I’ve made several updates. In particular, added over and under composite modes, along with several other things.
It probably operates more like people expect, now.
I plan on merging a lot of the functionality into the canvas target and layer widgets, to reduce the number of contraptions. Card target and layer contraptions will mostly remain the same. While the cards seem relatively limited compared to the canvases, they both serve a purpose: 1. being able to composite with the existing Decker drawing tools, and 2. a composited background for a canvas layer to trace over or underpaint.