Doppler velocity measurements at the location of the collisional PIL for AR 11158 (panels (a)–(d)) and AR 12017 (panels (e)–(h)). Different polarities (positive/white, negative/black magnetic field contours) are annotated, including those produced by different flux emergence episodes. To improve visual clarity and minimize masking from the magnetic field contours, the collisional PIL masks are either augmented in thickness, to show larger areas of the velocity patterns within them, or shown in an inset panel (panel (h)).