These expansions are certainly possible and I'm planning to investigate whether they have performance benefits. One interesting discovery we made last weeks is that `(a|b|c)` actually produces a larger state table than `[abc]`. This was both the case for Java and Vim. While the performance gains are minute, nevertheless, they are gains.

I haven't checked if "a{4}", for example, is faster than "aaaa" or produces fewer states. But it's something I am interested in. I just haven't had enough time this week.