Odd question, but it's been something bugging me for a while.
Can anyone recommend any good (and preferably free) XSL/XSLT/X-Path editor/syntax checker/validator? I was trying to convert an existing project into using PHP-generated XML with XSL templates to do the actual page rendering, and debugging just using a browser was almost impossible - every single browser had the most cryptic error messages I've ever seen for XML/XSL issues.
I've seen several commercial editors and plugins for Eclipse, but nearly nothing on the open source and/or free software side of the fence...and to add insult to injury quite a few of the commercial ones didn't even have a demo to examine.