  We investigate the class of compact spaces which are embeddable into a power
of the real line $R^\kappa$ in such a way that c_0(\kappa) is dense in the
image. We show that this is a proper subclass of the class of Valdivia, even
when restricted to Corson compacta. We prove a preservation result concerning
inverse sequences with semi-open retractions. As a corollary we obtain that
retracts of Cantor or Tikhonov cubes belong to the above class.
