Restrictions can be applied at various levels: a government can apply them nationwide, an ISP can apply them to its clients, an employer to its personnel, a school to its teachers and/or students, a library to its patrons and/or staff, a parent to a child's computer or computer account or an individual to his or her own computer.
Restrictions can be applied at multiple levels: governments can regulate across the entire country, ISPs can control over their clients, employers can manage over their employees, schools can govern over instructors and students, libraries can monitor over users and staff, parents can supervise over their children's computers or accounts, and individuals can limit access to their own computers.