  The generalised vector meson dominance model (GVDM) gives a good description
of F_2 data at very low Q^2. At intermediate Q^2 a GVDM component avoids
problems when applying the large-Q^2 DIS formalism, such as a negative gluon
distribution in the proton. The fluctuations of the exchanged photon into
vector mesons is also a natural part of a model with hadronic fluctuations of
the target proton, which gives a good description of the non-perturbative
x-shape of the proton's parton density functions at the starting scale Q^2_0
for DGLAP evolution.
