held instead that the habeas court erred by not following the CCA 's 2004 decision in Ex parte Briseno , 135 S. W. 3d 1 , which adopted the definition of , and standards for assessing , intellectual disability contained in the 1992 -LRB- ninth -RRB- edition of the American Association on Mental Retardation manual -LRB- AAMR-9 -RRB- , predecessor to the current AAIDD-11 manual