 in xml-commons in order to add classpath entity
 and URI resolution.  Since XMLCatalog already does classpath
 resolution, we simply add all CatalogEntry instances back to the
 controlling XMLCatalog instance.  This is done via a callback
 mechanism.  ApacheCatalog is <em>only</em> used for external
 catalog files.  Inline entries (currently <code>&lt;dtd&gt;</code>
 and <code>&lt;entity&gt;</code>) are not added to ApacheCatalog.
 See XMLCatalog.java for the details of the entity and URI
 resolution algor