  We give an explicit description of the closure containment order (or "Bruhat
order") on the set of orbits of GL_p \times GL_q on the flag variety
GL_{p+q}/B, relative to the parametrization of the orbits by combinatorial
objects called "clans". This leads to a corresponding description of the
closures of such orbits as sets of flags satisfying certain incidence
conditions encoded by the parametrizing clans.
