Online PHP editor | vld for OWSq6

<?php const A = [1 => ['undefined' => ['index' => 20 ], [40, 45, 48]], 'undefined' => ['index' => 60]]; const D_1 = A[1]{'undefined'}['index'] ? A[1]{'undefined'}['index'] : 1; const D_2 = A['undefined']{'index'} ? A['undefined']{'index'} : 2; const D_3 = A[1]{0}{2} ? A[1]{0}{2} : 3; // Error x 2. const D_4 = A[1]{0} ? A[1]{0} : 4; echo D_1, D_2, D_3, D_4;