docs: private String tryEncodingDecl(String encoding) throws SAXException,
              IOException {
          // Read the XML/text declaration.
          if (tryRead("<?xml")) {
              if (tryWhitespace()) {
                  if (inputStack.size() > 0) {
                      return parseTextDecl(encoding);
                  } else {
                      return parseXMLDecl(encoding);
                  }
              } else {
                  // <?xml-stylesheet ...?> or similar
                  pushString(null, "<?xml");
  //                unread('l');
  //                unread('m');
  //                unread('x');
  //                unread('?');
  //                unread('<');
              }
          }
          // 2006-02-03 hsivonen
          warnAboutLackOfEncodingDecl(encoding);
          return null;
      }