Steps to Reproduce

http://zkfiddle.org/sample/2rvbcep/1-ckeditor-modal-close-iframe-destroy

Click the close button on the modal window.

Current Result

the iframe DOM element (not ZK iframe component) included in the Editor DOM tree is removed by the window modal onClose workflow.
This cause a warning in the console.

Expected Result

ZK should only remove ZK based iframes from the DOM

Debug Info

The editor DOM is detroyed before the editor JS object is destroyed during widget.unbind_
This causes a warning in the client console:
[CKEDITOR] Error code: editor-destroy-iframe.
(anonymous)
[CKEDITOR] For more information about this error go to http://docs.ckeditor.com/#!/guide/dev_errors-section-editor-destroy-iframe

This behavior prevents ZK iframes components from being reloaded when moved around the DOM tree. However, it also affects non-ZK iframes.

Root Cause

Affect window and panel:
Window:
https://github.com/zkoss/zk/blob/master/zul/src/archive/web/js/zul/wnd/Window.js#L1166
https://github.com/zkoss/zk/blob/master/zul/src/archive/web/js/zul/wnd/Window.js#L1203

Also in panel:
https://github.com/zkoss/zk/blob/master/zul/src/archive/web/js/zul/wnd/Panel.js#L868

Workaround

<script><![CDATA[
		zk.afterLoad('zul.wnd', function() {
			var xWindow = {};
			zk.override(zul.wnd.Window.prototype, xWindow ,{
				onClose : function() {
					this.$n().querySelectorAll(".z-ckeditor").forEach(function(elem){
						zk.$(elem)._editor.destroy(true);
						delete zk.$(elem)._editor;
					});
					var result = xWindow.onClose.apply(this, arguments);
					return result;
				}
			});//zk.override
		});//zk.afterLoad
	]]></script>