  The ionizing spectral energy distribution of quasars exhibits a steepening of
the distribution shortward of ~ 1200 A. The change of the power-law index from
approximately -1 (near-UV) to -2 (far-UV) has so far been interpreted as being
intrinsic to quasars. We consider the possibility that the steepening may
result from a tenuous absorption component that is anticorrelated with large
mass overdensities. UV sensitive satellites, whose detectors can extend down to
1000 A, can set a useful limit to such an absorption component through the
search of a flux increase in the window 1050-1190 A (observer frame) with
respect to an extrapolation of the continuum above 1230 A. Since the recent
FUSE or HST-STIS data do not show any obvious discontinuity in this region,
this effectively rules out the possibility that intergalactic HI absorption is
very important, and it is concluded that most if not all of the steepening is
intrinsic to quasars. A smaller flux discontinuity of order 1% cannot, however,
be ruled out yet and would still be consistent with the warm-hot intergalactic
component if it amounts to 30% of the baryonic mass, as predicted by some
models of large scale structure formation, provided its temperature lies around
10^{5.5} K.
