title: How to change an already registered dialog in CKEditor
body: <p>I'm trying to write a plugin, that adds an additional tab (page) to the image dialog. I don't want to change the dialog's source itself, but enhance it with the plugin.</p>
  
  <p>I searched the docs and the forum for quite some time now, and I now know that I can call "addPage" on the dialogs object to add another tab. I also understand how the contents object must look like.
  But I failed in finding the way how to get the dialog object of an already existing dialog.</p>
  
  <p>I tried a</p>
  
  <pre><code>var ImageDialog = new CKEDITOR.dialog( editor, 'image' );
  </code></pre>
  
  <p>within the plugin's init method, but that caused an JS error "R is not a function"...</p>
  
  <p>Can somebody help me out here, please?</p>
  
  <p>Thanks in advance,
  Marc</p>