The TRV is a document issued by a Canadian Immigration Visa Office outside Canada, showing that the holder has satisfied the requirements for admission to Canada as a visitor. TRVs may be for single entry or multiple entries. As a general rule, tourists are admitted for a period of six months. Temporary foreign workers and international students are admitted for varying periods of time, as determined on a case-by-case basis. Extensions may be applied for from within Canada. It is important to note that possession of a valid TRV does not necessarily mean that the Officer at the Canadian Port of Entry will admit the visitor into Canada. At the Port of Entry, all visitors must demonstrate that the purpose of their visit to Canada is of a temporary nature. Officers at the Port of Entry will deny admission to all persons who, in their opinion, do not intend to leave Canada at the expiry of their visitor status.