You might find yourself trying to implement a custom file browser with ckeditor.
You might also find yourself attempting to send the URL of the selected file back to Ckeditor.
You should have come accross this somewhere:
window.CKEDITOR.tools.callFunction(< insert CKEditorFuncNum here >, selectedFileUrl);
You will be thrilled to find out that CKeditor attaches that number to the instance of itself.
To get that function number:
window.CKEDITOR.instances[ yourInstance ]._.filebrowserFn
Violla!
All your problems are solved.
Finished Code: (my ckeditor instance is called ckeditor)
window.CKEDITOR.tools.callFunction(window.CKEDITOR.instances.ckeditor._.filebrowserFn, selectedFileUrl);