Hi Pilou, there's an image in Jamie's previous post here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4068.4

The "UntrimAll" plugin will do a combination of Edit > Separate to break a solid into individual separate surfaces, and then also remove all trim curves from those surfaces so that you'll see the full underlying surfaces (this is the same as selecting all edges of those surfaces and pushing delete).

So if you have a solid like the object on the right-hand side of Jamie's post above, when you run UntrimAll you will get a result with all surfaces untrimmed like the result on the left-hand side of Jamie's image.

- Michael