Asymptotic expansions of generalized Nevanlinna functions
are investigated by means of a factorization model involving a part of the generalized zeros and poles of nonpositive type of the function
. The main results in this paper arise from the explicit construction of maximal Jordan chains in the root subspace R
) of the so-called generalized Friedrichs extension. A classification of maximal Jordan chains is introduced and studied in analytical terms by establishing the connections to the appropriate asymptotic expansions. This approach results in various new analytic characterizations of the spectral properties of selfadjoint relations in Pontryagin spaces and, conversely, translates analytic and asymptotic properties of generalized Nevanlinna functions into the spectral theoretical properties of self-adjoint relations in Pontryagin spaces.