Did you know that Spry came with a little XML tester? You can find it in the install zip here: /samples/data_region/DataSetExplorer.html. You can find an online version here. This is pretty handy - but you need to have the XML handy before testing.
Or so you did. Today I whipped up a quick application that lets you paste in XML and play with the xpath to see what kind of results you get:
Enjoy. It uses some of the Adobe code from the DataSetExplorer sample, so I can't take full credit.