  The fully covariant formulation of transformation optics is used to find the
configuration of a cloaking device operating in an expanding universe modelled
by a Friedmann-Lema\^itre-Robertson-Walker spacetime. This spacetime cloak is
used as a platform for probing the covariant formulation of transformation
optics, thereby rigorously enhancing the conceptual understanding of the
theory. By studying the problem in both comoving and physical coordinates we
explicitly demonstrate the preservation of general covariance of
electrodynamics under the transformation optics procedure. This platform also
enables a detailed study of the various transformations that arise in
transformation optics. We define a corporeal transformation as the
"transformation" of transformation optics, and distinguish it from coordinate
and frame transformations. We find that corporeal transformations considered in
the literature have generally been restricted to a subset of all possible
corporeal transformations, providing a potential mechanism for increased
functionality of transformation optics.
