The Bangsamoro Basic Law (BBL) is a law that seeks to abolish the Autonomous Region of Muslim Mindanao and establishes the Bangsamoro political identity on its place. It was based on the Comprehensive Agreement of the Bangsamoro signed by the Philippine Government together with the the MILF (Moro Islamic Liberation Front) on March 2014.
Well, you can say the BBL is law the allows the Bangsamoro to rule ARMM. Its a law that allows a nation-like sovereignty to exist within a nation, in this case the Bangsamoro under the Philippines.