What does this Zig snippet output?

1const std = @import("std");
2pub fn main() void {
3    const arr = [_]u8{ 10, 20, 30, 40, 50, 0 };
4    const sentinel: [:0]const u8 = arr[0..5 :0];
5    std.debug.print("{d}\n", .{sentinel.len});
6}