The XSL elements give you the chance to work with more advanced XSL functions that are not covered by the WYSIWYG interface of XSLfast. Open an XSL element and double click it. A simple text editor opens where you can enter XSL and XSL-FO commands. Also there are XSLT functions at your disposal, they can be found at the right side of the editor window. Apart from the simple editor and the missing function to group this element to an XML node it has the same handling as text elements. Please find more information about XSL programming in the specific literature or the Internet, e.g. at http://www.w3.org/Style/XSL/.