arr.len = 5
arr[1..4] = [1, 4, 1]
sub.len = 3
arr[..3] = [3, 1, 4]
arr[2..] = [4, 1, 5]
sl[1..4] = [20, 30, 40]
mid[1..] = [30, 40]
msg[6..11] = world
msg[..5] = hello