Method boundary

std/re/src/main/matcher.rs:250–254

(&self, pos: usize)

    }

    fn boundary(&self, pos: usize) -> bool {
        let before = pos > 0 && is_word(self.input[pos - 1]);
        let after = pos < self.input.len() && is_word(self.input[pos]);
        before != after
    }
}

fn empty_caps(ngroups: usize) -> Caps {