If you’ve ever been working inside an Edit-Poly modifier and needed to move vertices along a non-ortho edge, you’ve realized it can be difficult. If you scroll down in the Command Panel and find the “Edit Geometry” rollout, inside you’ll see a set of parameters named “Constrain” with the options “None”, “Edge”, “Face” and “Normal”. Click “Edge” and now your vertex selection will ONLY move along the shared edges of the vertex selection! Also works with Face and Normal mode as well as with other Sub-object levels selected (edge, border, polygon, element).