  We first provide a review of the properties of warm absorbers concentrating
on what we have learned from ROSAT and ASCA. This includes dusty and dust-free
warm absorbers, non-X-ray emission and absorption features of warm absorbers,
and the possible warm absorber interpretation of the peculiar 1.1 keV features.
  We then discuss facets of warm absorbers by a more detailed investigation of
individual objects: In a first part, we discuss several candidates for dusty
warm absorbers. In a second part, we review and extend our earlier study of a
possible relation between warm absorber and CLR in NGC 4051, and confirm that
both components are of different origin (the observed coronal lines are
underpredicted by the models, the warm absorber is too highly ionized). We then
suggest that a potential overprediction of these lines in more lowly ionized
absorbers can be avoided if these warm absorbers are dusty. In a third part, we
present first results of an analysis of a deep ROSAT PSPC observation of the
quasar MR2251-178, the first one discovered to host a warm absorber. Finally,
we summarize our scrutiny under which conditions a warm absorber could account
for the dramatic spectral variability of the Narrow-line Seyfert 1 galaxy
RXJ0134-4258.
