code: function () {
  
          var me = this,
              activeError = me.getActiveError(),
              hasError = !!activeError;
  
          var edTable = Ext.get(me.getInputId() + "_tbl");
          var edIframe = Ext.get(me.getInputId() + "_ifr");
  
          if (!edTable) { return me.callParent(arguments); }
  
          /*
           Adding the red border to the mceIframeContainer is the most sure
           way to do it without harming sizing and positioning.
           */
          var edFrameContainer = edTable.down(".mceIframeContainer");
  
          if (edFrameContainer && me.rendered && !me.isDestroyed && !me.preventMark) {
              var ed = tinymce.get(me.getInputId());
  
              var evHandler = function (ed, e) {
                  me.clearInvalid();
              };
  
              // Add/remove invalid class
              if (hasError) {
                  edFrameContainer.addCls('tinymce-error-field');
  
                  // this dirty hack is required for WebKit browsers - Safari and Chrome
                  edIframe.setHeight(edIframe.getHeight() - 1);
                  edIframe.setHeight(edIframe.getHeight() + 1);
  
                  if (ed) {
                      // the invalid mark should be removed after any
                      // change of the contents (ExtJS standard behaviour)
                      ed.onKeyDown.add(evHandler);
                  }
              }
              else {
                  edFrameContainer.removeCls('tinymce-error-field');
  
                  // this dirty hack is required for WebKit browsers - Safari and Chrome
                  edIframe.setHeight(edIframe.getHeight() - 1);
                  edIframe.setHeight(edIframe.getHeight() + 1);
  
                  if (ed) {
                      ed.onKeyDown.remove(evHandler);
                      ed.onChange.remove(evHandler);
                  }
              }
          }
  
          return me.callParent(arguments);
      }
docs: -----------------------------------------------------------------