With light, heat, or R-O-O-R, the organic starting material will undergo homolytic cleavage around the C-H sigma bonds and the Br-Br bonds, this will cause radicals to form. One of the Br radicals will go combine with the oxygen to form H-Br and the other Br radical will go to the C radical. This is regioselective in the sense that the most stable radical will form the major product, this also goes to the kinetics of the reaction. so the result will be CH3CHBrCH3 + H-BR.