A geographical region where the same time-zone rules apply. !(p) Time-zone information is categorized as a set of rules defining when and how the offset from UTC/Greenwich changes. These rules are accessed using identifiers based on geographical regions, such as countries or states. The most common region classification is the Time Zone Database (TZDB), which defines regions such as 'Europe/Paris' and 'Asia/Tokyo'. !(p) The region identifier, modeled by this class, is distinct from the underlying rules, modeled by {@link ZoneRules}. The rules are defined by governments and change frequently. By contrast, the region identifier is well-defined and long-lived. This separation also allows rules to be shared between regions if appropriate.