Recently I've been doing some software consultancy work on a payments system, to do with SEPA integration, and ISO 20022.
As part of that I've come across Steve Muench's Muenchian Method of Grouping in XSLT. It's been around for 13 years, but this is the first time I've needed it. I won't describe it here - I couldn't improve on Jenni Tennison's description here - I just want to state well done Steve. Given the constraints of XSLT 1.0 it is a very neat, elegant and efficient way to solve that particular issue.
Thanks very much Steve!