@array = ([ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ]);
          ^^^^^^^^^^^  ^^^^^^^^^^^  ^^^^^^^^^^^
            $i = 0        $i = 1       $i = 2

# @array          = <nested_array1>, <nested_array2>, <nested_array3>;
# <nested_array1> = 1, 2, 3
# <nested_array2> = 4, 5, 6
# <nested_array3> = 7, 8, 9