<P> Sometimes border controls exist on internal borders within a sovereign state . For example, in the People's Republic of China, there are border controls at the borders among the mainland and the special administrative regions of Hong Kong and Macau . All persons need to present their passports or other types of travel documents to cross the border . For example, Hong Kong Permanent Identity Card and Home Return Permit are required for Hong Kong Permanent Residents who are Chinese citizens to cross the border . Another example is the Malaysian states of Sabah and Sarawak, each having separate border controls from the rest of Malaysia . Also Norway exercise passport check when travelling between mainland Norway and the archipelago of Svalbard which is non-Schengen area . Travelling between Guam and the rest of the United States is also such an example, since Guam is not defined to be part of the United States immigration zone . </P> <P> In some cases countries can introduce controls that functions as border controls but aren't border controls legally and don't need to be performed by government agencies . Normally they are performed and organised by private companies, based on a law that they have to check that passengers don't travel into a specific country if they aren't allowed to . Such controls can take effect in one country based on the law of another country . Even if they aren't border controls they function as such . The most prominent example is airlines which check passports and visa before passengers are allowed to board the aircraft . Also for some passenger boats such check are performed before boarding . </P>

Where is the boarding area in animal crossing