+In the Overlay plugin's parameter window you can choose the overlay order
+to select which track plays the role of the "bottom layer" and which plays the
+role of the "top layer". For some overlay modes this can make quite a
+difference, for example the top layer is subtracted from the bottom layer for
+"Subtract" mode. Also in the parameter window, you can choose on which of the tracks
+to overlay the combined output. (Hint: in most cases, you will want to mute
+the other track so you only see the combined output).
+