Tony Addyman managed to add debugging support for Xalan 2.4D1 in XSLT-process for Emacs! Now XSLT-process supports both Saxon and Xalan as XSLT debuggers.
Xalan debugging support in XSLT-process has been problematic because of the lack of source location information. During late June 2001, I've modified Xalan to add support for file and line information in both the source XML and in the stylesheet.
For some reasons this code was not working in the 2.2 release, which made the XSLT-process support unusable. Because of the rapid changes in Xalan and the lack of time, I've decided to drop the debugging support for Xalan in XSLT-process. Tony took up the support for this and he's doing a great job at it!