The ASEAN Charter is a constituent instrument of a regional intergovernmental organisation comprising how many Southeast Asian states?  
ASEAN Charter: The ASEAN Charter is a constituent instrument of the Association of Southeast Asian Nations (ASEAN). Association of Southeast Asian Nations: The Association of Southeast Asian Nations (ASEAN , ) is a regional intergovernmental organisation comprising ten Southeast Asian states which promotes Pan-Asianism and intergovernmental cooperation and facilitates economic, political, military, educational and cultural integration amongst its members and Asian states.
ten