Slice tool (?)

I’m starting to work my way through Steve Wright’s Digital Compositing 2nd edition and was wondering if there’s a “slice tool” in the works for Blender’s compositor… “it’s ideal for checking edge values when pulling mattes from blue- and greenscreen material. You can also use it for examining color subsampling issues, edge sharpness, and other levels changes that are difficult to visualize with any other tool.”

I’m also looking for the Math node in the latest CVS but can’t seem to find it :wink: