  Recent results in the theory of multiphoton spectra for coherent radiation
sources are overviewed, with the emphasis on channeling radiation. For the
latter case, the importance of the order of resummation and averaging is
illustrated. Limiting shapes of multiphoton spectra at high intensity are
discussed for different channeling regimes. In some spectral regions, there
emerges an approximate correspondence between the radiative energy loss and the
electron integrals of motion.
