I think what's causing the hang is using the site. I gave it [a-f0-9]{8}(?:-[a-f0-9]{4}){3}-[a-f0-9]{12} and it sat thinking about things for a few minutes. So

I think what's causing the hang is using the site. I gave it [a-f0-9]{8}(?:-[a-f0-9]{4}){3}-[a-f0-9]{12} and it sat thinking about things for a few minutes. So I tried the reverse and asked it "Match a UUID" and it sat and thought about things. Now I am enlightened.