In the world of serialized data, there's only been a few key technologies and XML was certainly the forerunner. It's been around since the mid 90's and was originally added into FileMaker around version 5 - if memory serves. The implementation of XML/XSLT/XPATH wasn't fully complete with compatible functions and it only works as an import and export feature via the use of an XSLT style sheet.
So, these days, you have the choice of learning xpath and using a plug-in in order to extract data out of XML or you can just convert it into a format such as JSON for simply pulling the data out using FileMaker 16's new JSON functions. With this technique file, and video, you'll be well on your way to extracting data out of XML files if you need to do so.
Click the title or link to this article to view the video.