title: custom XML part is getting replaced in co-authoring mode
body: <p>I'm using <code>onedrive for business</code> for co-authoring the document, provided that, My document contains customXML, which is mapped with document object.</p>
  <p>Now, when two user edits the plain text, their changes are saved in real-time. But when user edits the CustomXML (which is mapped with document), one whose changes are saved at last will replace the changes saved previously.</p>
  <p>Technically, changes in document.xml are saved in real time or we must say that the document.xml of two users are getting merged but the customXML are getting completely replaced, instead, they should be merged.</p>
  <p>Can anyone help me that how to support the co-authoring of content control?</p>
  <p>Thanks in advance</p>