I've noticed that proper clipping functions have been requested for years now. Please take a serious look at adding this functionality. One of the first thing I'm always asked about Plant 3D, is "where's the clipping function, the sectioning tool doesn't work as expected?". Plant 3D has come a long way, but until a proper clipping function is added, I will always shy away from its use. This should be a top priority for Autodesk.