I recently discovered the joy of XPath, thanks to a talk at one of the IndyJUG meetings a couple of months ago. Once I got the most basic of grasps on XPath queries, I was able to start churning out some pretty slick scraped RSS feeds for things like Pollstar artist and city searches, eBay searches, Iconfactory and Konfabulator recent updates, and a bunch of others. Actually, that little project’s a good showcase of a couple of my favorite tools, Henplus and Tagsoup.
Anyway, one of the biggest difficulties I ran into was visualizing the results of XPath queries without having to dump the results with an XSL stylesheet, which was a less-than-elegant solution. After a bit of Googling, I came up with a tool called XPE.
It's the only "free" (for any definition of free) tool I’ve found so far that allows me to evalue XPath statements and see their affect on a document.
XPE isn't terribly fancy in the interface department, and can be a little sluggish at times, but it is extremely effective. The default view on startup is a graphical tree representation of the nodes in the loaded XML document. When you evaluate an XPath, XPE highlights the matched elements (but not text nodes) and expands the short-format to it's fully-qualified (and durn ugly, I might add) form.
All in all, a very nice Open Sourced tool (BSD license).