Theoretical implications of IXPE polarimetric measurements for blazars

I will review the theoretical implications of the IXPE and multifrequency polarimetric measurements of the emission from blazars. In particular, for highly-synchrotron peaked BL Lacs current measurements show a strong frequency-dependency of the degree of polarization, commonly attributed to a stratified emission region, possibly associated to shock acceleration. I will discuss this interpretation, together with possible alternatives.