public void actionPerformed(ActionEvent e) {
String selected = (String) cell.getUserObject();
XQExpression expr = sourceExprMap.get(selected);
DynamicContext dynEnv = new DynamicContext(statEnv);
StringWriter sw = new StringWriter();
SAXSerializer ser = new SAXSerializer(new SAXWriter(sw), sw);
try {
expr.evalAsEvents(ser, ValueSequence.EMPTY_SEQUENCE, dynEnv);
} catch (Exception ex) {
JOptionPane.showMessageDialog(frame, "eval failed!: " + ex.getMessage());
ex.printStackTrace();