def cares_about(self, delta):
        """Return True if this observer "cares about" (i.e. wants to be
        called) for a this delta.

        """
        if (self.entity_id and delta.get_id() and
                not re.match(self.entity_id, str(delta.get_id()))):
            return False

        if self.entity_type and self.entity_type != delta.entity:
            return False

        if self.action and self.action != delta.type:
            return False

        if self.predicate and not self.predicate(delta):
            return False

        return True