  Halo nuclei are located far from stability and exhibit a very peculiar
structure. Due to their very short lifetime, they are often studied through
reactions. Breakup reactions are of particular interest since their cross
sections are large for these loosely-bound nuclei. Inclusive measurements of
breakup--also called knockout reactions--have even higher statistics. In this
proceeding, we study which nuclear-structure information can be inferred from
the parallel-momentum distribution of the core of one-neutron halo nuclei after
the knockout of its halo neutron. In particular, we analyse the influence of
the ground-state wavefunction, the presence of excited states within the
halo-nucleus spectrum and resonances in the core-neutron continuum. Our
analysis shows that such observables are sensitive to the tail of the
ground-state wavefunction. The presence of excited state decreases the breakup
strength, and this flux is transferred to the inelastic-scattering channel.
This indicates a conservation of the flux within each partial wave. We also
show that the parallel-momentum distributions are insensitive to the existence
of resonances within the continuum, they can thus be ignored in practice. This
independence on the continuum argues that the parallel-momentum distributions
are ideal observables to extract very precisely the ANCs of halo nuclei.
