def http__refreshEtag():
    """        While it may make sense to use the ZODB Object Id or the
        database mtime to generate an Etag, this could
        fail on certain REQUESTS because:

         o The object is not stored in the ZODB, or

         o A Request such as PUT changes the oid or database mtime
           *AFTER* the Response has been written out, but the Etag needs
           to be updated and returned with the Response of the PUT request.

        Thus, Etags need to be refreshed manually when an object changes.
        """
