  The single-differential and fully integrated cross sections for quasifree
$\pi^{+}\pi^{-}$ electroproduction off protons bound in deuterium have been
extracted for the first time. The experimental data were collected at Jefferson
Laboratory with the CLAS detector. The measurements were performed in the
kinematic region of the invariant mass $W$ from 1.3 to 1.825 GeV and the photon
virtuality $Q^{2}$ from 0.4 to 1.0 GeV$^2$. Sufficient experimental statistics
allowed for narrow binning in all kinematic variables, while maintaining a
small statistical uncertainty. The extracted cross sections were compared with
the corresponding cross sections off free protons, which allowed us to obtain
an estimate of the contribution from events in which interactions between the
final-state hadrons and the spectator neutron took place.
