How does Link's shield work?

As the title says. Does it have a hitbox of its own and some attacks can sneak past Link, or is it like Zelda 1 where one side of him is completely shielded at one time, and the shield sprite doesn't actually matter? I do know that you can "use" your shield in front while you swim, and that it changes positions and guards your side as you'd expect when you are holding your sword out. By this I mean is it like the sword where it is a separate hitbox from Link.