Do you have a citation for that? I have always understood the rules to be that you should always remember the car in front of you can make an emergency stop at

Do you have a citation for that? I have always understood the rules to be that you should always remember the car in front of you can make an emergency stop at any time for any reason, and it is always your fault if you hit them (unless they just moved into your lane). Conversely if you need to stop suddenly, e.g. something has crossed the road in front of you (or you think it has), you don't worry about the vehicles behind, you just stop.