InputSource getExternalSubset(String name, String baseURI)
            throws SAXException, IOException {
        if (resolver2 == null || !useResolver2 || !extPE) {
            return null;
        }
        return resolver2.getExternalSubset(name, baseURI);
    }
<b>SAX2</b>: Assigns the specified property. Like SAX1 handlers, these
may be changed at any time.
src/nu/validator/gnu/xml/aelfred2/SAXDriver.java