  Radiative energy loss of a highly virtual quark originating from a
deep-inelastic electron scattering plays a crucial role in production of
leading hadrons off nuclei. The density of energy loss for gluon radiation
turns out to be time- and energy--dependent in inclusive hadron production.
Important phenomena involved are Sudakov's suppression of no radiation of that
part of gluon spectrum, which is forbidden by energy conservation, and color
transparency, which suppresses the final state interaction of the produced
colorless wave packet. We model the soft part of hadronization, which usually
is supposed to be due to the color strings, using also the gluon radiation and
nicely reproduce the string parameters. Our parameter-free calculations provide
a good agreement with available data on $z_h$-dependence of the quark
fragmentation function in vacuum, as well as $\nu$-, $z_h$- and
$Q^2$-dependence of nuclear effects. We come to the conclusion that the energy
range of ELFE - HERMES is most sensitive to the underlying dynamics of
hadronization provided that nuclear targets are used.
