What does a flashing green pedestrian signal mean?

1. ①A pedestrian who has just arrived at the crosswalk may start crossing if he or she runs.
2. ②A pedestrian who is crossing must stop where he or she is and wait for the next green signal.
3. ③Pedestrians must not start crossing, and those already crossing must quickly finish or stop crossing and return to the sidewalk.
4. ④Once the green starts flashing, drivers may pass through the crosswalk even if pedestrians are still on it.