The lower part of the VSL effect's property window contains the standard VSL editor. By checking the Advanced option, you get access to the editing tools. See the Materials chapter for VSL programming instructions.
The VSL objects of the image processing tree see all channels of the system and can freely perform any suitable computations using the channels. Because of the auto-configuration property of the post processing system, referring a channel from a VSL object automatically includes the channel in the post processing data flow.