boolean valid = true;
DocType doctype = document.getDocType();
if (doctype == null) {
valid = false;
}
else {
// check doctype
}
Element root = document.getRootElement();
String uri = root.getNamespaceURI();
String prefix = root.getNamespacePrefix();
if (!uri.equals("http://www.w3.org/1999/xhtml")) {
valid = false;
}
if (!prefix.equals("")) valid = false;