Hi folks, Thanks for all the replies!! This is great. I'm used to forums that take ages or never get back to you.. Abigail, ye've nailed it. That's exactly what I'm looking for, where "not throw" is part of the expression. I'm not familiar with the look ahead stuff but I've a couple of places with examples and I'll look at them. Incidentally are there any online resources you guys could recommend? Thanks again everyone, Mark.