From left to right: examples of observed (black) and inverted (red) Stokes-I, -Q, -U, and -V profiles at the 20 positions on the sub-FOV labelled (a) in Fig. A.1, taken during the pore formation at 13:58 UT. Spectra are normalized to the continuum intensity. Numbers on the bottom left in each sub-panel of the Stokes-I figure indicate the position of the analysed pixel expressed in arcsec with respect to the sub-FOV shown in Fig. A.1. Values of the stray-light fraction, LOS magnetic field strength (kG), field inclination and azimuth (degree), and LOS velocity (km s^-1) derived from our data analysis (at optical depth logτ₅₀₀ = 1) at the same positions of the shown profiles are listed in Table A.1; the values are cut at 2 decimal digits.