This field only appears if you configured the change stream with
fullDocument set to updateLookup. When you configure the change stream
with updateLookup, the field represents the current
majority-committed version of the document modified by the update operation.
The document may differ from the changes described in
:ref:`updateDescription <|idref|-updateDescription>` if any other
majority-committed operations have modified the document between the original
update operation and the full document lookup.
For more information, see :ref:`Lookup Full Document for Update Operations <change-streams-updateLookup>`.