  We propose a generalized gradient approximation (GGA) for the angle- and
system-averaged exchange-correlation hole of a many-electron system. This hole,
which satisfies known exact constraints, recovers the PBEsol
(Perdew-Burke-Ernzerhof for solids) exchange-correlation energy functional, a
GGA that accurately describes the equilibrium properties of densely packed
solids and their surfaces. We find that our PBEsol exchange-correlation hole
describes the wavevector analysis of the jellium exchange-correlation surface
energy in agreement with a sophisticated time-dependent density-functional
calculation (whose three-dimensional wavevector analysis we report here).
