SIMBAD references

We review the observed properties of extremely hot, hydrogen-deficient post-asymptotic giant branch (AGB) stars of spectral type [WC] and PG1159. Their H deficiency is probably caused by a (very) late helium-shell flash or an AGB final thermal pulse, laying bare interior stellar regions that are usually kept hidden below the hydrogen envelope. Thus, the photospheric elemental abundances of these stars allow us to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We summarize the state of the art of stellar evolution models that simulate AGB evolution and the occurrence of a late He-shell flash. We compare predicted elemental abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. Good qualitative and quantitative agreement is found. Future work can contribute to an even more complete picture of the nuclear processes in AGB stars.