Generalized Chiral Perturbation Theory
  The Generalized Chiral Perturbation Theory enlarges the framework of the standard $\chi$PT, relaxing certain assumptions which do not necessarily follow from QCD or from experiment, and which are crucial for the usual formulation of the low energy expansion. In this way, experimental tests of the foundations of the standard $\chi$PT become possible. Emphasis is put on physical aspects rather than on formal developements of G$\chi$PT. 
M. Knecht, J. Stern