I'm seeing a variety of requests for the ability to turn stamps into clipping masks, draw clipping mask, use text as clipping mask, etc.

So here's my proposal: just make a "clip" blend mode. It applies to anything that can have a blend mode. The effect is that any pixel that's not transparent becomes a clip pixel.

Also, there should be three of these things; one clips to FG, the other clips to BG, the third clips to anything that's below the selected object's layer.