Check if either the datastream content or profile fields have changed
        and should be saved to Fedora.

        :rtype: boolean

def isModified(self):
        """Check if either the datastream content or profile fields have changed
        and should be saved to Fedora.

        :rtype: boolean
        """
        # NOTE: only check content digest if locally cached content is set
        # (content already pulled or new content set); otherwise this
        # results in pulling content down to checksum it !
        return self.info_modified or \
            self._content and self._content_digest() != self.digest