entity contains 
 * an unbound namespace prefix. In such a case, because the namespace prefix 
 * resolution depends on where the entity reference is, the descendants of 
 * the <code>EntityReference</code> node may be bound to different namespace 
 * URIs. When an <code>EntityReference</code> node represents a reference to 
 * an unknown entity, the node has no children and its replacement value, 
 * when used by <code>Attr.value</code> for example, is empty.
 * <p>As for <code>Entity</code> nodes, <code>EntityReference</code> nodes and 
 * all their descendants are readonly.
 * <p ><b>Note:</b> <code>EntityReference</code> nodes may cause element 
 * content and attribute value normalization problems when, such as in XML 
 * 1.0 and XML Schema, the normalization is performed after entity reference 
 * are expanded.
 * <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>.
 */
public interface EntityReference extends Node {
}