Sub testxmladd()
Dim i As Long
  For i = ActiveDocument.CustomXMLParts.Count To 4 Step -1
     ActiveDocument.CustomXMLParts(i).Delete
  Next
  'Add a part with Prefixed namespace:
  ActiveDocument.CustomXMLParts.Add XML:= _
        "<RCDP xmlns:a=""https://www.w3schools.com/furniture"">" & _
        "<a:arcprop id=""HeadingVisibilityP"">" & _
        "<a:visibility>True</a:visibility>" & _
        "<a:enabled>True</a:enabled>" & _
        "</a:arcprop>" & _
        "<a:arcprop id= ""HeadingVisibilityS"">" & _
        "<a:visibility>False</a:visibility>" & _
        "<a:checked>True></a:checked>" & _
        "</a:arcprop>" & _
        "</RCDP>"
  'Add a part with unprefixed namespace.
  ActiveDocument.CustomXMLParts.Add XML:= _
        "<RCDP xmlns=""https://www.w3schools.com/furniture"">" & _
        "<arcprop id=""HeadingVisibilityA"">" & _
        "<visibility>True</visibility>" & _
        "<enabled>True</enabled>" & _
        "</arcprop>" & _
        "<arcprop id= ""HeadingVisibilityR"">" & _
        "<visibility>False</visibility>" & _
        "<checked>True></checked>" & _
        "</arcprop>" & _
        "</RCDP>"
  MsgBox ActiveDocument.CustomXMLParts(4).NamespaceURI
  MsgBox ActiveDocument.CustomXMLParts(5).NamespaceURI
  MsgBox ActiveDocument.CustomXMLParts(4).NamespaceManager.Item(1).NamespaceURI
  MsgBox ActiveDocument.CustomXMLParts(5).NamespaceManager.Item(1).NamespaceURI
End Sub