Retrieving the current instance from a child plugin popup ?

If there are SEVERAL instances of the editor on the same page..

How to retrieve, from a plugin popup window, the current instance of the editor, if there are several instances of CKEditor on the same page ?

I'm trying in the popup child window:

alert(window.opener.CKEDITOR); alert(window.opener.CKEDITOR.currentInstance); var currentEditor = window.opener.CKEDITOR.currentInstance; var selectedContent = currentEditor._.selectedContent; currentEditor.insertHtml('Some content");

but the second alert is null.