金剛經纂要刊定記 3.36

3.36

正念者，如理而念名為正念。念即念慧，謂離沈掉有無等。不動謂不動於正念也。

As for "mindfulness," being mindful in accordance with principle is called mindfulness. Mindfulness is the wisdom of mindfulness, meaning freedom from sinking, agitation, being, nonbeing, and so forth. "Unmoving" means being unmoving in mindfulness.