evidence: Macau's status since reverting to PRC sovereignty in December 1999 is defined in the Sino-Portuguese Joint Declaration (1987) and the Basic Law, Macau's constitution promulgated by China's National People's Congress (NPC) in March 1993. The Joint Declaration and the Basic Law specify that Macau's social and economic system, lifestyle, rights, and freedoms are to remain unchanged for at least 50 years. Under the concept of "one country, two systems" articulated in these documents, Macau enjoys a high degree of autonomy except in defense and foreign affairs. Macau officials, rather than PRC officials, run Macau through the exercise of separate executive, legislative, and judicial powers. Macau maintains its own separate currency, customs territory, immigration and border controls, and police force.