Regex Expression

Regex function are a plugin you would need to deploy first. Admin console -> Plugins

I highly recommend that you look through the documentation, particularly the set of Text Functions which can be found here:  docs.appian.com/.../Appian_Functions.html

One of my biggest pet peeves going back to the original Appian Forums is how frequently everyone jumps at the chance to suggest "REGEX!" despite the fact that there's almost always a far more simple and lightweight (and possibly faster) out of the box Appian function that does the exact same thing without having to download and then learn the regex plugin.  The chances that you can do it without even needing regex are pretty high.