It depends on what you know about the input. If you know it says "At Expiry" then you don't need to look at the input at all, just write "Expiry" to the output. If you want everything from the fourth character, use substring(). If you want everything after the first space, use substring-after().
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference