Hi Christian,
""""""""""""If i understand
We could say that when we are creating an hole, this hole is just an hidden part .
and sometime peripheral contour can reveal the limit""""""""""
Sure! Here is a little doodling with trim boundries and untrimming and retrimming them. Note showing points reveals the underlying surface still there. The "trims" are just "hide this part and hide this part" of a NURBS surface.
