I originally took a guess this might project selected curves onto a target surface using the active CPlane Top direction,
then deletes the original input curves after creating the projected result.

Project deleteinputs=true cplaneside=top usecplane

then edit: checked here = it's more like flatten something to the cplane...

https://moi3d.com/forum/lmessages.php?webtag=MOI&msg=10971.4