CHANGELOG 5.3 The first major release Support for the following C++23 library features mdspan (P0009R18, P2599R2, P2604R0, P2613R1, and P2763R1) extents, dextents (P0009R18) layout_left, layout_right, layout_stride (P0009R18) default_accessor (P0009R18) Support for the following C++26 library features submdspan (P2630R4, P3663R3, and P3982R2) dims (P2389R2) layout_left_padded, layout_right_padded (P2642R6) mdspan::at() (P3383R3) Support for the following proposed standardization features in the Experimental namespace: mdarray (P1684)