Malaysia is a federal constitutional elective monarchy, and the only federation in Southeast Asia. The system of government is closely modelled on that of the Westminster parliamentary system, a legacy of British colonial rule. The head of state is the Yang di-Pertuan Agong, commonly referred to as the King. The King is elected to a five-year term by and from among the nine hereditary rulers of the Malay states; the other four states, which have titular Governors, do not participate in the selection. By informal agreement the position is systematically rotated among the nine, and has been held by Abdul Halim of Kedah since December 2011 The King's role has been largely ceremonial since changes to the constitution in 1994, picking ministers and members of the upper house.