I don't understand what they are doing? I don't recall @ having special significance in a URL? I can only guess that they have two separate steps for transform

I don't understand what they are doing? I don't recall @ having special significance in a URL? I can only guess that they have two separate steps for transforming URLs into links and transforming @replies into links. Then they first run the URL transformer and then the @replies transformer, which would of course mess up the URL. I have solved that problem in one of my Twitter apps (transforming both in one go), maybe I should send them a code snippet...