


How closely it's allowed to approach the line is determined by the Area Scaling setting. I dragged the fill-in mono pen tool from left to right against this exaggerated pencil line, and the mono pen cannot color underneath the line, only up against its left side. When brushing up against a textured line, the coloring tool will fill in the small details along the edge of the line, however it will not be able to fill in deeper inside the line if the line is partially transparent. The edges of your brush may exceed the line without coloring, but keep in mind the center point. The "be gentle" is referencing this if the center point of your brush passes over a line to the other side, it will allow color again. This makes it great for working with big brush sizes in small details, since the center point is all that matters. If you drag the center of your brush across an area you want to color and the center point meets a line from the reference layer, color will not exceed that line unless the center point of your brush passes over the line. lines) in the reference layer, it will not allow color. If the center point of your brush is above pixels that have a nonzero opacity (i.e. If the center point of your brush is above pixels that are transparent in the reference layer, it will allow color. The setting appears to look at the position of the center point of your brush, and compares that to the reference layer. I just played around with this for a few minutes, it looks very useful.
