docs: private XmlElemRef xmlElemRef(int atPos, Name namespace, int colonPos)
          throws IOException
      {
          int lb = ts.tokenBeg, rb = -1, pos = atPos != -1 ? atPos : lb;
          AstNode expr = expr();
          int end = getNodeEnd(expr);
          if (mustMatchToken(Token.RB, "msg.no.bracket.index", true)) {
              rb = ts.tokenBeg;
              end = ts.tokenEnd;
          }
          XmlElemRef ref = new XmlElemRef(pos, end - pos);
          ref.setNamespace(namespace);
          ref.setColonPos(colonPos);
          ref.setAtPos(atPos);
          ref.setExpression(expr);
          ref.setBrackets(lb, rb);
          return ref;
      }