Treebeard is an XSLT IDE that allows one to load an XML file and an XSLT file (from the web or from the local file system), edit either file, and then perform transformations. Features include: Syntax highlighting,- Plug-able XSLT transformer,- FOP preview,- ability to save as PDF,- Template Browser,- Regular expression find,- and much more. Often XSLT is used in a background process. For example, transforming an XML document into an HTML page. The process used to write an XSLT document, at least for me, was to write the XSLT in a text editor, save it to a server, and then run the page to see if it transformed correctly. This is a very tedious process if one is just learning XSLT. Most commercial XSLT editor / IDEs are rather expensive, especially if you are an individual just trying to learn XML / XSLT. | 
