  A series of semi-inclusive deep-inelastic scattering measurements on
deuterium, helium, neon, krypton, and xenon targets has been performed in order
to study hadronization. The data were collected with the HERMES detector at the
DESY laboratory using a 27.6 GeV positron or electron beam. Hadron
multiplicities on nucleus A relative to those on the deuteron, R_A^h, are
presented for various hadrons (\pi^+, \pi^-, \pi^0, K^+, K^-, p, and \bar{p})
as a function of the virtual-photon energy \nu, the fraction z of this energy
transferred to the hadron, the photon virtuality Q^2, and the hadron transverse
momentum squared p_t^2. The data reveal a systematic decrease of R_A^h with the
mass number A for each hadron type h. Furthermore, R_A^h increases (decreases)
with increasing values of \nu (z), increases slightly with increasing Q^2, and
is almost independent of p_t^2, except at large values of p_t^2. For pions
two-dimensional distributions also are presented. These indicate that the
dependences of R_A^{\pi} on \nu and z can largely be described as a dependence
on a single variable L_c, which is a combination of \nu and z. The dependence
on L_c suggests in which kinematic conditions partonic and hadronic mechanisms
may be dominant. The behaviour of R_A^{\pi} at large p_t^2 constitutes
tentative evidence for a partonic energy-loss mechanism. The A-dependence of
R_A^h is investigated as a function of \nu, z, and of L_c. It approximately
follows an A^{\alpha} form with \alpha \approx 0.5 - 0.6.
