code: public void renderView(ServletRequest request, ServletResponse response, ServletContext servletContext)
              throws IOException
      {
          ResponseRenderAppender appender = new ResponseRenderAppender(response);
          ScriptTag.State state = new ScriptTag.State();
          ScriptTag br = (ScriptTag) TagRenderingBase.Factory.getRendering(TagRenderingBase.SCRIPT_TAG, request);
          state.suppressComments = false;
          br.doStartTag(appender, state);
  
          appender.append(ScriptRequestState.getString("popupReturn_begin", null));
          assert request instanceof HttpServletRequest : request.getClass().getName();
          HttpServletRequest httpRequest = (HttpServletRequest) request;
  
          if (_retrieveMap != null) {
              for (Iterator/*<Map.Entry>*/ i = _retrieveMap.entrySet().iterator(); i.hasNext();) {
                  Map.Entry entry = (Map.Entry) i.next();
                  String fieldID = (String) entry.getKey();
                  String expressionToRetrieve = "${" + (String) entry.getValue() + '}';
                  try {
                      String value =
                              InternalExpressionUtils.evaluateMessage(expressionToRetrieve, null, httpRequest, servletContext);
                      String item =
                              ScriptRequestState.getString("popupReturn_item", new Object[]{fieldID, value});
                      appender.append(item);
                  }
                  catch (ELException e) {
                      _log.error("Error evaluating expression " + expressionToRetrieve, e);
                  }
              }
          }
  
          appender.append(ScriptRequestState.getString("popupReturn_end", new Object[]{_callbackFunc}));
          br.doEndTag(appender, false);
      }
docs: Render the JavaScript for this framework response to a popup window.
  The JavaScript passes a map of field values from the popup back to
  a JavaScript routine on the originating page updating its form fields.
  (See {@link org.apache.beehive.netui.tags.html.ConfigurePopup})
  The javascript also closes the popup window.