  Time-resolved SALT spectra of the short-period, dipping X-ray transient,
Swift J1357.2-0933, during its 2017 outburst has revealed broad Balmer and
HeII4686 absorption features, blue-shifted by ~600 km/s. Remarkably these
features are also variable on the ~500s dipping period, indicating their likely
association with structure in the inner accretion disc. We interpret this as
arising in a dense, hot (>~30,000K) outflowing wind seen at very high
inclination, and draw comparisons with other accretion disc corona sources. We
argue against previous distance estimates of 1.5 kpc and favour a value >~6
kpc, implying an X-ray luminosity L_X>~4x10^{36} erg/s$. Hence it is not a very
faint X-ray transient. Our preliminary 1D Monte-Carlo radiative transfer and
photoionization calculations support this interpretation, as they imply a high
intrinsic L_X, a column density N_H>~10^{24} cm^{-2} and a low covering factor
for the wind. Our study shows that Swift J1357.2-0933 is truly remarkable
amongst the cohort of luminous, galactic X-ray binaries, showing the first
example of He II absorption, the first (and only) variable dip period and is
possibly the first black hole 'accretion disc corona' candidate.
