  We have compared the optical emission line ratios of type 2 quasars from
Zakamska et al. with standard AGN photoionization model predictions, Seyfert
2s, HII galaxies, and narrow line FRII radio galaxies. Moderate to high
ionization narrow line radio galaxies and Seyfert 2s are indistinguishable from
type 2 quasars based on their optical line ratios.
  The standard AGN photoionization models, widely discussed for other type 2
AGNs, can reproduce successfully the loci and trends of type 2 quasars in some
of the main diagnostic diagrams. These models are not exempt of problems and
the discrepancies with the data are the same encountered for other type 2 AGNs.
As for these, realistic models must take into account a range of cloud
properties, as widely demonstrated in the literature.
  We also study the possible impact of stellar photoionization.
