MB4 232a: Accepting the Eruv Chatzeros on Behalf of Others (366:9-10 - part 1)

One person can make an eruv chatzeros on behalf of the other residents but someone else has to accept it on their behalf (זכין לאדם שלא בפניו). The one who accepts it has to have in mind the other residents plus any future residents (otherwise מעיקר הדין a new eruv would need to be made).

Who can accept the eruv on behalf of the residents?

What if the population of the enclosed area increases?