* a Map, or an instance of a specified class.
 * </p>
 *
 * <p>
 * Example usage:
 * </p>
 *
 * <pre>
 * XpathTransformer transformer = new XpathTransformer();
 * transformer.addFieldRule("title", "//title/text()");
 * transformer.addFieldRule("body", "//body/p/text()");
 *
 * ResponseData responseData = new ResponseData();

 * </p>
 *
 * <pre>
 * XmlTransformer transformer = new XmlTransformer();
 * transformer.setNamespaceAware(true);
 * transformer.setCacheDuration(30);
 * transformer.addFieldRule("title", "/book/title/text()");
 * transformer.addFieldRule("author", "/book/author/name/text()");
 *
 * ResponseData responseData = new ResponseData();