Web developers who share ideas will likely be aware of jsFiddle and SQL Fiddle, which are used to demo snippets of JavaScript and SQL respectively. I’d like to see an XML equivalent, in which an XML snippet can be provided, and an XPath query used to select the relevant data.

This would be partly an educational tool, to allow people to experiment with various XPath queries, and partly a way of sharing XPath queries over the web. Last I checked, there was nothing like this – but someone will surely fill the gap one day!