Mix
Blends two images together based on a mask. If the mask is 0 you get the first input, if it is 1 you get the second.
user
Container for user-defined plugs. Nodes should never make their own plugs here, so users are free to do as they wish.
out
The output image generated by this node.
enabled
Turns the node on and off.
in
The input images
mask
The image which contains the mask channel.
mix
Control the blend between the two input images. 0 to take first input, 1 to take second input. Multiplied together with the mask.
maskChannel
The channel which controls the blend. Clamped between 0 and 1. 0 to take first input, 1 to take second input.