  Is the plasmon description within the non-local correlation of the van der
Waals density functional by Dion and coworkers (vdW-DF1) robust enough to
describe all exchange-correlation components? To address this question, we
design an exchange functional, termed LV-PW86r based on this plasmon
description as well as recent analysis on exchange in the large $s$-regime. In
the regime with reduced gradients $s=|\nabla n|/2n k_{\rm F}(n)$ smaller than
$\approx 2.5$, dominating the non-local correlation part of the binding energy,
the enhancement factor $F_x(s)$ closely resembles the Langreth-Vosko screened
exchange. In the $s$-regime beyond, dominated by exchange, $F_x(s)$ passes
smoothly over to the revised Perdew-Wang-86 form. Our tests indicate that
vdW-DF1(LV-PW86r) produces accurate separations and binding energies of the S22
data set of molecular dimers as well as accurate lattice constants of layered
materials and tightly-bound solids. These results suggest that vdW-DF1 has a
good plasmon description in the low-to-moderate $s$-regime.
