如何使用nom精确匹配一个字节？

use nom::bytes::complete::tag;
use nom::IResult;

fn main() {
    let input = b"Hello, World!";
    let result: IResult<_, _> = tag(b"H")(input);

    match result {
        Ok((remaining, matched)) => {
            println!("Matched: {:?}", matched);
            println!("Remaining: {:?}", remaining);
        }
        Err(err) => {
            println!("Error: {:?}", err);
        }
    }
}