  Precise measurements of charged-kaon multiplicities in deep inelastic
scattering were performed. The results are presented in three-dimensional bins
of the Bjorken scaling variable x, the relative virtual-photon energy y, and
the fraction z of the virtual-photon energy carried by the produced hadron. The
data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off
an isoscalar 6 LiD target. They cover the kinematic domain 1 (GeV/c)2 < Q2 < 60
(GeV/c)^2 in the photon virtuality, 0.004 < x < 0.4, 0.1 < y < 0.7, 0.20 < z <
0.85, and W > 5 GeV/c^2 in the invariant mass of the hadronic system. The
results from the sum of the z-integrated K+ and K- multiplicities at high x
point to a value of the non-strange quark fragmentation function larger than
obtained by the earlier DSS fit.
