Translations:Draft tutorial Outdated/23/en

A note about upgrade & downgrade
Now, you must be aware that the openCasCade kernel that FreeCAD is built upon, is a 3D kernel. It is made primarily for 3D operations. When it has to cut or unite planar faces, like we are doing now with upgrade/downgrade operations, it sometimes does strange things, and subsequent operations (like other upgrades/downgrades) sometimes don't give the expected results. Of course with time those behaviours will end up being corrected by the FreeCAD developers, but it is wise to know alternative ways to solve immediate problems.