Rated 5 out of 5 stars
you can learn a lot about regexp starting from here.
use the try it editor for quick preview of what exactly happens. its really not as hard as you may think.
note: i haven't used the addon, i'm just offering help on regexp for all the people that miss this addon. i like the said features of this addon. the idea of previewing redirection urls and using it preview any short url redirection is really great.