Ah, thanks. I actually wasn't aware mobility was restricted like that. It's a little mind-boggling that China inadvertently emulated the national immigration problems of other countries with internal immigration[1], but at least it appears they are trying to fix it[2].

1: https://en.wikipedia.org/wiki/Hukou_system#Effect_on_rural_w...

2: https://en.wikipedia.org/wiki/Migration_in_China#Hukou_refor...