Brushing modes:  Persistent, Transient, Undo

These are three different brushing modes.

Persistent:  When you brush a point, it retains its new color or glyph
when the brush is no longer over that point.

Transient:  As the brush moves off a point, it returns to the color and
glyph it had before the brush covered it.

Undo:  When Undo is activated, moving the brush over a point that was
painted during the preceding Persistent brushing action restores that
point to the state it had just before it was brushed.