[FFmpeg-user] Best place for despill filter?

[Michael Koch]

When I overlay a bluescreen foreground video over a background video, 
which is the best place for the despill filter? (a) before colorkey or 
(b) after colorkey or (c) after overlay?

[foreground](a),colorkey,(b)[fg];[background][fg]overlay,(c)

I found here an example for (c) but I doubt that this makes sense:
https://gist.github.com/kerbeh/fbe0cd0d89c424708c119e0a0d00ca88

Michael