+The stretched distance is extended in one of two modes depending on
+[[xstep]]. If [[xstep == 0]], then the pulling is continuous, at
+least within the limits of the inherent discretization of a time
+stepped approach. At any rate, the timestep is limited by the maximum
+allowed timestep [[dt_max]] and the maximum allowed unfolding
+probability in a given step [[P]]. In the second mode [[xstep > 0]],
+and the end to end distance increases in discrete steps of that
+length. The time between steps is chosen to maintain an average
+unfolding velocity [[v]]. This approach is less work to simulate than
+smooth pulling and also closer to the reality of many experiments, but
+it is practically impossible to treat analytically. With both pulling
+styles implemented, the effects of the discretization can be easily
+calculated, bridging the gap between theory and experiment.
+