Hong Kong (also known as Hongkong, which was common in older texts) has one of the world's most liberal economies and is a major international centre of finance and trade. A former British colony now administered by the PRC under the "one country, two systems" policy, Hong Kong is constitutionally entitled to a relatively high degree of autonomy; for example, it retains its own legal system, currency, customs, treaty negotiating rights, such as air traffic and aircraft landing rights, and immigration laws. Hong Kong even maintains its own road rules, with traffic continuing to drive on the left. Only national defence and diplomatic relations are responsibilities of the central government in Beijing.