This is a bit more complexed than a normal user knows. Perhaps a few ex. in the help text? We do not have any at all
Actually yes you do 🙂
The subject is too large for a few random examples to be of any help. There are millions of possible examples, and still you one YOU want will be missing, so instead the Batch Update page includes a link to the official PHP regular expression documentation (the third link in my earlier post).