I wish ON1 PR was more consistent with its terminology about masking. For a mask pertaining to an entire layer the ‘white reveals and black conceals’ rhyme makes sense. However, for adjustments reveal makes more sense to me to mean that the original image is seen rather than the adjustment. ‘Paint’ really means: paint with white onto the mask to include areas for which you want to apply the adjustment. Erase means paint with black onto the mask for areas to which you want to omit/remove the adjustment.

In the Quick Mask Brush, which is the newer name for what was the older AI Quick Mask, the information box (which still bears the title of AI Quick Mask) mentions ‘red Drop mode’ for areas you want to paint-out, and ‘green Keep’ mode for areas you want to paint-in. The control menu bar has ‘Keep / Erase’.

The Line Mask tool is even more confusing. It has controls for Paint / Erase. For a Local adjustment which begins with an all black mask, Paint mode does nothing. It should, but does not, fill the area enclosed by lines with white. If you invert the mask to all white, draw an area bounded by lines, then Erase does result in black painted within the bounded area.