Excellent question. The behaviors of a couple of laptops I used is that if you hold down the touchpad button and your finger reaches the edge of the touchpad, then the computer will give you a small pre-defined constant velocity in that direction (e.g. if your finger is at the right edge then there will be a cursor velocity to the right) until either your finger is no longer on an edge of the touchpad or you lift the touchpad button. It's a reasonable solution but feels hacky compared to TrackPoint (infinite range) or trackball (infinite range) or mouse (can lift the mouse (not the button) and do more strokes).